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MariaDB-open-code/sql/mdl.cc
Sergey Vojtovich 18985d8471 MDEV-19749 - MDL scalability regression after backup locks 
Statements that intend to modify data have to acquire protection
against ongoing backup. Prior to backup locks, protection against
FTWRL was acquired in form of 2 shared metadata locks of GLOBAL
(global read lock) and COMMIT namespaces. These two namespaces
were separate entities, they didn't share data structures and
locking primitives. And thus they were separate contention
points.

With backup locks, introduced by 7a9dfdd, these namespaces were
combined into a single BACKUP namespace. It became a single
contention point, which doubled load on BACKUP namespace data
structures and locking primitives compared to GLOBAL and COMMIT
namespaces. In other words system throughput has halved.

MDL fast lanes solve this problem by allowing multiple contention
points for single MDL_lock. Fast lane is scalable multi-instance
registry for leightweight locks. Internally it is just a list of
granted tickets, close counter and a mutex.

Number of fast lanes (or contention points) is defined by the
metadata_locks_instances system variable. Value of 1 disables fast
lanes and lock requests are served by conventional MDL_lock data
structures.

Since fast lanes allow arbitrary number of contention points, they
outperform pre-backup locks GLOBAL and COMMIT.

Fast lanes are enabled only for BACKUP namespace. Support for other
namespaces is to be implemented separately.

Lock types are divided in 2 categories: lightweight and heavyweight.

Lightweight lock types represent DML: MDL_BACKUP_DML,
MDL_BACKUP_TRANS_DML, MDL_BACKUP_SYS_DML, MDL_BACKUP_DDL,
MDL_BACKUP_ALTER_COPY, MDL_BACKUP_COMMIT. They are fully compatible
with each other. Normally served by corresponding fast lane, which is
determined by thread_id % metadata_locks_instances.

Heavyweight lock types represent ongoing backup: MDL_BACKUP_START,
MDL_BACKUP_FLUSH, MDL_BACKUP_WAIT_FLUSH, MDL_BACKUP_WAIT_DDL,
MDL_BACKUP_WAIT_COMMIT, MDL_BACKUP_FTWRL1, MDL_BACKUP_FTWRL2,
MDL_BACKUP_BLOCK_DDL. These locks are always served by conventional
MDL_lock data structures. Whenever such lock is requested, fast
lanes are closed and all tickets registered in fast lanes are
moved to conventional MDL_lock data structures. Until such locks
are released or aborted, lightweight lock requests are served by
conventional MDL_lock data structures.

Strictly speaking moving tickets from fast lanes to conventional
MDL_lock data structures is not required. But it allows to reduce
complexity and keep intact methods like: MDL_lock::visit_subgraph(),
MDL_lock::notify_conflicting_locks(), MDL_lock::reschedule_waiters(),
MDL_lock::can_grant_lock().

It is not even required to register tickets in fast lanes. They
can be implemented basing on an atomic variable that holds two
counters: granted lightweight locks and granted/waiting heavyweight
locks. Similarly to MySQL solution, which roughly speaking has
"single atomic fast lane". However it appears to be it won't bring
any better performance, while code complexity is going to be much
higher.
2025-07-15 23:19:06 +04:00

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/* Copyright (c) 2007, 2012, Oracle and/or its affiliates.
Copyright (c) 2020, 2022, MariaDB
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; version 2 of the License.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software Foundation,
51 Franklin Street, Fifth Floor, Boston, MA 02110-1335 USA */
#include "mariadb.h"
#include "sql_class.h"
#include "debug_sync.h"
#include "sql_array.h"
#include "rpl_rli.h"
#include <lf.h>
#include "aligned.h"
#include "unireg.h"
#include <mysql/plugin.h>
#include <mysql/service_thd_wait.h>
#include <mysql/psi/mysql_stage.h>
#include <tpool.h>
#include <pfs_metadata_provider.h>
#include <mysql/psi/mysql_mdl.h>
#include <algorithm>
#include <array>
#ifdef WITH_WSREP
#include "wsrep_mysqld.h"
#endif
static PSI_memory_key key_memory_MDL_context_acquire_locks;
#ifdef HAVE_PSI_INTERFACE
static PSI_mutex_key key_MDL_lock_fast_lane_mutex;
static PSI_mutex_key key_MDL_wait_LOCK_wait_status;
static PSI_mutex_info all_mdl_mutexes[]=
{
{ &key_MDL_lock_fast_lane_mutex, "MDL_lock::Fast_road::Lane::m_mutex", 0 },
{ &key_MDL_wait_LOCK_wait_status, "MDL_wait::LOCK_wait_status", 0}
};
static PSI_rwlock_key key_MDL_lock_rwlock;
static PSI_rwlock_key key_MDL_context_LOCK_waiting_for;
static PSI_rwlock_info all_mdl_rwlocks[]=
{
{ &key_MDL_lock_rwlock, "MDL_lock::rwlock", 0},
{ &key_MDL_context_LOCK_waiting_for, "MDL_context::LOCK_waiting_for", 0}
};
static PSI_cond_key key_MDL_wait_COND_wait_status;
static PSI_cond_info all_mdl_conds[]=
{
{ &key_MDL_wait_COND_wait_status, "MDL_context::COND_wait_status", 0}
};
static PSI_memory_info all_mdl_memory[]=
{
{ &key_memory_MDL_context_acquire_locks, "MDL_context::acquire_locks", 0}
};
/**
Initialise all the performance schema instrumentation points
used by the MDL subsystem.
*/
static void init_mdl_psi_keys(void)
{
int count;
count= array_elements(all_mdl_mutexes);
mysql_mutex_register("sql", all_mdl_mutexes, count);
count= array_elements(all_mdl_rwlocks);
mysql_rwlock_register("sql", all_mdl_rwlocks, count);
count= array_elements(all_mdl_conds);
mysql_cond_register("sql", all_mdl_conds, count);
count= array_elements(all_mdl_memory);
mysql_memory_register("sql", all_mdl_memory, count);
MDL_key::init_psi_keys();
}
#endif /* HAVE_PSI_INTERFACE */
/**
Thread state names to be used in case when we have to wait on resource
belonging to certain namespace.
*/
PSI_stage_info MDL_key::m_namespace_to_wait_state_name[NAMESPACE_END]=
{
{0, "Waiting for backup lock", 0},
{0, "Waiting for schema metadata lock", 0},
{0, "Waiting for table metadata lock", 0},
{0, "Waiting for stored function metadata lock", 0},
{0, "Waiting for stored procedure metadata lock", 0},
{0, "Waiting for stored package body metadata lock", 0},
{0, "Waiting for trigger metadata lock", 0},
{0, "Waiting for event metadata lock", 0},
{0, "User lock", 0} /* Be compatible with old status. */
};
static const LEX_STRING lock_types[]=
{
{ C_STRING_WITH_LEN("MDL_INTENTION_EXCLUSIVE") },
{ C_STRING_WITH_LEN("MDL_SHARED") },
{ C_STRING_WITH_LEN("MDL_SHARED_HIGH_PRIO") },
{ C_STRING_WITH_LEN("MDL_SHARED_READ") },
{ C_STRING_WITH_LEN("MDL_SHARED_WRITE") },
{ C_STRING_WITH_LEN("MDL_SHARED_UPGRADABLE") },
{ C_STRING_WITH_LEN("MDL_SHARED_READ_ONLY") },
{ C_STRING_WITH_LEN("MDL_SHARED_NO_WRITE") },
{ C_STRING_WITH_LEN("MDL_SHARED_NO_READ_WRITE") },
{ C_STRING_WITH_LEN("MDL_EXCLUSIVE") },
};
static const LEX_STRING backup_lock_types[]=
{
{ C_STRING_WITH_LEN("MDL_BACKUP_START") },
{ C_STRING_WITH_LEN("MDL_BACKUP_FLUSH") },
{ C_STRING_WITH_LEN("MDL_BACKUP_WAIT_FLUSH") },
{ C_STRING_WITH_LEN("MDL_BACKUP_WAIT_DDL") },
{ C_STRING_WITH_LEN("MDL_BACKUP_WAIT_COMMIT") },
{ C_STRING_WITH_LEN("MDL_BACKUP_FTWRL1") },
{ C_STRING_WITH_LEN("MDL_BACKUP_FTWRL2") },
{ C_STRING_WITH_LEN("MDL_BACKUP_DML") },
{ C_STRING_WITH_LEN("MDL_BACKUP_TRANS_DML") },
{ C_STRING_WITH_LEN("MDL_BACKUP_SYS_DML") },
{ C_STRING_WITH_LEN("MDL_BACKUP_DDL") },
{ C_STRING_WITH_LEN("MDL_BACKUP_BLOCK_DDL") },
{ C_STRING_WITH_LEN("MDL_BACKUP_ALTER_COPY") },
{ C_STRING_WITH_LEN("MDL_BACKUP_COMMIT") }
};
#ifdef HAVE_PSI_INTERFACE
void MDL_key::init_psi_keys()
{
int i;
int count;
PSI_stage_info *info __attribute__((unused));
count= array_elements(MDL_key::m_namespace_to_wait_state_name);
for (i= 0; i<count; i++)
{
/* mysql_stage_register wants an array of pointers, registering 1 by 1. */
info= & MDL_key::m_namespace_to_wait_state_name[i];
mysql_stage_register("sql", &info, 1);
}
}
#endif
static bool mdl_initialized= 0;
uint mdl_instances;
enum tal_status { TAL_ERROR, TAL_ACQUIRED, TAL_WAIT, TAL_NOWAIT };
/**
A collection of all MDL locks. A singleton,
there is only one instance of the map in the server.
*/
class MDL_map
{
public:
void init();
void destroy();
enum tal_status try_acquire_lock(LF_PINS *pins, MDL_key *key,
MDL_ticket *ticket, bool wait);
unsigned long get_lock_owner(LF_PINS *pins, const MDL_key *key);
void remove(LF_PINS *pins, const MDL_key *key)
{ lf_hash_delete(&m_locks, pins, key->ptr(), key->length()); }
LF_PINS *get_pins() { return lf_hash_get_pins(&m_locks); }
private:
LF_HASH m_locks; /**< All acquired locks in the server. */
/** Pre-allocated MDL_lock object for BACKUP namespace. */
MDL_lock *m_backup_lock;
friend int mdl_iterate(mdl_iterator_callback, void *);
};
/**
A context of the recursive traversal through all contexts
in all sessions in search for deadlock.
*/
class Deadlock_detection_visitor: public MDL_wait_for_graph_visitor
{
public:
Deadlock_detection_visitor(MDL_context *start_node_arg)
: m_start_node(start_node_arg),
m_victim(NULL),
m_current_search_depth(0),
m_found_deadlock(FALSE)
{}
bool enter_node(MDL_context *node) override;
void leave_node(MDL_context *node) override;
bool inspect_edge(MDL_context *dest) override;
MDL_context *get_victim() const { return m_victim; }
private:
/**
Change the deadlock victim to a new one if it has lower deadlock
weight.
*/
void opt_change_victim_to(MDL_context *new_victim);
private:
/**
The context which has initiated the search. There
can be multiple searches happening in parallel at the same time.
*/
MDL_context *m_start_node;
/** If a deadlock is found, the context that identifies the victim. */
MDL_context *m_victim;
/** Set to the 0 at start. Increased whenever
we descend into another MDL context (aka traverse to the next
wait-for graph node). When MAX_SEARCH_DEPTH is reached, we
assume that a deadlock is found, even if we have not found a
loop.
*/
uint m_current_search_depth;
/** TRUE if we found a deadlock. */
bool m_found_deadlock;
/**
Maximum depth for deadlock searches. After this depth is
achieved we will unconditionally declare that there is a
deadlock.
@note This depth should be small enough to avoid stack
being exhausted by recursive search algorithm.
TODO: Find out what is the optimal value for this parameter.
Current value is safe, but probably sub-optimal,
as there is an anecdotal evidence that real-life
deadlocks are even shorter typically.
*/
static const uint MAX_SEARCH_DEPTH= 32;
};
#ifndef DBUG_OFF
/*
Print a list of all locks to DBUG trace to help with debugging
*/
const char *dbug_print_mdl(MDL_ticket *mdl_ticket)
{
thread_local char buffer[256];
const MDL_key *mdl_key= mdl_ticket->get_key();
my_snprintf(buffer, sizeof(buffer) - 1, "%.*s/%.*s (%s)",
(int) mdl_key->db_name_length(), mdl_key->db_name(),
(int) mdl_key->name_length(), mdl_key->name(),
mdl_ticket->get_type_name()->str);
return buffer;
}
const char *dbug_print(MDL_ticket *mdl_ticket)
{
return dbug_print_mdl(mdl_ticket);
}
static int mdl_dbug_print_lock(MDL_ticket *mdl_ticket, void *arg, bool granted)
{
String *tmp= (String*) arg;
char buffer[256];
size_t length= my_snprintf(buffer, sizeof(buffer) - 1,
"\n %s (%s)", dbug_print_mdl(mdl_ticket),
granted ? "granted" : "waiting");
tmp->append(buffer, length);
return 0;
}
const char *mdl_dbug_print_locks()
{
thread_local String tmp;
tmp.length(0);
mdl_iterate(mdl_dbug_print_lock, (void*) &tmp);
return tmp.c_ptr();
}
#endif /* DBUG_OFF */
/**
Enter a node of a wait-for graph. After
a node is entered, inspect_edge() will be called
for all wait-for destinations of this node. Then
leave_node() will be called.
We call "enter_node()" for all nodes we inspect,
including the starting node.
@retval TRUE Maximum search depth exceeded.
@retval FALSE OK.
*/
bool Deadlock_detection_visitor::enter_node(MDL_context *node)
{
m_found_deadlock= ++m_current_search_depth >= MAX_SEARCH_DEPTH;
if (m_found_deadlock)
{
DBUG_ASSERT(! m_victim);
opt_change_victim_to(node);
}
return m_found_deadlock;
}
/**
Done inspecting this node. Decrease the search
depth. If a deadlock is found, and we are
backtracking to the start node, optionally
change the deadlock victim to one with lower
deadlock weight.
*/
void Deadlock_detection_visitor::leave_node(MDL_context *node)
{
--m_current_search_depth;
if (m_found_deadlock)
opt_change_victim_to(node);
}
/**
Inspect a wait-for graph edge from one MDL context to another.
@retval TRUE A loop is found.
@retval FALSE No loop is found.
*/
bool Deadlock_detection_visitor::inspect_edge(MDL_context *node)
{
m_found_deadlock= node == m_start_node;
return m_found_deadlock;
}
/**
Change the deadlock victim to a new one if it has lower deadlock
weight.
@retval new_victim Victim is not changed.
@retval !new_victim New victim became the current.
*/
void
Deadlock_detection_visitor::opt_change_victim_to(MDL_context *new_victim)
{
if (m_victim == NULL ||
m_victim->get_deadlock_weight() >= new_victim->get_deadlock_weight())
{
/* Swap victims, unlock the old one. */
MDL_context *tmp= m_victim;
m_victim= new_victim;
m_victim->lock_deadlock_victim();
if (tmp)
tmp->unlock_deadlock_victim();
}
}
/**
The lock context. Created internally for an acquired lock.
For a given name, there exists only one MDL_lock instance,
and it exists only when the lock has been granted.
Can be seen as an MDL subsystem's version of TABLE_SHARE.
This is an abstract class which lacks information about
compatibility rules for lock types. They should be specified
in its descendants.
*/
class MDL_lock
{
typedef mdl_bitmap_t bitmap_t;
class Ticket_list
{
using List= ilist<MDL_ticket>;
public:
Ticket_list() :m_bitmap(0) { m_type_counters.fill(0); }
void add_ticket(MDL_ticket *ticket);
void remove_ticket(MDL_ticket *ticket);
bool is_empty() const { return m_list.empty(); }
bitmap_t bitmap() const { return m_bitmap; }
List::const_iterator begin() const { return m_list.begin(); }
List::const_iterator end() const { return m_list.end(); }
private:
/** List of tickets. */
List m_list;
/** Bitmap of types of tickets in this list. */
bitmap_t m_bitmap;
std::array<uint32_t, MDL_BACKUP_END> m_type_counters; // hash table
};
/**
Helper struct which defines how different types of locks are handled
for a specific MDL_lock. In practice we use only three strategies:
"backup" lock strategy for locks in BACKUP namespace, "scoped" lock
strategy for locks in SCHEMA namespace and "object" lock strategy for
all other namespaces.
*/
struct MDL_lock_strategy
{
virtual const bitmap_t *incompatible_granted_types_bitmap() const = 0;
virtual const bitmap_t *incompatible_waiting_types_bitmap() const = 0;
virtual bool needs_notification(const MDL_ticket *ticket) const = 0;
virtual bool conflicting_locks(const MDL_ticket *ticket) const = 0;
virtual bitmap_t hog_lock_types_bitmap() const = 0;
virtual ~MDL_lock_strategy() = default;
};
/**
An implementation of the scoped metadata lock. The only locking modes
which are supported at the moment are SHARED and INTENTION EXCLUSIVE
and EXCLUSIVE
*/
struct MDL_scoped_lock : public MDL_lock_strategy
{
MDL_scoped_lock() = default;
const bitmap_t *incompatible_granted_types_bitmap() const override
{ return m_granted_incompatible; }
const bitmap_t *incompatible_waiting_types_bitmap() const override
{ return m_waiting_incompatible; }
bool needs_notification(const MDL_ticket *ticket) const override
{ return (ticket->get_type() == MDL_SHARED); }
/**
Notify threads holding scoped IX locks which conflict with a pending
S lock.
Thread which holds global IX lock can be a handler thread for
insert delayed. We need to kill such threads in order to get
global shared lock. We do this my calling code outside of MDL.
*/
bool conflicting_locks(const MDL_ticket *ticket) const override
{ return ticket->get_type() == MDL_INTENTION_EXCLUSIVE; }
/*
In scoped locks, only IX lock request would starve because of X/S. But that
is practically very rare case. So just return 0 from this function.
*/
bitmap_t hog_lock_types_bitmap() const override
{ return 0; }
private:
static const bitmap_t m_granted_incompatible[MDL_TYPE_END];
static const bitmap_t m_waiting_incompatible[MDL_TYPE_END];
};
/**
An implementation of a per-object lock. Supports SHARED, SHARED_UPGRADABLE,
SHARED HIGH PRIORITY and EXCLUSIVE locks.
*/
struct MDL_object_lock : public MDL_lock_strategy
{
MDL_object_lock() = default;
const bitmap_t *incompatible_granted_types_bitmap() const override
{ return m_granted_incompatible; }
const bitmap_t *incompatible_waiting_types_bitmap() const override
{ return m_waiting_incompatible; }
bool needs_notification(const MDL_ticket *ticket) const override
{
return (MDL_BIT(ticket->get_type()) &
(MDL_BIT(MDL_SHARED_NO_WRITE) |
MDL_BIT(MDL_SHARED_NO_READ_WRITE) |
MDL_BIT(MDL_EXCLUSIVE)));
}
/**
Notify threads holding a shared metadata locks on object which
conflict with a pending X, SNW or SNRW lock.
If thread which holds conflicting lock is waiting on table-level
lock or some other non-MDL resource we might need to wake it up
by calling code outside of MDL.
*/
bool conflicting_locks(const MDL_ticket *ticket) const override
{ return ticket->get_type() < MDL_SHARED_UPGRADABLE; }
/*
To prevent starvation, these lock types that are only granted
max_write_lock_count times in a row while other lock types are
waiting.
*/
bitmap_t hog_lock_types_bitmap() const override
{
return (MDL_BIT(MDL_SHARED_NO_WRITE) |
MDL_BIT(MDL_SHARED_NO_READ_WRITE) |
MDL_BIT(MDL_EXCLUSIVE));
}
private:
static const bitmap_t m_granted_incompatible[MDL_TYPE_END];
static const bitmap_t m_waiting_incompatible[MDL_TYPE_END];
};
struct MDL_backup_lock: public MDL_lock_strategy
{
MDL_backup_lock() = default;
const bitmap_t *incompatible_granted_types_bitmap() const override
{ return m_granted_incompatible; }
const bitmap_t *incompatible_waiting_types_bitmap() const override
{ return m_waiting_incompatible; }
bool needs_notification(const MDL_ticket *ticket) const override
{
return (MDL_BIT(ticket->get_type()) & MDL_BIT(MDL_BACKUP_FTWRL1));
}
/**
Insert delayed threads may hold DML or TRANS_DML lock.
We need to kill such threads in order to get lock for FTWRL statements.
We do this by calling code outside of MDL.
*/
bool conflicting_locks(const MDL_ticket *ticket) const override
{
return (MDL_BIT(ticket->get_type()) &
(MDL_BIT(MDL_BACKUP_DML) |
MDL_BIT(MDL_BACKUP_TRANS_DML)));
}
/*
In backup namespace DML/DDL may starve because of concurrent FTWRL or
BACKUP statements. This scenario is practically useless in real world,
so we just return 0 here.
*/
bitmap_t hog_lock_types_bitmap() const override
{ return 0; }
private:
static const bitmap_t m_granted_incompatible[MDL_BACKUP_END];
static const bitmap_t m_waiting_incompatible[MDL_BACKUP_END];
};
/**
Scalable handler for "lightweight" lock types.
*/
class Fast_road
{
class Lane
{
alignas(CPU_LEVEL1_DCACHE_LINESIZE) mutable mysql_mutex_t m_mutex;
ilist<MDL_ticket> m_list;
/**
Counts number of granted/pending non-fast lane locks.
Having it as a member of Lane allows simpler and cleaner
implementation. Otherwise it is a property of Fast_road.
*/
uint32_t m_close_count;
bool is_open() const { return m_close_count == 0; }
/**
upgrade/downgrade/release helper.
ticket->m_fast_lane has to be double checked under fast lane mutex
protection. Description in a comment to MDL_lock::release().
@retval true Requested action performed
@retval false Lane closed, try conventional action
*/
template <typename Functor>
bool ticket_action(MDL_ticket *ticket, Functor action)
{
mysql_mutex_lock(&m_mutex);
DBUG_ASSERT(is_open() || m_list.empty());
Lane *lane= static_cast<Lane *>(
ticket->m_fast_lane.load(std::memory_order_relaxed));
if (likely(lane))
{
DBUG_ASSERT(is_open());
DBUG_ASSERT(lane == this);
action();
}
mysql_mutex_unlock(&m_mutex);
return lane != nullptr;
}
public:
Lane() noexcept: m_close_count(0)
{
mysql_mutex_init(key_MDL_lock_fast_lane_mutex, &m_mutex,
MY_MUTEX_INIT_FAST);
}
~Lane()
{
DBUG_ASSERT(m_close_count <= 1);
DBUG_ASSERT(m_list.empty());
mysql_mutex_destroy(&m_mutex);
}
static void *operator new[](size_t size, const std::nothrow_t)
{
return aligned_malloc(size, CPU_LEVEL1_DCACHE_LINESIZE);
}
static void operator delete[](void *ptr) { aligned_free(ptr); }
/**
Registers ticket in fast lane.
ticket->m_fast_lane has to be updated to point to this lane
either before critical section or inside critical section.
Before other threads can find it via m_list.
In most cases this method is called with open fast lane,
when there're no heavyweight locks in this MDL_lock. There is
no point in attempting to avoid mutex lock for closed lanes
by pre-checking lane_open().
@retval true Lock granted
@retval false Lane closed, try conventional lock
*/
bool try_acquire_lock(MDL_ticket *ticket)
{
DBUG_ASSERT(!ticket->m_fast_lane.load(std::memory_order_relaxed));
mysql_mutex_lock(&m_mutex);
bool res= is_open();
DBUG_ASSERT(res || m_list.empty());
if (likely(res))
{
m_list.push_back(*ticket);
ticket->m_fast_lane.store(this, std::memory_order_relaxed);
}
mysql_mutex_unlock(&m_mutex);
return res;
}
/**
Releases previously acquired lock.
@retval true Lock released
@retval false Lane closed, try conventional unlock
*/
bool release(MDL_ticket *ticket)
{
return ticket_action(ticket,
[this, ticket]() { m_list.remove(*ticket); });
}
/**
Updates ticket type.
Used by upgrade/downgrade.
@retval true Success
@retval false Lane closed, try conventional upgrade/downgrade
*/
bool change_ticket_type(MDL_ticket *ticket, enum_mdl_type type)
{
return ticket_action(ticket,
[ticket, type]() { ticket->m_type= type; });
}
/**
Closes fast lane, moves tickets to MDL_lock::m_granted.
Closed fast lane means the following methods have to retry their
action using conventional methods:
MDL_lock::try_acquire_lock()
MDL_lock::release()
MDL_lock::upgrade()
MDL_lock::downgrade()
Lane can be closed multiple times.
*/
void close()
{
mysql_mutex_lock(&m_mutex);
DBUG_ASSERT(is_open() || m_list.empty());
m_close_count++;
while (!m_list.empty())
{
MDL_ticket *ticket= &m_list.front();
m_list.pop_front();
ticket->get_lock()->m_granted.add_ticket(ticket);
DBUG_ASSERT(ticket->m_fast_lane.load(std::memory_order_relaxed) ==
this);
ticket->m_fast_lane.store(nullptr, std::memory_order_relaxed);
}
mysql_mutex_unlock(&m_mutex);
}
/**
Reopens fast lane.
Fast lane can be used again once all closers are gone.
*/
void reopen()
{
mysql_mutex_lock(&m_mutex);
DBUG_ASSERT(m_close_count);
DBUG_ASSERT(m_list.empty());
m_close_count--;
mysql_mutex_unlock(&m_mutex);
}
/**
Iterates registered tickets.
@retval true callback returned true, abort iteration
@retval false success
*/
bool iterate(mdl_iterator_callback callback, void *argument) const
{
bool res= false;
mysql_mutex_lock(&m_mutex);
DBUG_ASSERT(is_open() || m_list.empty());
for (MDL_ticket &ticket : m_list)
{
if (callback(&ticket, argument, true))
{
res= true;
break;
}
}
mysql_mutex_unlock(&m_mutex);
return res;
}
/** Checks if lane is open, used by assertions. */
bool is_closed() const
{
mysql_mutex_lock(&m_mutex);
bool res= !is_open();
mysql_mutex_unlock(&m_mutex);
return res;
}
/** Checks if lane is empty, used by assertions. */
bool is_empty() const
{
mysql_mutex_lock(&m_mutex);
bool res= m_list.empty();
mysql_mutex_unlock(&m_mutex);
return res;
}
};
Lane *m_fast_lane;
mdl_bitmap_t m_supported_types;
/**
Checks if provided lock type can be served by fast lanes.
Fast lane lock types must be fully compatible between each other.
*/
bool supported_type(enum_mdl_type type) const
{
return MDL_BIT(type) & m_supported_types;
}
/**
Checks if ticket is registered in fast lane and performs action().
Another thread can be closing fast lanes concurrently and
resetting ticket->m_fast_lane. To handle such scenario properly
action() has to be double checked ticket->m_fast_lane under fast
lane mutex protection. Accessing ticket->m_fast_lane in this
method is the sole reason it is declared atomic.
@retval true Success
@retval false Failure, try conventional action
*/
template <typename Functor>
bool lane_action(MDL_ticket *ticket, Functor action) const
{
if (Lane *lane= static_cast<Lane *>(
ticket->m_fast_lane.load(std::memory_order_relaxed)))
{
DBUG_ASSERT(is_enabled());
DBUG_ASSERT(supported_type(ticket->get_type()));
if (action(lane))
{
DBUG_ASSERT(supported_type(ticket->get_type()));
return true;
}
}
return false;
}
/**
Iterates available lanes and performs action() for each lane.
@retval true Iteration was aborted by action()
@retval false action() was called for all available lanes successfully
*/
template <typename Functor>
bool all_lanes_action(Functor action) const
{
if (is_enabled())
{
for (uint i= 0; i < mdl_instances; i++)
{
if (action(&m_fast_lane[i]))
return true;
}
}
return false;
}
public:
Fast_road(): m_fast_lane(nullptr), m_supported_types(0) {}
~Fast_road() { delete [] m_fast_lane; }
/**
Enables fast lanes.
Once enabled, supported_types of lock requests can be served via
fast lanes.
*/
void enable(mdl_bitmap_t supported_types)
{
m_fast_lane= mdl_instances > 1 ? new (std::nothrow) Lane[mdl_instances]
: nullptr;
if (m_fast_lane)
m_supported_types= supported_types;
}
bool is_enabled() const { return m_fast_lane; }
/**
Attempts to acquire lock.
@retval true Lock acquired
@retval false request cannot be served by fast lanes,
try conventional acquire_lock
*/
bool try_acquire_lock(MDL_ticket *ticket) const
{
if (is_enabled() && supported_type(ticket->get_type()))
{
DBUG_ASSERT(mdl_instances > 1);
uint lane= ticket->get_ctx()->get_thd()->thread_id % mdl_instances;
return m_fast_lane[lane].try_acquire_lock(ticket);
}
return false;
}
/**
Attempts to release previously acquired lock.
@retval true Lock released
@retval false ticket is not registered in fast lanes,
try conventional unlock
*/
bool try_release(MDL_ticket *ticket) const
{
return lane_action(
ticket, [ticket](Lane *lane) { return lane->release(ticket); });
}
/**
Attempts to upgrade or downgrade lock.
@retval true Lock upgraded/downgraded
@retval false request cannot be served by fast lanes,
try conventional acquire_lock
*/
bool try_change_ticket_type(MDL_ticket *ticket, enum_mdl_type type) const
{
DBUG_ASSERT(supported_type(ticket->get_type()) || is_closed());
return lane_action(ticket,
[ticket, type](Lane *lane)
{ return lane->change_ticket_type(ticket, type); });
}
void close(enum_mdl_type type) const
{
if (!supported_type(type))
all_lanes_action([](Lane *lane) { lane->close(); return false; });
}
void reopen(enum_mdl_type type) const
{
if (!supported_type(type))
all_lanes_action([](Lane *lane) { lane->reopen(); return false; });
}
/**
Iterates registered tickets.
@retval true callback returned true, abort iteration
@retval false success
*/
bool iterate(mdl_iterator_callback callback, void *argument) const
{
return all_lanes_action([callback, argument](Lane *lane)
{ return lane->iterate(callback, argument); });
}
/** Checks if fast lanes are closed, used by assertions. */
bool is_closed() const
{
return !all_lanes_action([](Lane *lane) { return !lane->is_closed(); });
}
/** Checks if fast lanes are empty, used by assertions. */
bool is_empty() const
{
return !all_lanes_action([](Lane *lane) { return !lane->is_empty(); });
}
};
/** The key of the object (data) being protected. */
MDL_key key;
/**
Read-write lock protecting this lock context.
@note The fact that we use read-write lock prefers readers here is
important as deadlock detector won't work correctly otherwise.
For example, imagine that we have following waiters graph:
ctxA -> obj1 -> ctxB -> obj1 -|
^ |
|----------------------------|
and both ctxA and ctxB start deadlock detection process:
ctxA read-locks obj1 ctxB read-locks obj2
ctxA goes deeper ctxB goes deeper
Now ctxC comes in who wants to start waiting on obj1, also
ctxD comes in who wants to start waiting on obj2.
ctxC tries to write-lock obj1 ctxD tries to write-lock obj2
ctxC is blocked ctxD is blocked
Now ctxA and ctxB resume their search:
ctxA tries to read-lock obj2 ctxB tries to read-lock obj1
If m_rwlock prefers writes (or fair) both ctxA and ctxB would be
blocked because of pending write locks from ctxD and ctxC
correspondingly. Thus we will get a deadlock in deadlock detector.
If m_wrlock prefers readers (actually ignoring pending writers is
enough) ctxA and ctxB will continue and no deadlock will occur.
*/
mutable mysql_prlock_t m_rwlock;
/** List of granted tickets for this lock. */
Ticket_list m_granted;
/** Tickets for contexts waiting to acquire a lock. */
Ticket_list m_waiting;
/**
Number of times high priority lock requests have been granted while
low priority lock requests were waiting.
*/
ulong m_hog_lock_count;
Fast_road m_fast_road;
/**
Locking strategy, e.g. backup/scoped/object.
Initialized to appropriate strategy early, before lock becomes
available via MDL_map. Reset to nullptr before lock is removed
from MDL_map. Such value indicates that MDL_lock is being removed
by a concurrent thread and the caller (specifically
MDL_map::try_acquire_lock()) must retry.
*/
const MDL_lock_strategy *m_strategy;
static const MDL_backup_lock m_backup_lock_strategy;
static const MDL_scoped_lock m_scoped_lock_strategy;
static const MDL_object_lock m_object_lock_strategy;
bool is_empty() const
{
return (m_granted.is_empty() && m_waiting.is_empty());
}
bool can_grant_lock(enum_mdl_type type, MDL_context *requstor_ctx,
bool ignore_lock_priority) const;
void reschedule_waiters();
void remove_ticket(LF_PINS *pins, Ticket_list MDL_lock::*queue,
MDL_ticket *ticket);
void notify_conflicting_locks(MDL_context *ctx, bool abort_blocking)
{
DBUG_ASSERT(m_fast_road.is_closed());
for (const auto &conflicting_ticket : m_granted)
{
if (conflicting_ticket.get_ctx() != ctx &&
m_strategy->conflicting_locks(&conflicting_ticket))
{
MDL_context *conflicting_ctx= conflicting_ticket.get_ctx();
ctx->get_owner()->
notify_shared_lock(conflicting_ctx->get_owner(),
conflicting_ctx->get_needs_thr_lock_abort(),
abort_blocking);
}
}
}
#ifndef DBUG_OFF
bool check_if_conflicting_replication_locks(MDL_context *ctx);
#endif
public:
const bitmap_t *incompatible_granted_types_bitmap() const
{ return m_strategy->incompatible_granted_types_bitmap(); }
const bitmap_t *incompatible_waiting_types_bitmap() const
{ return m_strategy->incompatible_waiting_types_bitmap(); }
/**
Check if we have any pending locks which conflict with existing
shared lock.
@pre The ticket must match an acquired lock.
@return TRUE if there is a conflicting lock request, FALSE otherwise.
*/
bool has_pending_conflicting_lock(enum_mdl_type type)
{
bool result;
DBUG_ASSERT(key.mdl_namespace() == MDL_key::TABLE);
DBUG_ASSERT(!m_fast_road.is_enabled());
mysql_prlock_rdlock(&m_rwlock);
result= (m_waiting.bitmap() & incompatible_granted_types_bitmap()[type]);
mysql_prlock_unlock(&m_rwlock);
return result;
}
bool visit_subgraph(MDL_ticket *waiting_ticket,
MDL_wait_for_graph_visitor *gvisitor);
MDL_lock()
: m_hog_lock_count(0),
m_strategy(0)
{ mysql_prlock_init(key_MDL_lock_rwlock, &m_rwlock); }
MDL_lock(const MDL_key *key_arg)
: key(key_arg),
m_hog_lock_count(0),
m_strategy(&m_backup_lock_strategy)
{
DBUG_ASSERT(key_arg->mdl_namespace() == MDL_key::BACKUP);
mysql_prlock_init(key_MDL_lock_rwlock, &m_rwlock);
m_fast_road.enable(MDL_BIT(MDL_BACKUP_DML) |
MDL_BIT(MDL_BACKUP_TRANS_DML) |
MDL_BIT(MDL_BACKUP_SYS_DML) |
MDL_BIT(MDL_BACKUP_DDL) |
MDL_BIT(MDL_BACKUP_ALTER_COPY) |
MDL_BIT(MDL_BACKUP_COMMIT));
}
~MDL_lock()
{ mysql_prlock_destroy(&m_rwlock); }
static void lf_alloc_constructor(uchar *arg)
{ new (arg + LF_HASH_OVERHEAD) MDL_lock(); }
static void lf_alloc_destructor(uchar *arg)
{ ((MDL_lock*)(arg + LF_HASH_OVERHEAD))->~MDL_lock(); }
static void lf_hash_initializer(LF_HASH *hash __attribute__((unused)),
void *_lock, const void *_key_arg)
{
MDL_lock *lock= static_cast<MDL_lock *>(_lock);
const MDL_key *key_arg= static_cast<const MDL_key *>(_key_arg);
DBUG_ASSERT(key_arg->mdl_namespace() != MDL_key::BACKUP);
new (&lock->key) MDL_key(key_arg);
if (key_arg->mdl_namespace() == MDL_key::SCHEMA)
lock->m_strategy= &m_scoped_lock_strategy;
else
lock->m_strategy= &m_object_lock_strategy;
}
static const uchar *mdl_locks_key(const void *record, size_t *length,
my_bool)
{
const MDL_lock *lock= static_cast<const MDL_lock *>(record);
*length= lock->key.length();
return lock->key.ptr();
}
/**
Return thread id of the thread to which the first ticket was
granted.
Intended for user level locks. They make use of SNW lock only,
thus there can be only one granted ticket.
We can skip check for m_strategy here, because m_granted
must be empty for such locks anyway.
*/
unsigned long get_lock_owner() const
{
unsigned long res= 0;
DBUG_ASSERT(key.mdl_namespace() == MDL_key::USER_LOCK);
DBUG_ASSERT(!m_fast_road.is_enabled());
mysql_prlock_rdlock(&m_rwlock);
DBUG_ASSERT(m_strategy || is_empty());
if (!m_granted.is_empty())
res= m_granted.begin()->get_ctx()->get_thread_id();
mysql_prlock_unlock(&m_rwlock);
return res;
}
/**
Callback for mdl_iterate()
Another thread may be deleting this MDL_lock concurrently.
Being deleted lock can still be iterated since it must have
valid empty granted/waiting lists.
Iterate fast lanes first, then go for conventional m_granted
and m_waiting lists. To make MDL_lock snapshot consistent, fast
lanes iteration has to be performed under m_rwlock protection.
Strictly speaking fast lanes iteration alone doesn't require
m_rwlock protection. However another thread may be moving the
ticket from fast lane to m_granted list concurrently.
If fast lanes are iterated before m_rwlock critical section,
then ticket iterator may see this ticket twice: once from fast
lane and once from m_granted list.
If fast lanes are iterated after m_rwlock critical section,
then ticket iterator may miss this ticket: it can be removed
from fast lane, but not yet inserted to m_granted list.
@retval true callback returned true, abort iteration
@retval false success
*/
bool iterate(mdl_iterator_callback callback, void *argument)
{
bool res= true;
mysql_prlock_rdlock(&m_rwlock);
DBUG_ASSERT(m_strategy || is_empty());
DBUG_ASSERT(m_strategy || m_fast_road.is_empty());
if (m_fast_road.iterate(callback, argument))
goto end;
for (MDL_ticket &ticket : m_granted)
{
if (callback(&ticket, argument, true))
goto end;
}
for (MDL_ticket &ticket : m_waiting)
{
if (callback(&ticket, argument, false))
goto end;
}
res= false;
end:
mysql_prlock_unlock(&m_rwlock);
return res;
}
/**
MDL_context::clone_ticket() helper
Cloned tickets don't seem to be used by performance critical
code, so they're always added to conventional m_granted list.
Support for fast lanes can be trivially implemented if needed.
*/
void add_cloned_ticket(MDL_ticket *ticket)
{
m_fast_road.close(ticket->get_type());
mysql_prlock_wrlock(&m_rwlock);
m_granted.add_ticket(ticket);
mysql_prlock_unlock(&m_rwlock);
}
/**
MDL_context::downgrade_lock() helper
To update state of MDL_lock object correctly we need to temporarily
exclude ticket from the granted queue and then include it back.
fast lane lock types can only be downgraded to weaker fast lane
lock types. non-fast lane lock types can only be downgraded to
weaker non-fast lane lock types.
Note that we don't have to reschedule_waiters() when we perform
downgrade via m_fast_road. There can't be any waiters in such case.
*/
void downgrade(MDL_ticket *ticket, enum_mdl_type type)
{
if (m_fast_road.try_change_ticket_type(ticket, type))
return;
mysql_prlock_wrlock(&m_rwlock);
m_granted.remove_ticket(ticket);
ticket->m_type= type;
m_granted.add_ticket(ticket);
reschedule_waiters();
mysql_prlock_unlock(&m_rwlock);
}
/**
MDL_context::upgrade_shared_lock() helper
To update state of MDL_lock object correctly we need to temporarily
exclude ticket from the granted queue and then include it back.
fast lane lock types can only be upgraded to stronger fast lane
lock types. non-fast lane lock types can only be upgraded to
stronger non-fast lane lock types.
Non-fast lane locks close fast lanes whenever they're registered in
MDL_lock. Whenever such locks are being deregistered, fast lanes must
be reopened. Once all closers are gone, that is number of close calls
equals to number of open calls, fast lanes become available again.
*/
void upgrade(MDL_ticket *ticket, enum_mdl_type type,
MDL_ticket *remove)
{
DBUG_ASSERT(!ticket->m_fast_lane.load(std::memory_order_relaxed));
mysql_prlock_wrlock(&m_rwlock);
if (remove && !m_fast_road.try_release(remove))
{
m_fast_road.reopen(remove->get_type());
m_granted.remove_ticket(remove);
}
m_granted.remove_ticket(ticket);
ticket->m_type= type;
m_granted.add_ticket(ticket);
mysql_prlock_unlock(&m_rwlock);
}
bool try_fast_upgrade(MDL_ticket *ticket, enum_mdl_type type)
{
return m_fast_road.try_change_ticket_type(ticket, type);
}
void notify_conflicting_locks_if_needed(MDL_ticket *ticket, bool abort_blocking)
{
if (m_strategy->needs_notification(ticket))
{
mysql_prlock_wrlock(&m_rwlock);
notify_conflicting_locks(ticket->get_ctx(), abort_blocking);
mysql_prlock_unlock(&m_rwlock);
}
}
/**
Attempt to acquire lock
Before performing any action we must ensure that this lock
is not being deleted by concurrent thread. We're safe when
m_strategy != nullptr.
When there're no conflicting granted/waiting locks, lock request
can be served immediately. In this case the only action that has
to be performed is adding ticket to m_granted list.
If it is impossible to serve lock request immediately and the caller
doesn't intend to wait for this lock, no action has to be performed.
This is the case for MDL_context::acquire_lock() with
lock_wait_timeout == 0 and MDL_context::try_acquire_lock().
Otherwise it is regular MDL_context::acquire_lock(). Add ticket
to m_waiting list and notify conflicting lock owners.
Also assert that if we are trying to get an exclusive lock for a slave
running parallel replication, then we are not blocked by another
parallel slave thread that is not committed. This should never happen as
the parallel replication scheduler should never schedule a DDL while
DML's are still running.
ticket->m_lock has to be updated to point to this lock either before
critical section or inside critical section. Before other threads can
find it via m_granted or m_waiting lists.
ticket->m_lock is valid only when this method returns either TAL_ACQUIRED
or TAL_WAIT. In other cases caller doesn't hold references to this lock,
which means it can be detroyed. Caller is expected to dispose ticket
immediately anyway.
Certain lock requests can be served by multi-instance scalable fast lanes.
The following requirements must be met to make it happen: fast lanes must
be enabled for this MDL_lock, fast lanes must be open and lock request
type must satisfy Fast_road::supported_type().
Fast lanes are available for certain namespaces, e.g. initial implementation
supported only BACKUP namespace and when fast lanes were allocated
successfully.
Non-fast lane lock requests are never served by fast lanes. Such lock
requests close all fast lanes and move fast lane tickets to conventional
MDL_lock::m_granted list. Fast lanes are reopened once all such locks are
released or aborted.
@retval TAL_ACQUIRED Acquired
@retval TAL_WAIT Not acquired, must be waited
@retval TAL_NOWAIT Not acquired, cannot be waited
@retval TAL_ERROR Lock is being deleted, retry
*/
enum tal_status try_acquire_lock(MDL_ticket *ticket, bool wait)
{
MDL_context *mdl_context= ticket->get_ctx();
// TAL_ACQUIRED to make less work on the hot path
enum tal_status res= TAL_ACQUIRED;
ticket->m_lock= this;
if (m_fast_road.try_acquire_lock(ticket))
return res;
mysql_prlock_wrlock(&m_rwlock);
if (likely(m_strategy))
{
m_fast_road.close(ticket->get_type());
if (can_grant_lock(ticket->get_type(), mdl_context, false))
m_granted.add_ticket(ticket);
else
{
DBUG_ASSERT(!is_empty());
if (wait)
{
res= TAL_WAIT;
m_waiting.add_ticket(ticket);
if (m_strategy->needs_notification(ticket))
notify_conflicting_locks(mdl_context, false);
DBUG_SLOW_ASSERT((ticket->get_type() != MDL_INTENTION_EXCLUSIVE &&
ticket->get_type() != MDL_EXCLUSIVE) ||
!(mdl_context->get_thd()->rgi_slave &&
mdl_context->get_thd()->rgi_slave->is_parallel_exec &&
check_if_conflicting_replication_locks(mdl_context)));
}
else
{
m_fast_road.reopen(ticket->get_type());
res= TAL_NOWAIT;
}
}
}
else
{
DBUG_ASSERT(m_fast_road.is_closed());
res= TAL_ERROR;
}
mysql_prlock_unlock(&m_rwlock);
return res;
}
/**
Releases previously acquired lock.
Lock requests that were served by fast lanes are redirected to fast
lanes. No waiters are possible in this case, there is nobody to awake.
Lock requests that were served by fast lanes, which were closed
in the meantime, are released conventionally.
Conventional lock release consists of removing lock from m_granted
list, awaking waiters and destroying MDL_lock if needed.
*/
void release(LF_PINS *pins, MDL_ticket *ticket)
{
DBUG_ASSERT(key.mdl_namespace() == MDL_key::BACKUP ||
!m_fast_road.is_enabled());
if (m_fast_road.try_release(ticket))
return;
remove_ticket(pins, &MDL_lock::m_granted, ticket);
}
void abort_wait(LF_PINS *pins, MDL_ticket *ticket)
{ remove_ticket(pins, &MDL_lock::m_waiting, ticket); }
const MDL_key *get_key() const { return &key; }
};
const MDL_lock::MDL_backup_lock MDL_lock::m_backup_lock_strategy;
const MDL_lock::MDL_scoped_lock MDL_lock::m_scoped_lock_strategy;
const MDL_lock::MDL_object_lock MDL_lock::m_object_lock_strategy;
static MDL_map mdl_locks;
/**
Initialize the metadata locking subsystem.
This function is called at server startup.
In particular, initializes the new global mutex and
the associated condition variable: LOCK_mdl and COND_mdl.
These locking primitives are implementation details of the MDL
subsystem and are private to it.
*/
void mdl_init()
{
DBUG_ASSERT(! mdl_initialized);
mdl_initialized= TRUE;
#ifdef HAVE_PSI_INTERFACE
init_mdl_psi_keys();
#endif
mdl_locks.init();
}
/**
Release resources of metadata locking subsystem.
Destroys the global mutex and the condition variable.
Called at server shutdown.
*/
void mdl_destroy()
{
if (mdl_initialized)
{
mdl_initialized= FALSE;
mdl_locks.destroy();
}
}
struct mdl_iterate_arg
{
mdl_iterator_callback callback;
void *argument;
};
static my_bool mdl_iterate_lock(void *lk, void *a)
{
MDL_lock *lock= static_cast<MDL_lock*>(lk);
mdl_iterate_arg *arg= static_cast<mdl_iterate_arg*>(a);
return lock->iterate(arg->callback, arg->argument);
}
int mdl_iterate(mdl_iterator_callback callback, void *arg)
{
DBUG_ENTER("mdl_iterate");
mdl_iterate_arg argument= { callback, arg };
int res= 1;
if (LF_PINS *pins= mdl_locks.get_pins())
{
res= mdl_iterate_lock(mdl_locks.m_backup_lock, &argument) ||
lf_hash_iterate(&mdl_locks.m_locks, pins, mdl_iterate_lock,
&argument);
lf_hash_put_pins(pins);
}
DBUG_RETURN(res);
}
my_hash_value_type mdl_hash_function(CHARSET_INFO *cs,
const uchar *key, size_t length)
{
MDL_key *mdl_key= (MDL_key*) (key - offsetof(MDL_key, m_ptr));
return mdl_key->hash_value();
}
/** Initialize the container for all MDL locks. */
void MDL_map::init()
{
MDL_key backup_lock_key(MDL_key::BACKUP, "", "");
m_backup_lock= new (std::nothrow) MDL_lock(&backup_lock_key);
lf_hash_init(&m_locks, sizeof(MDL_lock), LF_HASH_UNIQUE, 0, 0,
MDL_lock::mdl_locks_key, &my_charset_bin);
m_locks.alloc.constructor= MDL_lock::lf_alloc_constructor;
m_locks.alloc.destructor= MDL_lock::lf_alloc_destructor;
m_locks.initializer= MDL_lock::lf_hash_initializer;
m_locks.hash_function= mdl_hash_function;
}
/**
Destroy the container for all MDL locks.
@pre It must be empty.
*/
void MDL_map::destroy()
{
delete m_backup_lock;
DBUG_ASSERT(!lf_hash_size(&m_locks));
lf_hash_destroy(&m_locks);
}
/**
Find MDL_lock object corresponding to the key, create it
if it does not exist.
@retval TAL_ACQUIRED Acquired
@retval TAL_WAIT Not acquired, must be waited
@retval TAL_NOWAIT Not acquired, cannot be waited
@retval TAL_ERROR Failure (OOM)
*/
enum tal_status MDL_map::try_acquire_lock(LF_PINS *pins, MDL_key *mdl_key,
MDL_ticket *ticket,
bool wait)
{
MDL_lock *lock;
if (mdl_key->mdl_namespace() == MDL_key::BACKUP)
{
/*
Use m_backup_lock shortcut. Such optimization allows to save
one hash lookup for any statement changing data.
It works since this namespace contains only one element so keys
for them look like '<namespace-id>\0\0'.
*/
DBUG_ASSERT(mdl_key->length() == 3);
return m_backup_lock->try_acquire_lock(ticket, wait);
}
retry:
while (!(lock= (MDL_lock*) lf_hash_search(&m_locks, pins, mdl_key->ptr(),
mdl_key->length())))
if (lf_hash_insert(&m_locks, pins, (uchar*) mdl_key) == -1)
return TAL_ERROR;
enum tal_status res= lock->try_acquire_lock(ticket, wait);
lf_hash_search_unpin(pins);
if (res == TAL_ERROR)
goto retry;
return res;
}
/**
* Return thread id of the owner of the lock, if it is owned.
*/
unsigned long
MDL_map::get_lock_owner(LF_PINS *pins, const MDL_key *mdl_key)
{
DBUG_ASSERT(mdl_key->mdl_namespace() == MDL_key::USER_LOCK);
if (MDL_lock *lock= (MDL_lock*) lf_hash_search(&m_locks, pins, mdl_key->ptr(),
mdl_key->length()))
{
unsigned long res= lock->get_lock_owner();
lf_hash_search_unpin(pins);
return res;
}
return 0;
}
/**
Initialize a metadata locking context.
This is to be called when a new server connection is created.
*/
MDL_context::MDL_context()
:
m_owner(NULL),
m_needs_thr_lock_abort(FALSE),
m_waiting_for(NULL),
m_pins(NULL)
{
mysql_prlock_init(key_MDL_context_LOCK_waiting_for, &m_LOCK_waiting_for);
}
/**
Destroy metadata locking context.
Assumes and asserts that there are no active or pending locks
associated with this context at the time of the destruction.
Currently does nothing. Asserts that there are no pending
or satisfied lock requests. The pending locks must be released
prior to destruction. This is a new way to express the assertion
that all tables are closed before a connection is destroyed.
*/
void MDL_context::destroy()
{
DBUG_ASSERT(m_tickets[MDL_STATEMENT].is_empty());
DBUG_ASSERT(m_tickets[MDL_TRANSACTION].is_empty());
DBUG_ASSERT(m_tickets[MDL_EXPLICIT].is_empty());
mysql_prlock_destroy(&m_LOCK_waiting_for);
if (m_pins)
lf_hash_put_pins(m_pins);
}
bool MDL_context::fix_pins()
{
return m_pins ? false : (m_pins= mdl_locks.get_pins()) == 0;
}
/**
Initialize a lock request.
This is to be used for every lock request.
Note that initialization and allocation are split into two
calls. This is to allow flexible memory management of lock
requests. Normally a lock request is stored in statement memory
(e.g. is a member of struct TABLE_LIST), but we would also like
to allow allocation of lock requests in other memory roots,
for example in the grant subsystem, to lock privilege tables.
The MDL subsystem does not own or manage memory of lock requests.
@param mdl_namespace Id of namespace of object to be locked
@param db Name of database to which the object belongs
@param name Name of of the object
@param mdl_type The MDL lock type for the request.
*/
void MDL_request::init_with_source(MDL_key::enum_mdl_namespace mdl_namespace,
const char *db_arg,
const char *name_arg,
enum_mdl_type mdl_type_arg,
enum_mdl_duration mdl_duration_arg,
const char *src_file,
uint src_line)
{
key.mdl_key_init(mdl_namespace, db_arg, name_arg);
type= mdl_type_arg;
duration= mdl_duration_arg;
ticket= NULL;
m_src_file= src_file;
m_src_line= src_line;
}
/**
Initialize a lock request using pre-built MDL_key.
@sa MDL_request::init(namespace, db, name, type).
@param key_arg The pre-built MDL key for the request.
@param mdl_type_arg The MDL lock type for the request.
*/
void MDL_request::init_by_key_with_source(const MDL_key *key_arg,
enum_mdl_type mdl_type_arg,
enum_mdl_duration mdl_duration_arg,
const char *src_file,
uint src_line)
{
key.mdl_key_init(key_arg);
type= mdl_type_arg;
duration= mdl_duration_arg;
ticket= NULL;
m_src_file= src_file;
m_src_line= src_line;
}
MDL_ticket::MDL_ticket(MDL_context *ctx_arg, MDL_request *mdl_request):
#ifndef DBUG_OFF
m_duration(mdl_request->duration),
#endif
m_time(0),
m_fast_lane(nullptr),
m_type(mdl_request->type),
m_ctx(ctx_arg),
m_lock(nullptr)
{
m_psi= mysql_mdl_create(this,
&mdl_request->key,
mdl_request->type,
mdl_request->duration,
PENDING,
mdl_request->m_src_file,
mdl_request->m_src_line);
}
MDL_ticket::~MDL_ticket()
{
mysql_mdl_destroy(m_psi);
}
/**
Return the 'weight' of this ticket for the
victim selection algorithm. Requests with
lower weight are preferred to requests
with higher weight when choosing a victim.
*/
uint MDL_ticket::get_deadlock_weight() const
{
if (get_key()->mdl_namespace() == MDL_key::BACKUP)
{
if (m_type == MDL_BACKUP_FTWRL1)
return DEADLOCK_WEIGHT_FTWRL1;
return DEADLOCK_WEIGHT_DDL;
}
return m_type >= MDL_SHARED_UPGRADABLE ?
DEADLOCK_WEIGHT_DDL : DEADLOCK_WEIGHT_DML;
}
/** Construct an empty wait slot. */
MDL_wait::MDL_wait()
:m_wait_status(EMPTY)
{
mysql_mutex_init(key_MDL_wait_LOCK_wait_status, &m_LOCK_wait_status, NULL);
mysql_cond_init(key_MDL_wait_COND_wait_status, &m_COND_wait_status, NULL);
}
/** Destroy system resources. */
MDL_wait::~MDL_wait()
{
mysql_mutex_destroy(&m_LOCK_wait_status);
mysql_cond_destroy(&m_COND_wait_status);
}
/**
Set the status unless it's already set. Return FALSE if set,
TRUE otherwise.
*/
bool MDL_wait::set_status(enum_wait_status status_arg)
{
bool was_occupied= TRUE;
mysql_mutex_lock(&m_LOCK_wait_status);
if (m_wait_status == EMPTY)
{
was_occupied= FALSE;
m_wait_status= status_arg;
mysql_cond_signal(&m_COND_wait_status);
}
mysql_mutex_unlock(&m_LOCK_wait_status);
return was_occupied;
}
/** Query the current value of the wait slot. */
MDL_wait::enum_wait_status MDL_wait::get_status()
{
enum_wait_status result;
mysql_mutex_lock(&m_LOCK_wait_status);
result= m_wait_status;
mysql_mutex_unlock(&m_LOCK_wait_status);
return result;
}
/** Clear the current value of the wait slot. */
void MDL_wait::reset_status()
{
mysql_mutex_lock(&m_LOCK_wait_status);
m_wait_status= EMPTY;
mysql_mutex_unlock(&m_LOCK_wait_status);
}
/**
Wait for the status to be assigned to this wait slot.
@param owner MDL context owner.
@param abs_timeout Absolute time after which waiting should stop.
@param set_status_on_timeout TRUE - If in case of timeout waiting
context should close the wait slot by
sending TIMEOUT to itself.
FALSE - Otherwise.
@param wait_state_name Thread state name to be set for duration of wait.
@returns Signal posted.
*/
MDL_wait::enum_wait_status
MDL_wait::timed_wait(MDL_context_owner *owner, struct timespec *abs_timeout,
bool set_status_on_timeout,
const PSI_stage_info *wait_state_name)
{
PSI_stage_info old_stage;
enum_wait_status result;
int wait_result= 0;
DBUG_ENTER("MDL_wait::timed_wait");
mysql_mutex_lock(&m_LOCK_wait_status);
owner->ENTER_COND(&m_COND_wait_status, &m_LOCK_wait_status,
wait_state_name, & old_stage);
thd_wait_begin(NULL, THD_WAIT_META_DATA_LOCK);
tpool::tpool_wait_begin();
while (!m_wait_status && !owner->is_killed() &&
wait_result != ETIMEDOUT && wait_result != ETIME)
{
#ifdef WITH_WSREP
# ifdef ENABLED_DEBUG_SYNC
// Allow tests to block thread before MDL-wait
DEBUG_SYNC(owner->get_thd(), "wsrep_before_mdl_wait");
# endif
if (WSREP_ON && wsrep_thd_is_BF(owner->get_thd(), false))
{
wait_result= mysql_cond_wait(&m_COND_wait_status, &m_LOCK_wait_status);
}
else
#endif /* WITH_WSREP */
wait_result= mysql_cond_timedwait(&m_COND_wait_status, &m_LOCK_wait_status,
abs_timeout);
}
tpool::tpool_wait_end();
thd_wait_end(NULL);
if (m_wait_status == EMPTY)
{
/*
Wait has ended not due to a status being set from another
thread but due to this connection/statement being killed or a
time out.
To avoid races, which may occur if another thread sets
GRANTED status before the code which calls this method
processes the abort/timeout, we assign the status under
protection of the m_LOCK_wait_status, within the critical
section. An exception is when set_status_on_timeout is
false, which means that the caller intends to restart the
wait.
*/
if (owner->is_killed())
m_wait_status= KILLED;
else if (set_status_on_timeout)
m_wait_status= TIMEOUT;
}
result= m_wait_status;
owner->EXIT_COND(& old_stage);
DBUG_RETURN(result);
}
/**
Add ticket to MDL_lock's list of waiting requests and
update corresponding bitmap of lock types.
*/
void MDL_lock::Ticket_list::add_ticket(MDL_ticket *ticket)
{
/*
Ticket being added to the list must have MDL_ticket::m_lock set,
since for such tickets methods accessing this member might be
called by other threads.
*/
DBUG_ASSERT(ticket->get_lock());
#ifdef WITH_WSREP
if (WSREP_ON && (this == &(ticket->get_lock()->m_waiting)) &&
wsrep_thd_is_BF(ticket->get_ctx()->get_thd(), false))
{
DBUG_ASSERT(WSREP(ticket->get_ctx()->get_thd()));
m_list.insert(std::find_if(ticket->get_lock()->m_waiting.begin(),
ticket->get_lock()->m_waiting.end(),
[](const MDL_ticket &waiting) {
return !wsrep_thd_is_BF(
waiting.get_ctx()->get_thd(), true);
}),
*ticket);
}
else
#endif /* WITH_WSREP */
{
/*
Add ticket to the *back* of the queue to ensure fairness
among requests with the same priority.
*/
m_list.push_back(*ticket);
}
m_bitmap|= MDL_BIT(ticket->get_type());
m_type_counters[ticket->get_type()]++;
}
/**
Remove ticket from MDL_lock's list of requests and
update corresponding bitmap of lock types.
*/
void MDL_lock::Ticket_list::remove_ticket(MDL_ticket *ticket)
{
m_list.remove(*ticket);
/*
Check if waiting queue has another ticket with the same type as
one which was removed. If there is no such ticket, i.e. we have
removed last ticket of particular type, then we need to update
bitmap of waiting ticket's types.
*/
if (--m_type_counters[ticket->get_type()] == 0)
m_bitmap&= ~MDL_BIT(ticket->get_type());
}
/**
Determine waiting contexts which requests for the lock can be
satisfied, grant lock to them and wake them up.
@note Together with MDL_lock::add_ticket() this method implements
fair scheduling among requests with the same priority.
It tries to grant lock from the head of waiters list, while
add_ticket() adds new requests to the back of this list.
*/
void MDL_lock::reschedule_waiters()
{
bool skip_high_priority= false;
bitmap_t hog_lock_types= m_strategy->hog_lock_types_bitmap();
if (m_hog_lock_count >= max_write_lock_count)
{
/*
If number of successively granted high-prio, strong locks has exceeded
max_write_lock_count give a way to low-prio, weak locks to avoid their
starvation.
*/
if ((m_waiting.bitmap() & ~hog_lock_types) != 0)
{
/*
Even though normally when m_hog_lock_count is non-0 there is
some pending low-prio lock, we still can encounter situation
when m_hog_lock_count is non-0 and there are no pending low-prio
locks. This, for example, can happen when a ticket for pending
low-prio lock was removed from waiters list due to timeout,
and reschedule_waiters() is called after that to update the
waiters queue. m_hog_lock_count will be reset to 0 at the
end of this call in such case.
Note that it is not an issue if we fail to wake up any pending
waiters for weak locks in the loop below. This would mean that
all of them are either killed, timed out or chosen as a victim
by deadlock resolver, but have not managed to remove ticket
from the waiters list yet. After tickets will be removed from
the waiters queue there will be another call to
reschedule_waiters() with pending bitmap updated to reflect new
state of waiters queue.
*/
skip_high_priority= true;
}
}
/*
Find the first (and hence the oldest) waiting request which
can be satisfied (taking into account priority). Grant lock to it.
Repeat the process for the remainder of waiters.
Note we don't need to re-start iteration from the head of the
list after satisfying the first suitable request as in our case
all compatible types of requests have the same priority.
TODO/FIXME: We should:
- Either switch to scheduling without priorities
which will allow to stop iteration through the
list of waiters once we found the first ticket
which can't be satisfied
- Or implement some check using bitmaps which will
allow to stop iteration in cases when, e.g., we
grant SNRW lock and there are no pending S or
SH locks.
*/
for (auto it= m_waiting.begin(); it != m_waiting.end(); ++it)
{
/*
Skip high-prio, strong locks if earlier we have decided to give way to
low-prio, weaker locks.
*/
if (skip_high_priority &&
((MDL_BIT(it->get_type()) & hog_lock_types) != 0))
continue;
if (can_grant_lock(it->get_type(), it->get_ctx(),
skip_high_priority))
{
if (!it->get_ctx()->m_wait.set_status(MDL_wait::GRANTED))
{
/*
Satisfy the found request by updating lock structures.
It is OK to do so even after waking up the waiter since any
session which tries to get any information about the state of
this lock has to acquire MDL_lock::m_rwlock first and thus,
when manages to do so, already sees an updated state of the
MDL_lock object.
*/
auto prev_it= std::prev(it); // this might be begin()-- but the hack
// works because list is circular
m_waiting.remove_ticket(&*it);
m_granted.add_ticket(&*it);
/*
Increase counter of successively granted high-priority strong locks,
if we have granted one.
*/
if ((MDL_BIT(it->get_type()) & hog_lock_types) != 0)
m_hog_lock_count++;
it= prev_it;
}
/*
If we could not update the wait slot of the waiter,
it can be due to fact that its connection/statement was
killed or it has timed out (i.e. the slot is not empty).
Since in all such cases the waiter assumes that the lock was
not been granted, we should keep the request in the waiting
queue and look for another request to reschedule.
*/
}
}
if ((m_waiting.bitmap() & ~hog_lock_types) == 0)
{
/*
Reset number of successively granted high-prio, strong locks
if there are no pending low-prio, weak locks.
This ensures:
- That m_hog_lock_count is correctly reset after strong lock
is released and weak locks are granted (or there are no
other lock requests).
- That situation when SNW lock is granted along with some SR
locks, but SW locks are still blocked are handled correctly.
- That m_hog_lock_count is zero in most cases when there are no pending
weak locks (see comment at the start of this method for example of
exception). This allows to save on checks at the start of this method.
*/
m_hog_lock_count= 0;
}
}
/**
Compatibility (or rather "incompatibility") matrices for scoped metadata
lock.
Scoped locks are database (or schema) locks.
Arrays of bitmaps which elements specify which granted/waiting locks
are incompatible with type of lock being requested.
The first array specifies if particular type of request can be satisfied
if there is granted scoped lock of certain type.
(*) Since intention shared scoped locks (IS) are compatible with all other
type of locks, they don't need to be implemented and there is no code
for them.
| Type of active |
Request | scoped lock |
type | IS(*) IX S X |
---------+------------------+
IS(*) | + + + + |
IX | + + - - |
S | + - + - |
X | + - - - |
The second array specifies if particular type of request can be satisfied
if there is already waiting request for the scoped lock of certain type.
I.e. it specifies what is the priority of different lock types.
| Pending |
Request | scoped lock |
type | IS(*) IX S X |
---------+-----------------+
IS(*) | + + + + |
IX | + + - - |
S | + + + - |
X | + + + + |
Here: "+" -- means that request can be satisfied
"-" -- means that request can't be satisfied and should wait
Note that relation between scoped locks and objects locks requested
by statement is not straightforward and is therefore fully defined
by SQL-layer.
For example, in order to support global read lock implementation
SQL-layer acquires IX lock in GLOBAL namespace for each statement
that can modify metadata or data (i.e. for each statement that
needs SW, SU, SNW, SNRW or X object locks). OTOH, to ensure that
DROP DATABASE works correctly with concurrent DDL, IX metadata locks
in SCHEMA namespace are acquired for DDL statements which can update
metadata in the schema (i.e. which acquire SU, SNW, SNRW and X locks
on schema objects) and aren't acquired for DML.
*/
const MDL_lock::bitmap_t
MDL_lock::MDL_scoped_lock::m_granted_incompatible[MDL_TYPE_END]=
{
MDL_BIT(MDL_EXCLUSIVE) | MDL_BIT(MDL_SHARED),
MDL_BIT(MDL_EXCLUSIVE) | MDL_BIT(MDL_INTENTION_EXCLUSIVE),
0, 0, 0, 0, 0, 0, 0,
MDL_BIT(MDL_EXCLUSIVE) | MDL_BIT(MDL_SHARED) | MDL_BIT(MDL_INTENTION_EXCLUSIVE)
};
const MDL_lock::bitmap_t
MDL_lock::MDL_scoped_lock::m_waiting_incompatible[MDL_TYPE_END]=
{
MDL_BIT(MDL_EXCLUSIVE) | MDL_BIT(MDL_SHARED),
MDL_BIT(MDL_EXCLUSIVE), 0, 0, 0, 0, 0, 0, 0, 0
};
/**
Compatibility (or rather "incompatibility") matrices for per-object
metadata lock. Arrays of bitmaps which elements specify which granted/
waiting locks are incompatible with type of lock being requested.
The first array specifies if particular type of request can be satisfied
if there is granted lock of certain type.
Request | Granted requests for lock |
type | S SH SR SW SU SRO SNW SNRW X |
----------+------------------------------------+
S | + + + + + + + + - |
SH | + + + + + + + + - |
SR | + + + + + + + - - |
SW | + + + + + - - - - |
SU | + + + + - + - - - |
SRO | + + + - + + + - - |
SNW | + + + - - + - - - |
SNRW | + + - - - - - - - |
X | - - - - - - - - - |
SU -> X | - - - - 0 - 0 0 0 |
SNW -> X | - - - 0 0 - 0 0 0 |
SNRW -> X | - - 0 0 0 0 0 0 0 |
The second array specifies if particular type of request can be satisfied
if there is waiting request for the same lock of certain type. In other
words it specifies what is the priority of different lock types.
Request | Pending requests for lock |
type | S SH SR SW SU SRO SNW SNRW X |
----------+-----------------------------------+
S | + + + + + + + + - |
SH | + + + + + + + + + |
SR | + + + + + + + - - |
SW | + + + + + + - - - |
SU | + + + + + + + + - |
SRO | + + + - + + + - - |
SNW | + + + + + + + + - |
SNRW | + + + + + + + + - |
X | + + + + + + + + + |
SU -> X | + + + + + + + + + |
SNW -> X | + + + + + + + + + |
SNRW -> X | + + + + + + + + + |
Here: "+" -- means that request can be satisfied
"-" -- means that request can't be satisfied and should wait
"0" -- means impossible situation which will trigger assert
@note In cases then current context already has "stronger" type
of lock on the object it will be automatically granted
thanks to usage of the MDL_context::find_ticket() method.
@note IX locks are excluded since they are not used for per-object
metadata locks.
*/
const MDL_lock::bitmap_t
MDL_lock::MDL_object_lock::m_granted_incompatible[MDL_TYPE_END]=
{
0,
MDL_BIT(MDL_EXCLUSIVE),
MDL_BIT(MDL_EXCLUSIVE),
MDL_BIT(MDL_EXCLUSIVE) | MDL_BIT(MDL_SHARED_NO_READ_WRITE),
MDL_BIT(MDL_EXCLUSIVE) | MDL_BIT(MDL_SHARED_NO_READ_WRITE) |
MDL_BIT(MDL_SHARED_NO_WRITE) | MDL_BIT(MDL_SHARED_READ_ONLY),
MDL_BIT(MDL_EXCLUSIVE) | MDL_BIT(MDL_SHARED_NO_READ_WRITE) |
MDL_BIT(MDL_SHARED_NO_WRITE) | MDL_BIT(MDL_SHARED_UPGRADABLE),
MDL_BIT(MDL_EXCLUSIVE) | MDL_BIT(MDL_SHARED_NO_READ_WRITE) |
MDL_BIT(MDL_SHARED_WRITE),
MDL_BIT(MDL_EXCLUSIVE) | MDL_BIT(MDL_SHARED_NO_READ_WRITE) |
MDL_BIT(MDL_SHARED_NO_WRITE) | MDL_BIT(MDL_SHARED_UPGRADABLE) |
MDL_BIT(MDL_SHARED_WRITE),
MDL_BIT(MDL_EXCLUSIVE) | MDL_BIT(MDL_SHARED_NO_READ_WRITE) |
MDL_BIT(MDL_SHARED_NO_WRITE) | MDL_BIT(MDL_SHARED_READ_ONLY) |
MDL_BIT(MDL_SHARED_UPGRADABLE) | MDL_BIT(MDL_SHARED_WRITE) |
MDL_BIT(MDL_SHARED_READ),
MDL_BIT(MDL_EXCLUSIVE) | MDL_BIT(MDL_SHARED_NO_READ_WRITE) |
MDL_BIT(MDL_SHARED_NO_WRITE) | MDL_BIT(MDL_SHARED_READ_ONLY) |
MDL_BIT(MDL_SHARED_UPGRADABLE) | MDL_BIT(MDL_SHARED_WRITE) |
MDL_BIT(MDL_SHARED_READ) | MDL_BIT(MDL_SHARED_HIGH_PRIO) |
MDL_BIT(MDL_SHARED)
};
const MDL_lock::bitmap_t
MDL_lock::MDL_object_lock::m_waiting_incompatible[MDL_TYPE_END]=
{
0,
MDL_BIT(MDL_EXCLUSIVE),
0,
MDL_BIT(MDL_EXCLUSIVE) | MDL_BIT(MDL_SHARED_NO_READ_WRITE),
MDL_BIT(MDL_EXCLUSIVE) | MDL_BIT(MDL_SHARED_NO_READ_WRITE) |
MDL_BIT(MDL_SHARED_NO_WRITE),
MDL_BIT(MDL_EXCLUSIVE),
MDL_BIT(MDL_EXCLUSIVE) | MDL_BIT(MDL_SHARED_NO_READ_WRITE) |
MDL_BIT(MDL_SHARED_WRITE),
MDL_BIT(MDL_EXCLUSIVE),
MDL_BIT(MDL_EXCLUSIVE),
0
};
/**
Compatibility (or rather "incompatibility") matrices for backup metadata
lock. Arrays of bitmaps which elements specify which granted/waiting locks
are incompatible with type of lock being requested.
The first array specifies if particular type of request can be satisfied
if there is granted backup lock of certain type.
Request | Type of active backup lock |
type | S0 S1 S2 S3 S4 F1 F2 D TD SD DD BL AC C |
----------+---------------------------------------------------------+
S0 | - - - - - + + + + + + + + + |
S1 | - + + + + + + + + + + + + + |
S2 | - + + + + + + - + + + + + + |
S3 | - + + + + + + - + + - + + + |
S4 | - + + + + + + - + - - + + - |
FTWRL1 | + + + + + + + - - - - + - + |
FTWRL2 | + + + + + + + - - - - + - - |
D | + - - - - - - + + + + + + + |
TD | + + + + + - - + + + + + + + |
SD | + + + + - - - + + + + + + + |
DDL | + + + - - - - + + + + - + + |
BLOCK_DDL | - + + + + + + + + + - + + + |
ALTER_COP | + + + + + - - + + + + + + + |
COMMIT | + + + + - + - + + + + + + + |
The second array specifies if particular type of request can be satisfied
if there is already waiting request for the backup lock of certain type.
I.e. it specifies what is the priority of different lock types.
Request | Pending backup lock |
type | S0 S1 S2 S3 S4 F1 F2 D TD SD DD BL AC C |
----------+---------------------------------------------------------+
S0 | + - - - - + + + + + + + + + |
S1 | + + + + + + + + + + + + + + |
S2 | + + + + + + + + + + + + + + |
S3 | + + + + + + + + + + + + + + |
S4 | + + + + + + + + + + + + + + |
FTWRL1 | + + + + + + + + + + + + + + |
FTWRL2 | + + + + + + + + + + + + + + |
D | + - - - - - - + + + + + + + |
TD | + + + + + - - + + + + + + + |
SD | + + + + - - - + + + + + + + |
DDL | + + + - - - - + + + + - + + |
BLOCK_DDL | + + + + + + + + + + + + + + |
ALTER_COP | + + + + + - - + + + + + + + |
COMMIT | + + + + - + - + + + + + + + |
Here: "+" -- means that request can be satisfied
"-" -- means that request can't be satisfied and should wait
*/
/*
NOTE: If you add a new MDL_BACKUP_XXX level lock, you have to also add it
to MDL_BACKUP_START in the two arrays below!
*/
const MDL_lock::bitmap_t
MDL_lock::MDL_backup_lock::m_granted_incompatible[MDL_BACKUP_END]=
{
/* MDL_BACKUP_START */
MDL_BIT(MDL_BACKUP_START) | MDL_BIT(MDL_BACKUP_FLUSH) | MDL_BIT(MDL_BACKUP_WAIT_FLUSH) | MDL_BIT(MDL_BACKUP_WAIT_DDL) | MDL_BIT(MDL_BACKUP_WAIT_COMMIT) | MDL_BIT(MDL_BACKUP_BLOCK_DDL),
MDL_BIT(MDL_BACKUP_START),
MDL_BIT(MDL_BACKUP_START) | MDL_BIT(MDL_BACKUP_DML),
MDL_BIT(MDL_BACKUP_START) | MDL_BIT(MDL_BACKUP_DML) | MDL_BIT(MDL_BACKUP_DDL),
MDL_BIT(MDL_BACKUP_START) | MDL_BIT(MDL_BACKUP_DML) | MDL_BIT(MDL_BACKUP_SYS_DML) | MDL_BIT(MDL_BACKUP_DDL) | MDL_BIT(MDL_BACKUP_COMMIT),
/* MDL_BACKUP_FTWRL1 */
MDL_BIT(MDL_BACKUP_DML) | MDL_BIT(MDL_BACKUP_TRANS_DML) | MDL_BIT(MDL_BACKUP_SYS_DML) | MDL_BIT(MDL_BACKUP_DDL) | MDL_BIT(MDL_BACKUP_ALTER_COPY),
MDL_BIT(MDL_BACKUP_DML) | MDL_BIT(MDL_BACKUP_TRANS_DML) | MDL_BIT(MDL_BACKUP_SYS_DML) | MDL_BIT(MDL_BACKUP_DDL) | MDL_BIT(MDL_BACKUP_ALTER_COPY) | MDL_BIT(MDL_BACKUP_COMMIT),
/* MDL_BACKUP_DML */
MDL_BIT(MDL_BACKUP_FLUSH) | MDL_BIT(MDL_BACKUP_WAIT_FLUSH) | MDL_BIT(MDL_BACKUP_WAIT_DDL) | MDL_BIT(MDL_BACKUP_WAIT_COMMIT) | MDL_BIT(MDL_BACKUP_FTWRL1) | MDL_BIT(MDL_BACKUP_FTWRL2),
MDL_BIT(MDL_BACKUP_FTWRL1) | MDL_BIT(MDL_BACKUP_FTWRL2),
MDL_BIT(MDL_BACKUP_WAIT_COMMIT) | MDL_BIT(MDL_BACKUP_FTWRL1) | MDL_BIT(MDL_BACKUP_FTWRL2),
/* MDL_BACKUP_DDL */
MDL_BIT(MDL_BACKUP_WAIT_DDL) | MDL_BIT(MDL_BACKUP_WAIT_COMMIT) | MDL_BIT(MDL_BACKUP_FTWRL1) | MDL_BIT(MDL_BACKUP_FTWRL2) | MDL_BIT(MDL_BACKUP_BLOCK_DDL),
/* MDL_BACKUP_BLOCK_DDL */
MDL_BIT(MDL_BACKUP_START) | MDL_BIT(MDL_BACKUP_FLUSH) | MDL_BIT(MDL_BACKUP_WAIT_FLUSH) | MDL_BIT(MDL_BACKUP_WAIT_DDL) | MDL_BIT(MDL_BACKUP_WAIT_COMMIT) | MDL_BIT(MDL_BACKUP_BLOCK_DDL) | MDL_BIT(MDL_BACKUP_DDL),
MDL_BIT(MDL_BACKUP_FTWRL1) | MDL_BIT(MDL_BACKUP_FTWRL2),
/* MDL_BACKUP_COMMIT */
MDL_BIT(MDL_BACKUP_WAIT_COMMIT) | MDL_BIT(MDL_BACKUP_FTWRL2)
};
const MDL_lock::bitmap_t
MDL_lock::MDL_backup_lock::m_waiting_incompatible[MDL_BACKUP_END]=
{
/* MDL_BACKUP_START */
MDL_BIT(MDL_BACKUP_FLUSH) | MDL_BIT(MDL_BACKUP_WAIT_FLUSH) | MDL_BIT(MDL_BACKUP_WAIT_DDL) | MDL_BIT(MDL_BACKUP_WAIT_COMMIT) | MDL_BIT(MDL_BACKUP_BLOCK_DDL),
0,
0,
0,
0,
/* MDL_BACKUP_FTWRL1 */
0,
0,
/* MDL_BACKUP_DML */
MDL_BIT(MDL_BACKUP_FLUSH) | MDL_BIT(MDL_BACKUP_WAIT_FLUSH) | MDL_BIT(MDL_BACKUP_WAIT_DDL) | MDL_BIT(MDL_BACKUP_WAIT_COMMIT) | MDL_BIT(MDL_BACKUP_FTWRL1) | MDL_BIT(MDL_BACKUP_FTWRL2),
MDL_BIT(MDL_BACKUP_FTWRL1) | MDL_BIT(MDL_BACKUP_FTWRL2),
MDL_BIT(MDL_BACKUP_WAIT_COMMIT) | MDL_BIT(MDL_BACKUP_FTWRL1) | MDL_BIT(MDL_BACKUP_FTWRL2),
/* MDL_BACKUP_DDL */
MDL_BIT(MDL_BACKUP_WAIT_DDL) | MDL_BIT(MDL_BACKUP_WAIT_COMMIT) | MDL_BIT(MDL_BACKUP_FTWRL1) | MDL_BIT(MDL_BACKUP_FTWRL2) | MDL_BIT(MDL_BACKUP_BLOCK_DDL),
/* MDL_BACKUP_BLOCK_DDL */
MDL_BIT(MDL_BACKUP_START),
MDL_BIT(MDL_BACKUP_FTWRL1) | MDL_BIT(MDL_BACKUP_FTWRL2),
/* MDL_BACKUP_COMMIT */
MDL_BIT(MDL_BACKUP_WAIT_COMMIT) | MDL_BIT(MDL_BACKUP_FTWRL2)
};
/**
Check if request for the metadata lock can be satisfied given its
current state.
New lock request can be satisfied iff:
- There are no incompatible types of satisfied requests
in other contexts
- There are no waiting requests which have higher priority
than this request when priority was not ignored.
@param type_arg The requested lock type.
@param requestor_ctx The MDL context of the requestor.
@param ignore_lock_priority Ignore lock priority.
@retval TRUE Lock request can be satisfied
@retval FALSE There is some conflicting lock.
@note In cases then current context already has "stronger" type
of lock on the object it will be automatically granted
thanks to usage of the MDL_context::find_ticket() method.
*/
bool
MDL_lock::can_grant_lock(enum_mdl_type type_arg,
MDL_context *requestor_ctx,
bool ignore_lock_priority) const
{
bitmap_t waiting_incompat_map= incompatible_waiting_types_bitmap()[type_arg];
bitmap_t granted_incompat_map= incompatible_granted_types_bitmap()[type_arg];
#ifdef WITH_WSREP
/*
Approve lock request in BACKUP namespace for BF threads.
*/
if (!wsrep_check_mode(WSREP_MODE_BF_MARIABACKUP) &&
(wsrep_thd_is_toi(requestor_ctx->get_thd()) ||
wsrep_thd_is_applying(requestor_ctx->get_thd())) &&
key.mdl_namespace() == MDL_key::BACKUP)
{
bool waiting_incompatible= m_waiting.bitmap() & waiting_incompat_map;
bool granted_incompatible= m_granted.bitmap() & granted_incompat_map;
if (waiting_incompatible || granted_incompatible)
{
WSREP_DEBUG("global lock granted for BF%s: %lu %s",
waiting_incompatible ? " (waiting queue)" : "",
thd_get_thread_id(requestor_ctx->get_thd()),
wsrep_thd_query(requestor_ctx->get_thd()));
}
return true;
}
#endif /* WITH_WSREP */
if (!ignore_lock_priority && (m_waiting.bitmap() & waiting_incompat_map))
return false;
if (m_granted.bitmap() & granted_incompat_map)
{
bool can_grant= true;
/* Check that the incompatible lock belongs to some other context. */
for (const auto &ticket : m_granted)
{
if (ticket.get_ctx() != requestor_ctx &&
ticket.is_incompatible_when_granted(type_arg))
{
can_grant= false;
#ifdef WITH_WSREP
/*
non WSREP threads must report conflict immediately
note: RSU processing wsrep threads, have wsrep_on==OFF
*/
if (WSREP(requestor_ctx->get_thd()) ||
requestor_ctx->get_thd()->wsrep_cs().mode() ==
wsrep::client_state::m_rsu)
{
wsrep_handle_mdl_conflict(requestor_ctx, &ticket, &key);
if (wsrep_log_conflicts)
{
auto key= ticket.get_key();
WSREP_INFO("MDL conflict db=%s table=%s ticket=%d solved by abort",
key->db_name(), key->name(), ticket.get_type());
}
continue;
}
#endif /* WITH_WSREP */
break;
}
}
return can_grant;
}
return true;
}
/**
Removes ticket from waiting or pending queue and awakes waiters.
Once ticket is removed from the list, this thread doesn't hold
references to this lock and it can be destroyed concurrently. It
means once m_rwlock is released, "this" cannot be referenced anymore.
Non-fast lane locks close fast lanes whenever they're registered in
MDL_lock. Whenever such locks are being deregistered, fast lanes must
be reopened. Once all closers are gone, that is number of close calls
equals to number of open calls, fast lanes become available again.
*/
void MDL_lock::remove_ticket(LF_PINS *pins, Ticket_list MDL_lock::*list,
MDL_ticket *ticket)
{
DBUG_ASSERT(!ticket->m_fast_lane.load(std::memory_order_relaxed));
mysql_prlock_wrlock(&m_rwlock);
(this->*list).remove_ticket(ticket);
if (is_empty())
{
/* Never destroy pre-allocated MDL_lock object in BACKUP namespace. */
if (key.mdl_namespace() != MDL_key::BACKUP)
{
m_strategy= 0;
mysql_prlock_unlock(&m_rwlock);
mdl_locks.remove(pins, &key);
return;
}
}
else
{
/*
There can be some contexts waiting to acquire a lock
which now might be able to do it. Grant the lock to
them and wake them up!
We always try to reschedule locks, since there is no easy way
(i.e. by looking at the bitmaps) to find out whether it is
required or not.
In a general case, even when the queue's bitmap is not changed
after removal of the ticket, there is a chance that some request
can be satisfied (due to the fact that a granted request
reflected in the bitmap might belong to the same context as a
pending request).
*/
reschedule_waiters();
}
m_fast_road.reopen(ticket->get_type());
mysql_prlock_unlock(&m_rwlock);
}
MDL_wait_for_graph_visitor::~MDL_wait_for_graph_visitor()
= default;
MDL_wait_for_subgraph::~MDL_wait_for_subgraph()
= default;
/**
Check if ticket represents metadata lock of "stronger" or equal type
than specified one. I.e. if metadata lock represented by ticket won't
allow any of locks which are not allowed by specified type of lock.
@return TRUE if ticket has stronger or equal type
FALSE otherwise.
*/
bool MDL_ticket::has_stronger_or_equal_type(enum_mdl_type type) const
{
const auto *granted_incompat_map= m_lock->incompatible_granted_types_bitmap();
return ! (granted_incompat_map[type] & ~(granted_incompat_map[m_type]));
}
bool MDL_ticket::is_incompatible_when_granted(enum_mdl_type type) const
{
return (MDL_BIT(m_type) &
m_lock->incompatible_granted_types_bitmap()[type]);
}
bool MDL_ticket::is_incompatible_when_waiting(enum_mdl_type type) const
{
return (MDL_BIT(m_type) &
m_lock->incompatible_waiting_types_bitmap()[type]);
}
static const LEX_STRING
*get_mdl_lock_name(MDL_key::enum_mdl_namespace mdl_namespace,
enum_mdl_type type)
{
return mdl_namespace == MDL_key::BACKUP ?
&backup_lock_types[type] :
&lock_types[type];
}
const LEX_STRING *MDL_ticket::get_type_name() const
{
return get_mdl_lock_name(get_key()->mdl_namespace(), m_type);
}
const LEX_STRING *MDL_ticket::get_type_name(enum_mdl_type type) const
{
return get_mdl_lock_name(get_key()->mdl_namespace(), type);
}
/**
Check whether the context already holds a compatible lock ticket
on an object.
Start searching from list of locks for the same duration as lock
being requested. If not look at lists for other durations.
@param mdl_request Lock request object for lock to be acquired
@param[out] result_duration Duration of lock which was found.
@note Tickets which correspond to lock types "stronger" than one
being requested are also considered compatible.
@return A pointer to the lock ticket for the object or NULL otherwise.
*/
MDL_ticket *
MDL_context::find_ticket(MDL_request *mdl_request,
enum_mdl_duration *result_duration)
{
MDL_ticket *ticket;
int i;
for (i= 0; i < MDL_DURATION_END; i++)
{
enum_mdl_duration duration= (enum_mdl_duration)((mdl_request->duration+i) %
MDL_DURATION_END);
Ticket_iterator it(m_tickets[duration]);
while ((ticket= it++))
{
if (mdl_request->key.is_equal(ticket->get_key()) &&
ticket->has_stronger_or_equal_type(mdl_request->type))
{
DBUG_PRINT("info", ("Adding mdl lock %s to %s",
get_mdl_lock_name(mdl_request->key.mdl_namespace(),
mdl_request->type)->str,
ticket->get_type_name()->str));
*result_duration= duration;
return ticket;
}
}
}
return NULL;
}
/**
Try to acquire one lock.
Unlike exclusive locks, shared locks are acquired one by
one. This is interface is chosen to simplify introduction of
the new locking API to the system. MDL_context::try_acquire_lock()
is currently used from open_table(), and there we have only one
table to work with.
This function may also be used to try to acquire an exclusive
lock on a destination table, by ALTER TABLE ... RENAME.
Returns immediately without any side effect if encounters a lock
conflict. Otherwise takes the lock.
FIXME: Compared to lock_table_name_if_not_cached() (from 5.1)
it gives slightly more false negatives.
@param mdl_request [in/out] Lock request object for lock to be acquired
@retval FALSE Success. The lock may have not been acquired.
Check the ticket, if it's NULL, a conflicting lock
exists.
@retval TRUE Out of resources, an error has been reported.
*/
bool
MDL_context::try_acquire_lock(MDL_request *mdl_request)
{
return try_acquire_lock_impl(mdl_request, nullptr);
}
/**
Auxiliary method for acquiring lock without waiting.
@param mdl_request [in/out] Lock request object for lock to be acquired
@param out_ticket [out] Ticket for the request in case when lock
has not been acquired.
@retval FALSE Success. The lock may have not been acquired.
Check MDL_request::ticket, if it's NULL, a conflicting
lock exists. In this case "out_ticket" out parameter
points to ticket which was constructed for the request.
MDL_ticket::m_lock points to the corresponding MDL_lock
object and MDL_lock::m_rwlock write-locked.
@retval TRUE Out of resources, an error has been reported.
*/
bool
MDL_context::try_acquire_lock_impl(MDL_request *mdl_request,
MDL_ticket **out_ticket)
{
MDL_ticket *ticket;
enum_mdl_duration found_duration;
/* Don't take chances in production. */
DBUG_ASSERT(mdl_request->ticket == NULL);
mdl_request->ticket= NULL;
/*
Check whether the context already holds a shared lock on the object,
and if so, grant the request.
*/
if ((ticket= find_ticket(mdl_request, &found_duration)))
{
DBUG_ASSERT(ticket->m_lock);
DBUG_ASSERT(ticket->has_stronger_or_equal_type(mdl_request->type));
/*
If the request is for a transactional lock, and we found
a transactional lock, just reuse the found ticket.
It's possible that we found a transactional lock,
but the request is for a HANDLER lock. In that case HANDLER
code will clone the ticket (see below why it's needed).
If the request is for a transactional lock, and we found
a HANDLER lock, create a copy, to make sure that when user
does HANDLER CLOSE, the transactional lock is not released.
If the request is for a handler lock, and we found a
HANDLER lock, also do the clone. HANDLER CLOSE for one alias
should not release the lock on the table HANDLER opened through
a different alias.
*/
mdl_request->ticket= ticket;
if ((found_duration != mdl_request->duration ||
mdl_request->duration == MDL_EXPLICIT) &&
clone_ticket(mdl_request))
{
/* Clone failed. */
mdl_request->ticket= NULL;
return TRUE;
}
return FALSE;
}
if (fix_pins())
return TRUE;
if (!(ticket= new (std::nothrow) MDL_ticket(this, mdl_request)))
return TRUE;
if (metadata_lock_info_plugin_loaded)
ticket->m_time= microsecond_interval_timer();
switch (mdl_locks.try_acquire_lock(m_pins, &mdl_request->key, ticket,
out_ticket != nullptr)) {
case TAL_ACQUIRED:
m_tickets[mdl_request->duration].push_front(ticket);
mdl_request->ticket= ticket;
mysql_mdl_set_status(ticket->m_psi, MDL_ticket::GRANTED);
break;
case TAL_WAIT:
DBUG_ASSERT(out_ticket);
*out_ticket= ticket;
break;
case TAL_NOWAIT:
DBUG_PRINT("mdl", ("Nowait: <ticket->m_lock unavailable>"));
delete ticket;
break;
default:
delete ticket;
return TRUE;
}
return FALSE;
}
/**
Create a copy of a granted ticket.
This is used to make sure that HANDLER ticket
is never shared with a ticket that belongs to
a transaction, so that when we HANDLER CLOSE,
we don't release a transactional ticket, and
vice versa -- when we COMMIT, we don't mistakenly
release a ticket for an open HANDLER.
@retval TRUE Out of memory.
@retval FALSE Success.
*/
bool
MDL_context::clone_ticket(MDL_request *mdl_request)
{
MDL_ticket *ticket;
/*
Since in theory we can clone ticket belonging to a different context
we need to prepare target context for possible attempts to release
lock and thus possible removal of MDL_lock from MDL_map container.
So we allocate pins to be able to work with this container if they
are not allocated already.
*/
if (fix_pins())
return TRUE;
/*
By submitting mdl_request->type to MDL_ticket constructor
we effectively downgrade the cloned lock to the level of
the request.
*/
if (!(ticket= new (std::nothrow) MDL_ticket(this, mdl_request)))
return TRUE;
/* clone() is not supposed to be used to get a stronger lock. */
DBUG_ASSERT(mdl_request->ticket->has_stronger_or_equal_type(ticket->m_type));
ticket->m_lock= mdl_request->ticket->m_lock;
ticket->m_time= mdl_request->ticket->m_time;
mdl_request->ticket= ticket;
ticket->m_lock->add_cloned_ticket(ticket);
m_tickets[mdl_request->duration].push_front(ticket);
mysql_mdl_set_status(ticket->m_psi, MDL_ticket::GRANTED);
return FALSE;
}
/**
Check if there is any conflicting lock that could cause this thread
to wait for another thread which is not ready to commit.
This is always an error, as the upper level of parallel replication
should not allow a scheduling of a conflicting DDL until all earlier
transactions have been committed.
This function is only called for a slave using parallel replication
and trying to get an exclusive lock for the table.
*/
#ifndef DBUG_OFF
bool MDL_lock::check_if_conflicting_replication_locks(MDL_context *ctx)
{
rpl_group_info *rgi_slave= ctx->get_thd()->rgi_slave;
if (!rgi_slave->gtid_sub_id)
return 0;
for (const auto &conflicting_ticket : m_granted)
{
if (conflicting_ticket.get_ctx() != ctx)
{
MDL_context *conflicting_ctx= conflicting_ticket.get_ctx();
rpl_group_info *conflicting_rgi_slave;
conflicting_rgi_slave= conflicting_ctx->get_thd()->rgi_slave;
/*
If the conflicting thread is another parallel replication
thread for the same master and it's not in commit or post-commit stages,
then the current transaction has started too early and something is
seriously wrong.
*/
if (conflicting_rgi_slave &&
conflicting_rgi_slave->gtid_sub_id &&
conflicting_rgi_slave->rli == rgi_slave->rli &&
conflicting_rgi_slave->current_gtid.domain_id ==
rgi_slave->current_gtid.domain_id &&
!((conflicting_rgi_slave->did_mark_start_commit ||
conflicting_rgi_slave->worker_error) ||
conflicting_rgi_slave->finish_event_group_called))
return 1; // Fatal error
}
}
return 0;
}
#endif
/**
Acquire one lock with waiting for conflicting locks to go away if needed.
@param mdl_request [in/out] Lock request object for lock to be acquired
@param lock_wait_timeout [in] Seconds to wait before timeout.
@retval FALSE Success. MDL_request::ticket points to the ticket
for the lock.
@retval TRUE Failure (Out of resources or waiting is aborted),
*/
bool
MDL_context::acquire_lock(MDL_request *mdl_request, double lock_wait_timeout)
{
MDL_lock *lock;
MDL_ticket *ticket;
MDL_wait::enum_wait_status wait_status;
DBUG_ENTER("MDL_context::acquire_lock");
DBUG_ASSERT(m_wait.get_status() == MDL_wait::EMPTY);
#ifdef DBUG_TRACE
const char *mdl_lock_name= get_mdl_lock_name(
mdl_request->key.mdl_namespace(), mdl_request->type)->str;
#endif
DBUG_PRINT("enter", ("lock_type: %s timeout: %f",
mdl_lock_name,
lock_wait_timeout));
if (try_acquire_lock_impl(mdl_request, lock_wait_timeout ? &ticket : nullptr))
{
DBUG_PRINT("mdl", ("OOM: %s", mdl_lock_name));
DBUG_RETURN(TRUE);
}
if (mdl_request->ticket)
{
/*
We have managed to acquire lock without waiting.
MDL_lock, MDL_context and MDL_request were updated
accordingly, so we can simply return success.
*/
DBUG_PRINT("info", ("Got lock without waiting"));
DBUG_PRINT("mdl", ("Seized: %s", dbug_print_mdl(mdl_request->ticket)));
DBUG_RETURN(FALSE);
}
/*
Our attempt to acquire lock without waiting has failed.
As a result of this attempt we got MDL_ticket with m_lock
member pointing to the corresponding MDL_lock object which
has MDL_lock::m_rwlock write-locked.
*/
if (lock_wait_timeout == 0)
{
my_error(ER_LOCK_WAIT_TIMEOUT, MYF(0));
DBUG_RETURN(TRUE);
}
#ifdef DBUG_TRACE
const char *ticket_msg= dbug_print_mdl(ticket);
#endif
#ifdef WITH_WSREP
if (WSREP(get_thd()))
{
THD* requester= get_thd();
bool requester_toi= wsrep_thd_is_toi(requester) || wsrep_thd_is_applying(requester);
WSREP_DEBUG("::acquire_lock is TOI %d for %s", requester_toi,
wsrep_thd_query(requester));
if (requester_toi)
THD_STAGE_INFO(requester, stage_waiting_ddl);
else
THD_STAGE_INFO(requester, stage_waiting_isolation);
}
#endif /* WITH_WSREP */
lock= ticket->m_lock;
#ifdef HAVE_PSI_INTERFACE
PSI_metadata_locker_state state __attribute__((unused));
PSI_metadata_locker *locker= NULL;
if (ticket->m_psi != NULL)
locker= PSI_CALL_start_metadata_wait(&state, ticket->m_psi, __FILE__, __LINE__);
#endif
DBUG_PRINT("mdl", ("Waiting: %s", ticket_msg));
will_wait_for(ticket);
/* There is a shared or exclusive lock on the object. */
DEBUG_SYNC(get_thd(), "mdl_acquire_lock_wait");
find_deadlock();
struct timespec abs_timeout, abs_shortwait, abs_abort_blocking_timeout;
bool abort_blocking_enabled= false;
double abort_blocking_timeout= slave_abort_blocking_timeout;
if (abort_blocking_timeout < lock_wait_timeout &&
m_owner->get_thd()->rgi_slave)
{
/*
After @@slave_abort_blocking_timeout seconds, kill non-replication
queries that are blocking a replication event (such as an ALTER TABLE)
from proceeding.
*/
set_timespec_nsec(abs_abort_blocking_timeout,
(ulonglong)(abort_blocking_timeout * 1000000000ULL));
abort_blocking_enabled= true;
}
set_timespec_nsec(abs_timeout,
(ulonglong)(lock_wait_timeout * 1000000000ULL));
wait_status= MDL_wait::EMPTY;
for (;;)
{
bool abort_blocking= false;
set_timespec(abs_shortwait, 1);
if (abort_blocking_enabled &&
cmp_timespec(abs_shortwait, abs_abort_blocking_timeout) >= 0)
{
/*
If a slave DDL has waited for --slave-abort-select-timeout, then notify
any blocking SELECT once before continuing to wait until the full
timeout.
*/
abs_shortwait= abs_abort_blocking_timeout;
abort_blocking= true;
abort_blocking_enabled= false;
}
else if (cmp_timespec(abs_shortwait, abs_timeout) > 0)
break;
/* abs_timeout is far away. Wait a short while and notify locks. */
wait_status= m_wait.timed_wait(m_owner, &abs_shortwait, FALSE,
mdl_request->key.get_wait_state_name());
if (wait_status != MDL_wait::EMPTY)
break;
/* Check if the client is gone while we were waiting. */
if (! thd_is_connected(m_owner->get_thd()))
{
/*
* The client is disconnected. Don't wait forever:
* assume it's the same as a wait timeout, this
* ensures all error handling is correct.
*/
wait_status= MDL_wait::TIMEOUT;
break;
}
lock->notify_conflicting_locks_if_needed(ticket, abort_blocking);
}
if (wait_status == MDL_wait::EMPTY)
wait_status= m_wait.timed_wait(m_owner, &abs_timeout, TRUE,
mdl_request->key.get_wait_state_name());
done_waiting_for();
#ifdef HAVE_PSI_INTERFACE
if (locker != NULL)
PSI_CALL_end_metadata_wait(locker, 0);
#endif
if (wait_status != MDL_wait::GRANTED)
{
lock->abort_wait(m_pins, ticket);
m_wait.reset_status();
delete ticket;
switch (wait_status)
{
case MDL_wait::VICTIM:
DBUG_PRINT("mdl", ("Deadlock: %s", ticket_msg));
DBUG_PRINT("mdl_locks", ("Existing locks:%s", mdl_dbug_print_locks()));
my_error(ER_LOCK_DEADLOCK, MYF(0));
break;
case MDL_wait::TIMEOUT:
DBUG_PRINT("mdl", ("Timeout: %s", ticket_msg));
my_error(ER_LOCK_WAIT_TIMEOUT, MYF(0));
break;
case MDL_wait::KILLED:
DBUG_PRINT("mdl", ("Killed: %s", ticket_msg));
get_thd()->send_kill_message();
break;
default:
DBUG_ASSERT(0);
break;
}
DBUG_RETURN(TRUE);
}
/*
We have been granted our request.
State of MDL_lock object is already being appropriately updated by a
concurrent thread (@sa MDL_lock:reschedule_waiters()).
So all we need to do is to update MDL_context and MDL_request objects.
*/
m_wait.reset_status();
m_tickets[mdl_request->duration].push_front(ticket);
mdl_request->ticket= ticket;
mysql_mdl_set_status(ticket->m_psi, MDL_ticket::GRANTED);
DBUG_PRINT("mdl", ("Acquired: %s", ticket_msg));
DBUG_RETURN(FALSE);
}
extern "C" int mdl_request_ptr_cmp(const void* ptr1, const void* ptr2)
{
MDL_request *req1= *(MDL_request**)ptr1;
MDL_request *req2= *(MDL_request**)ptr2;
return req1->key.cmp(&req2->key);
}
/**
Acquire exclusive locks. There must be no granted locks in the
context.
This is a replacement of lock_table_names(). It is used in
RENAME, DROP and other DDL SQL statements.
@param mdl_requests List of requests for locks to be acquired.
@param lock_wait_timeout Seconds to wait before timeout.
@note The list of requests should not contain non-exclusive lock requests.
There should not be any acquired locks in the context.
@note Assumes that one already owns scoped intention exclusive lock.
@retval FALSE Success
@retval TRUE Failure
*/
bool MDL_context::acquire_locks(MDL_request_list *mdl_requests,
double lock_wait_timeout)
{
MDL_request_list::Iterator it(*mdl_requests);
MDL_request **sort_buf, **p_req;
MDL_savepoint mdl_svp= mdl_savepoint();
ssize_t req_count= static_cast<ssize_t>(mdl_requests->elements());
DBUG_ENTER("MDL_context::acquire_locks");
if (req_count == 0)
DBUG_RETURN(FALSE);
/* Sort requests according to MDL_key. */
if (! (sort_buf= (MDL_request **)my_malloc(key_memory_MDL_context_acquire_locks,
req_count * sizeof(MDL_request*),
MYF(MY_WME))))
DBUG_RETURN(TRUE);
for (p_req= sort_buf; p_req < sort_buf + req_count; p_req++)
*p_req= it++;
my_qsort(sort_buf, req_count, sizeof(MDL_request*),
mdl_request_ptr_cmp);
for (p_req= sort_buf; p_req < sort_buf + req_count; p_req++)
{
if (acquire_lock(*p_req, lock_wait_timeout))
goto err;
}
my_free(sort_buf);
DBUG_RETURN(FALSE);
err:
/*
Release locks we have managed to acquire so far.
Use rollback_to_savepoint() since there may be duplicate
requests that got assigned the same ticket.
*/
rollback_to_savepoint(mdl_svp);
/* Reset lock requests back to its initial state. */
for (req_count= p_req - sort_buf, p_req= sort_buf;
p_req < sort_buf + req_count; p_req++)
{
(*p_req)->ticket= NULL;
}
my_free(sort_buf);
DBUG_RETURN(TRUE);
}
/**
Upgrade a shared metadata lock.
Used in ALTER TABLE.
@param mdl_ticket Lock to upgrade.
@param new_type Lock type to upgrade to.
@param lock_wait_timeout Seconds to wait before timeout.
@note In case of failure to upgrade lock (e.g. because upgrader
was killed) leaves lock in its original state (locked in
shared mode).
@note There can be only one upgrader for a lock or we will have deadlock.
This invariant is ensured by the fact that upgradeable locks SU, SNW
and SNRW are not compatible with each other and themselves.
If mdl_ticket was granted via fast lanes it can only be upgraded to fast
lane lock type. Try fast upgrade in this case, no need to acquire new
ticket and do conventional upgrade as there're no waiters possible.
If fast upgrade fails, do conventional upgrade.
@retval FALSE Success
@retval TRUE Failure (thread was killed)
*/
bool
MDL_context::upgrade_shared_lock(MDL_ticket *mdl_ticket,
enum_mdl_type new_type,
double lock_wait_timeout)
{
MDL_request mdl_xlock_request;
MDL_savepoint mdl_svp= mdl_savepoint();
bool is_new_ticket;
DBUG_ENTER("MDL_context::upgrade_shared_lock");
DBUG_PRINT("enter",("old_type: %s new_type: %s lock_wait_timeout: %f",
mdl_ticket->get_type_name()->str,
mdl_ticket->get_type_name(new_type)->str,
lock_wait_timeout));
DEBUG_SYNC(get_thd(), "mdl_upgrade_lock");
/*
Do nothing if already upgraded. Used when we FLUSH TABLE under
LOCK TABLES and a table is listed twice in LOCK TABLES list.
In BACKUP namespace upgrade must always happen. Even though
MDL_BACKUP_START is not stronger than MDL_BACKUP_FLUSH from
has_stronger_or_equal_type(), the latter effectively blocks
new MDL_BACKUP_DML while the former doesn't.
*/
if (mdl_ticket->has_stronger_or_equal_type(new_type) &&
mdl_ticket->get_key()->mdl_namespace() != MDL_key::BACKUP)
DBUG_RETURN(FALSE);
if (mdl_ticket->get_lock()->try_fast_upgrade(mdl_ticket, new_type))
DBUG_RETURN(false);
MDL_REQUEST_INIT_BY_KEY(&mdl_xlock_request, mdl_ticket->get_key(),
new_type, MDL_TRANSACTION);
if (acquire_lock(&mdl_xlock_request, lock_wait_timeout))
DBUG_RETURN(TRUE);
is_new_ticket= ! has_lock(mdl_svp, mdl_xlock_request.ticket);
/* Merge the acquired and the original lock. */
mdl_ticket->m_lock->upgrade(mdl_ticket, new_type,
is_new_ticket ? mdl_xlock_request.ticket : nullptr);
if (is_new_ticket)
{
m_tickets[MDL_TRANSACTION].remove(mdl_xlock_request.ticket);
delete mdl_xlock_request.ticket;
}
DBUG_RETURN(FALSE);
}
/**
A fragment of recursive traversal of the wait-for graph
in search for deadlocks. Direct the deadlock visitor to all
contexts that own the lock the current node in the wait-for
graph is waiting for.
As long as the initial node is remembered in the visitor,
a deadlock is found when the same node is seen twice.
*/
bool MDL_lock::visit_subgraph(MDL_ticket *waiting_ticket,
MDL_wait_for_graph_visitor *gvisitor)
{
MDL_context *src_ctx= waiting_ticket->get_ctx();
bool result= TRUE;
mysql_prlock_rdlock(&m_rwlock);
/*
MDL_lock's waiting and granted queues and MDL_context::m_waiting_for
member are updated by different threads when the lock is granted
(see MDL_context::acquire_lock() and MDL_lock::reschedule_waiters()).
As a result, here we may encounter a situation when MDL_lock data
already reflects the fact that the lock was granted but
m_waiting_for member has not been updated yet.
For example, imagine that:
thread1: Owns SNW lock on table t1.
thread2: Attempts to acquire SW lock on t1,
but sees an active SNW lock.
Thus adds the ticket to the waiting queue and
sets m_waiting_for to point to the ticket.
thread1: Releases SNW lock, updates MDL_lock object to
grant SW lock to thread2 (moves the ticket for
SW from waiting to the active queue).
Attempts to acquire a new SNW lock on t1,
sees an active SW lock (since it is present in the
active queue), adds ticket for SNW lock to the waiting
queue, sets m_waiting_for to point to this ticket.
At this point deadlock detection algorithm run by thread1 will see that:
- Thread1 waits for SNW lock on t1 (since m_waiting_for is set).
- SNW lock is not granted, because it conflicts with active SW lock
owned by thread 2 (since ticket for SW is present in granted queue).
- Thread2 waits for SW lock (since its m_waiting_for has not been
updated yet!).
- SW lock is not granted because there is pending SNW lock from thread1.
Therefore deadlock should exist [sic!].
To avoid detection of such false deadlocks we need to check the "actual"
status of the ticket being waited for, before analyzing its blockers.
We do this by checking the wait status of the context which is waiting
for it. To avoid races this has to be done under protection of
MDL_lock::m_rwlock lock.
*/
if (src_ctx->m_wait.get_status() != MDL_wait::EMPTY)
{
result= FALSE;
goto end;
}
/*
To avoid visiting nodes which were already marked as victims of
deadlock detection (or whose requests were already satisfied) we
enter the node only after peeking at its wait status.
This is necessary to avoid active waiting in a situation
when previous searches for a deadlock already selected the
node we're about to enter as a victim (see the comment
in MDL_context::find_deadlock() for explanation why several searches
can be performed for the same wait).
There is no guarantee that the node isn't chosen a victim while we
are visiting it but this is OK: in the worst case we might do some
extra work and one more context might be chosen as a victim.
*/
if (gvisitor->enter_node(src_ctx))
goto end;
/*
We do a breadth-first search first -- that is, inspect all
edges of the current node, and only then follow up to the next
node. In workloads that involve wait-for graph loops this
has proven to be a more efficient strategy [citation missing].
*/
for (const auto& ticket : m_granted)
{
/* Filter out edges that point to the same node. */
if (ticket.get_ctx() != src_ctx &&
ticket.is_incompatible_when_granted(waiting_ticket->get_type()) &&
gvisitor->inspect_edge(ticket.get_ctx()))
{
goto end_leave_node;
}
}
for (const auto &ticket : m_waiting)
{
/* Filter out edges that point to the same node. */
if (ticket.get_ctx() != src_ctx &&
ticket.is_incompatible_when_waiting(waiting_ticket->get_type()) &&
gvisitor->inspect_edge(ticket.get_ctx()))
{
goto end_leave_node;
}
}
/* Recurse and inspect all adjacent nodes. */
for (const auto &ticket : m_granted)
{
if (ticket.get_ctx() != src_ctx &&
ticket.is_incompatible_when_granted(waiting_ticket->get_type()) &&
ticket.get_ctx()->visit_subgraph(gvisitor))
{
goto end_leave_node;
}
}
for (const auto &ticket : m_waiting)
{
if (ticket.get_ctx() != src_ctx &&
ticket.is_incompatible_when_waiting(waiting_ticket->get_type()) &&
ticket.get_ctx()->visit_subgraph(gvisitor))
{
goto end_leave_node;
}
}
result= FALSE;
end_leave_node:
gvisitor->leave_node(src_ctx);
end:
mysql_prlock_unlock(&m_rwlock);
return result;
}
/**
Traverse a portion of wait-for graph which is reachable
through the edge represented by this ticket and search
for deadlocks.
@retval TRUE A deadlock is found. A pointer to deadlock
victim is saved in the visitor.
@retval FALSE
*/
bool MDL_ticket::accept_visitor(MDL_wait_for_graph_visitor *gvisitor)
{
return m_lock->visit_subgraph(this, gvisitor);
}
/**
A fragment of recursive traversal of the wait-for graph of
MDL contexts in the server in search for deadlocks.
Assume this MDL context is a node in the wait-for graph,
and direct the visitor to all adjacent nodes. As long
as the starting node is remembered in the visitor, a
deadlock is found when the same node is visited twice.
One MDL context is connected to another in the wait-for
graph if it waits on a resource that is held by the other
context.
@retval TRUE A deadlock is found. A pointer to deadlock
victim is saved in the visitor.
@retval FALSE
*/
bool MDL_context::visit_subgraph(MDL_wait_for_graph_visitor *gvisitor)
{
bool result= FALSE;
mysql_prlock_rdlock(&m_LOCK_waiting_for);
if (m_waiting_for)
result= m_waiting_for->accept_visitor(gvisitor);
mysql_prlock_unlock(&m_LOCK_waiting_for);
return result;
}
/**
Try to find a deadlock. This function produces no errors.
@note If during deadlock resolution context which performs deadlock
detection is chosen as a victim it will be informed about the
fact by setting VICTIM status to its wait slot.
*/
void MDL_context::find_deadlock()
{
while (1)
{
/*
The fact that we use fresh instance of gvisitor for each
search performed by find_deadlock() below is important,
the code responsible for victim selection relies on this.
*/
Deadlock_detection_visitor dvisitor(this);
MDL_context *victim;
if (! visit_subgraph(&dvisitor))
{
/* No deadlocks are found! */
break;
}
victim= dvisitor.get_victim();
/*
Failure to change status of the victim is OK as it means
that the victim has received some other message and is
about to stop its waiting/to break deadlock loop.
Even when the initiator of the deadlock search is
chosen the victim, we need to set the respective wait
result in order to "close" it for any attempt to
schedule the request.
This is needed to avoid a possible race during
cleanup in case when the lock request on which the
context was waiting is concurrently satisfied.
*/
(void) victim->m_wait.set_status(MDL_wait::VICTIM);
victim->inc_deadlock_overweight();
victim->unlock_deadlock_victim();
if (victim == this)
break;
/*
After adding a new edge to the waiting graph we found that it
creates a loop (i.e. there is a deadlock). We decided to destroy
this loop by removing an edge, but not the one that we added.
Since this doesn't guarantee that all loops created by addition
of the new edge are destroyed, we have to repeat the search.
*/
}
}
/**
Release lock.
@param duration Lock duration.
@param ticket Ticket for lock to be released.
*/
void MDL_context::release_lock(enum_mdl_duration duration, MDL_ticket *ticket)
{
MDL_lock *lock= ticket->m_lock;
DBUG_ENTER("MDL_context::release_lock");
DBUG_PRINT("enter", ("db: '%s' name: '%s'",
ticket->get_key()->db_name(),
ticket->get_key()->name()));
DBUG_ASSERT(this == ticket->get_ctx());
DBUG_PRINT("mdl", ("Released: %s", dbug_print_mdl(ticket)));
lock->release(m_pins, ticket);
m_tickets[duration].remove(ticket);
delete ticket;
DBUG_VOID_RETURN;
}
/**
Release lock with explicit duration.
@param ticket Ticket for lock to be released.
*/
void MDL_context::release_lock(MDL_ticket *ticket)
{
DBUG_SLOW_ASSERT(ticket->m_duration == MDL_EXPLICIT);
release_lock(MDL_EXPLICIT, ticket);
}
/**
Release all locks associated with the context. If the sentinel
is not NULL, do not release locks stored in the list after and
including the sentinel.
Statement and transactional locks are added to the beginning of
the corresponding lists, i.e. stored in reverse temporal order.
This allows to employ this function to:
- back off in case of a lock conflict.
- release all locks in the end of a statement or transaction
- rollback to a savepoint.
*/
void MDL_context::release_locks_stored_before(enum_mdl_duration duration,
MDL_ticket *sentinel)
{
MDL_ticket *ticket;
Ticket_iterator it(m_tickets[duration]);
DBUG_ENTER("MDL_context::release_locks_stored_before");
if (m_tickets[duration].is_empty())
DBUG_VOID_RETURN;
while ((ticket= it++) && ticket != sentinel)
{
DBUG_PRINT("info", ("found lock to release ticket=%p", ticket));
release_lock(duration, ticket);
}
DBUG_VOID_RETURN;
}
/**
Release all explicit locks in the context which correspond to the
same name/object as this lock request.
@param ticket One of the locks for the name/object for which all
locks should be released.
*/
void MDL_context::release_all_locks_for_name(MDL_ticket *name)
{
/* Use MDL_ticket::m_lock to identify other locks for the same object. */
MDL_lock *lock= name->m_lock;
/* Remove matching lock tickets from the context. */
MDL_ticket *ticket;
Ticket_iterator it_ticket(m_tickets[MDL_EXPLICIT]);
while ((ticket= it_ticket++))
{
DBUG_ASSERT(ticket->m_lock);
if (ticket->m_lock == lock)
release_lock(MDL_EXPLICIT, ticket);
}
}
/**
Downgrade an EXCLUSIVE or SHARED_NO_WRITE lock to shared metadata lock.
@param type Type of lock to which exclusive lock should be downgraded.
*/
void MDL_ticket::downgrade_lock(enum_mdl_type type)
{
DBUG_ENTER("MDL_ticket::downgrade_lock");
DBUG_PRINT("enter",("old_type: %s new_type: %s",
get_type_name()->str,
get_type_name(type)->str));
/*
Do nothing if already downgraded. Used when we FLUSH TABLE under
LOCK TABLES and a table is listed twice in LOCK TABLES list.
Note that this code might even try to "downgrade" a weak lock
(e.g. SW) to a stronger one (e.g SNRW). So we can't even assert
here that target lock is weaker than existing lock.
*/
if (m_type == type || !has_stronger_or_equal_type(type))
{
DBUG_PRINT("info", ("Nothing to downgrade"));
DBUG_VOID_RETURN;
}
/* Only allow downgrade in some specific known cases */
DBUG_ASSERT((get_key()->mdl_namespace() != MDL_key::BACKUP &&
(m_type == MDL_EXCLUSIVE ||
m_type == MDL_SHARED_NO_WRITE)) ||
(get_key()->mdl_namespace() == MDL_key::BACKUP &&
(m_type == MDL_BACKUP_DDL ||
m_type == MDL_BACKUP_BLOCK_DDL ||
m_type == MDL_BACKUP_WAIT_FLUSH)));
m_lock->downgrade(this, type);
DBUG_VOID_RETURN;
}
/**
Auxiliary function which allows to check if we have some kind of lock on
a object. Returns TRUE if we have a lock of a given or stronger type.
@param mdl_namespace Id of object namespace
@param db Name of the database
@param name Name of the object
@param mdl_type Lock type. Pass in the weakest type to find
out if there is at least some lock.
@return TRUE if current context contains satisfied lock for the object,
FALSE otherwise.
*/
bool
MDL_context::is_lock_owner(MDL_key::enum_mdl_namespace mdl_namespace,
const char *db, const char *name,
enum_mdl_type mdl_type)
{
MDL_request mdl_request;
enum_mdl_duration not_unused;
/* We don't care about exact duration of lock here. */
MDL_REQUEST_INIT(&mdl_request, mdl_namespace, db, name, mdl_type,
MDL_TRANSACTION);
MDL_ticket *ticket= find_ticket(&mdl_request, &not_unused);
DBUG_ASSERT(ticket == NULL || ticket->m_lock);
return ticket;
}
/**
Return thread id of the owner of the lock or 0 if
there is no owner.
@note: Lock type is not considered at all, the function
simply checks that there is some lock for the given key.
@return thread id of the owner of the lock or 0
*/
unsigned long
MDL_context::get_lock_owner(MDL_key *key)
{
fix_pins();
return mdl_locks.get_lock_owner(m_pins, key);
}
/**
Check if we have any pending locks which conflict with existing shared lock.
@pre The ticket must match an acquired lock.
@return TRUE if there is a conflicting lock request, FALSE otherwise.
*/
bool MDL_ticket::has_pending_conflicting_lock() const
{
return m_lock->has_pending_conflicting_lock(m_type);
}
/** Return a key identifying this lock. */
const MDL_key *MDL_ticket::get_key() const
{
return m_lock->get_key();
}
/**
Releases metadata locks that were acquired after a specific savepoint.
@note Used to release tickets acquired during a savepoint unit.
@note It's safe to iterate and unlock any locks after taken after this
savepoint because other statements that take other special locks
cause a implicit commit (ie LOCK TABLES).
*/
void MDL_context::rollback_to_savepoint(const MDL_savepoint &mdl_savepoint)
{
DBUG_ENTER("MDL_context::rollback_to_savepoint");
/* If savepoint is NULL, it is from the start of the transaction. */
release_locks_stored_before(MDL_STATEMENT, mdl_savepoint.m_stmt_ticket);
release_locks_stored_before(MDL_TRANSACTION, mdl_savepoint.m_trans_ticket);
DBUG_VOID_RETURN;
}
/**
Release locks acquired by normal statements (SELECT, UPDATE,
DELETE, etc) in the course of a transaction. Do not release
HANDLER locks, if there are any.
This method is used at the end of a transaction, in
implementation of COMMIT (implicit or explicit) and ROLLBACK.
*/
void MDL_context::release_transactional_locks(THD *thd)
{
DBUG_ENTER("MDL_context::release_transactional_locks");
/* Fail if there are active transactions */
DBUG_ASSERT(!(thd->server_status &
(SERVER_STATUS_IN_TRANS | SERVER_STATUS_IN_TRANS_READONLY)));
release_locks_stored_before(MDL_STATEMENT, NULL);
release_locks_stored_before(MDL_TRANSACTION, NULL);
DBUG_VOID_RETURN;
}
void MDL_context::release_statement_locks()
{
DBUG_ENTER("MDL_context::release_transactional_locks");
release_locks_stored_before(MDL_STATEMENT, NULL);
DBUG_VOID_RETURN;
}
/**
Does this savepoint have this lock?
@retval TRUE The ticket is older than the savepoint or
is an LT, HA or GLR ticket. Thus it belongs
to the savepoint or has explicit duration.
@retval FALSE The ticket is newer than the savepoint.
and is not an LT, HA or GLR ticket.
*/
bool MDL_context::has_lock(const MDL_savepoint &mdl_savepoint,
MDL_ticket *mdl_ticket)
{
MDL_ticket *ticket;
/* Start from the beginning, most likely mdl_ticket's been just acquired. */
MDL_context::Ticket_iterator s_it(m_tickets[MDL_STATEMENT]);
MDL_context::Ticket_iterator t_it(m_tickets[MDL_TRANSACTION]);
while ((ticket= s_it++) && ticket != mdl_savepoint.m_stmt_ticket)
{
if (ticket == mdl_ticket)
return FALSE;
}
while ((ticket= t_it++) && ticket != mdl_savepoint.m_trans_ticket)
{
if (ticket == mdl_ticket)
return FALSE;
}
return TRUE;
}
/**
Change lock duration for transactional lock.
@param ticket Ticket representing lock.
@param duration Lock duration to be set.
@note This method only supports changing duration of
transactional lock to some other duration.
*/
void MDL_context::set_lock_duration(MDL_ticket *mdl_ticket,
enum_mdl_duration duration)
{
DBUG_SLOW_ASSERT(mdl_ticket->m_duration == MDL_TRANSACTION &&
duration != MDL_TRANSACTION);
m_tickets[MDL_TRANSACTION].remove(mdl_ticket);
m_tickets[duration].push_front(mdl_ticket);
#ifndef DBUG_OFF
mdl_ticket->m_duration= duration;
#endif
}
/**
Set explicit duration for all locks in the context.
*/
void MDL_context::set_explicit_duration_for_all_locks()
{
int i;
MDL_ticket *ticket;
/*
In the most common case when this function is called list
of transactional locks is bigger than list of locks with
explicit duration. So we start by swapping these two lists
and then move elements from new list of transactional
locks and list of statement locks to list of locks with
explicit duration.
*/
m_tickets[MDL_EXPLICIT].swap(m_tickets[MDL_TRANSACTION]);
for (i= 0; i < MDL_EXPLICIT; i++)
{
Ticket_iterator it_ticket(m_tickets[i]);
while ((ticket= it_ticket++))
{
m_tickets[i].remove(ticket);
m_tickets[MDL_EXPLICIT].push_front(ticket);
}
}
#ifndef DBUG_OFF
Ticket_iterator exp_it(m_tickets[MDL_EXPLICIT]);
while ((ticket= exp_it++))
ticket->m_duration= MDL_EXPLICIT;
#endif
}
/**
Set transactional duration for all locks in the context.
*/
void MDL_context::set_transaction_duration_for_all_locks()
{
MDL_ticket *ticket;
/*
In the most common case when this function is called list
of explicit locks is bigger than two other lists (in fact,
list of statement locks is always empty). So we start by
swapping list of explicit and transactional locks and then
move contents of new list of explicit locks to list of
locks with transactional duration.
*/
DBUG_ASSERT(m_tickets[MDL_STATEMENT].is_empty());
m_tickets[MDL_TRANSACTION].swap(m_tickets[MDL_EXPLICIT]);
Ticket_iterator it_ticket(m_tickets[MDL_EXPLICIT]);
while ((ticket= it_ticket++))
{
m_tickets[MDL_EXPLICIT].remove(ticket);
m_tickets[MDL_TRANSACTION].push_front(ticket);
}
#ifndef DBUG_OFF
Ticket_iterator trans_it(m_tickets[MDL_TRANSACTION]);
while ((ticket= trans_it++))
ticket->m_duration= MDL_TRANSACTION;
#endif
}
void MDL_context::release_explicit_locks()
{
release_locks_stored_before(MDL_EXPLICIT, NULL);
}
bool MDL_context::has_explicit_locks()
{
MDL_ticket *ticket = NULL;
Ticket_iterator it(m_tickets[MDL_EXPLICIT]);
while ((ticket = it++))
{
return true;
}
return false;
}
#ifdef WITH_WSREP
static
const char *wsrep_get_mdl_namespace_name(MDL_key::enum_mdl_namespace ns)
{
switch (ns)
{
case MDL_key::BACKUP : return "BACKUP";
case MDL_key::SCHEMA : return "SCHEMA";
case MDL_key::TABLE : return "TABLE";
case MDL_key::FUNCTION : return "FUNCTION";
case MDL_key::PROCEDURE : return "PROCEDURE";
case MDL_key::PACKAGE_BODY: return "PACKAGE BODY";
case MDL_key::TRIGGER : return "TRIGGER";
case MDL_key::EVENT : return "EVENT";
case MDL_key::USER_LOCK : return "USER_LOCK";
default: break;
}
return "UNKNOWN";
}
void MDL_ticket::wsrep_report(bool debug) const
{
if (!debug) return;
const PSI_stage_info *psi_stage= get_key()->get_wait_state_name();
WSREP_DEBUG("MDL ticket: type: %s space: %s db: %s name: %s (%s)",
get_type_name()->str,
wsrep_get_mdl_namespace_name(get_key()->mdl_namespace()),
get_key()->db_name(),
get_key()->name(),
psi_stage->m_name);
}
#endif /* WITH_WSREP */
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