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Logical replication requires reliable conflict detection to maintain data consistency across nodes. To achieve this, we must prevent premature removal of tuples deleted by other origins and their associated commit_ts data by VACUUM, which could otherwise lead to incorrect conflict reporting and resolution. This patch introduces a mechanism to retain deleted tuples on the subscriber during the application of concurrent transactions from remote nodes. Retaining these tuples allows us to correctly ignore concurrent updates to the same tuple. Without this, an UPDATE might be misinterpreted as an INSERT during resolutions due to the absence of the original tuple. Additionally, we ensure that origin metadata is not prematurely removed by vacuum freeze, which is essential for detecting update_origin_differs and delete_origin_differs conflicts. To support this, a new replication slot named pg_conflict_detection is created and maintained by the launcher on the subscriber. Each apply worker tracks its own non-removable transaction ID, which the launcher aggregates to determine the appropriate xmin for the slot, thereby retaining necessary tuples. Conflict information retention (deleted tuples and commit_ts) can be enabled per subscription via the retain_conflict_info option. This is disabled by default to avoid unnecessary overhead for configurations that do not require conflict resolution or logging. During upgrades, if any subscription on the old cluster has retain_conflict_info enabled, a conflict detection slot will be created to protect relevant tuples from deletion when the new cluster starts. This is a foundational work to correctly detect update_deleted conflict which will be done in a follow-up patch. Author: Zhijie Hou <houzj.fnst@fujitsu.com> Reviewed-by: shveta malik <shveta.malik@gmail.com> Reviewed-by: Masahiko Sawada <sawada.mshk@gmail.com> Reviewed-by: Dilip Kumar <dilipbalaut@gmail.com> Reviewed-by: Nisha Moond <nisha.moond412@gmail.com> Reviewed-by: Amit Kapila <amit.kapila16@gmail.com> Discussion: https://postgr.es/m/OS0PR01MB5716BE80DAEB0EE2A6A5D1F5949D2@OS0PR01MB5716.jpnprd01.prod.outlook.com
PostgreSQL Database Management System
This directory contains the source code distribution of the PostgreSQL database management system.
PostgreSQL is an advanced object-relational database management system that supports an extended subset of the SQL standard, including transactions, foreign keys, subqueries, triggers, user-defined types and functions. This distribution also contains C language bindings.
Copyright and license information can be found in the file COPYRIGHT.
General documentation about this version of PostgreSQL can be found at https://www.postgresql.org/docs/devel/. In particular, information about building PostgreSQL from the source code can be found at https://www.postgresql.org/docs/devel/installation.html.
The latest version of this software, and related software, may be obtained at https://www.postgresql.org/download/. For more information look at our web site located at https://www.postgresql.org/.