mirror of
https://git.postgresql.org/git/postgresql.git
synced 2026-02-22 22:37:01 +08:00
8214667226
Previously, ReplicationSlotsComputeRequiredXmin() computed the oldest xmin across all slots without holding ProcArrayLock (when already_locked is false), acquiring the lock just before updating the replication slot xmin. This could lead to a race condition: if a backend created a new slot and updates the global replication slot xmin, another backend concurrently running ReplicationSlotsComputeRequiredXmin() could overwrite that update with an invalid or stale value. This happens because the concurrent backend might have computed the aggregate xmin before the new slot was accounted for, but applied the update after the new slot had already updated the global value. In the reported failure, a walsender for an apply worker computed InvalidTransactionId as the oldest xmin and overwrote a valid replication slot xmin value computed by a walsender for a tablesync worker. Consequently, the tablesync worker computed a transaction ID via GetOldestSafeDecodingTransactionId() effectively without considering the replication slot xmin. This led to the error "cannot build an initial slot snapshot as oldest safe xid %u follows snapshot's xmin %u", which was an assertion failure prior to commit 240e0dbacd3. To fix this, we acquire ReplicationSlotControlLock in exclusive mode during slot creation to perform the initial update of the slot xmin. In ReplicationSlotsComputeRequiredXmin(), we hold ReplicationSlotControlLock in shared mode until the global slot xmin is updated in ProcArraySetReplicationSlotXmin(). This prevents concurrent computations and updates of the global xmin by other backends during the initial slot xmin update process, while still permitting concurrent calls to ReplicationSlotsComputeRequiredXmin(). Backpatch to all supported versions. Author: Zhijie Hou <houzj.fnst@fujitsu.com> Reviewed-by: Masahiko Sawada <sawada.mshk@gmail.com> Reviewed-by: Amit Kapila <amit.kapila16@gmail.com> Reviewed-by: Pradeep Kumar <spradeepkumar29@gmail.com> Reviewed-by: Hayato Kuroda (Fujitsu) <kuroda.hayato@fujitsu.com> Reviewed-by: Robert Haas <robertmhaas@gmail.com> Reviewed-by: Andres Freund <andres@anarazel.de> Reviewed-by: Chao Li <li.evan.chao@gmail.com> Discussion: https://postgr.es/m/CAA4eK1L8wYcyTPxNzPGkhuO52WBGoOZbT0A73Le=ZUWYAYmdfw@mail.gmail.com Backpatch-through: 14
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. PostgreSQL has many language interfaces, many of which are listed here: https://www.postgresql.org/download/ See the file INSTALL for instructions on how to build and install PostgreSQL. That file also lists supported operating systems and hardware platforms and contains information regarding any other software packages that are required to build or run the PostgreSQL system. Copyright and license information can be found in the file COPYRIGHT. A comprehensive documentation set is included in this distribution; it can be read as described in the installation instructions. The latest version of this software may be obtained at https://www.postgresql.org/download/. For more information look at our web site located at https://www.postgresql.org/.