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A race condition could cause a newly created replication slot to become invalidated between WAL reservation and a checkpoint. Previously, if the required WAL was removed, we retried the reservation process. However, the slot could still be invalidated before the retry if the WAL was not yet removed but the checkpoint advanced the redo pointer beyond the slot's intended restart LSN and computed the minimum LSN that needs to be preserved for the slots. The fix is to acquire an exclusive lock on ReplicationSlotAllocationLock during WAL reservation, and a shared lock during the minimum LSN calculation at checkpoints to serialize the process. This ensures that, if WAL reservation occurs first, the checkpoint waits until restart_lsn is updated before calculating the minimum LSN. If the checkpoint runs first, subsequent WAL reservations pick a position at or after the latest checkpoint's redo pointer. We used a similar fix in HEAD (via commit 006dd4b2e5) and 18. The difference is that in 17 and prior branches we need to additionally handle the race condition with slot's minimum LSN computation during checkpoints. Reported-by: suyu.cmj <mengjuan.cmj@alibaba-inc.com> Author: Hou Zhijie <houzj.fnst@fujitsu.com> Author: vignesh C <vignesh21@gmail.com> Reviewed-by: Hayato Kuroda <kuroda.hayato@fujitsu.com> Reviewed-by: Masahiko Sawada <sawada.mshk@gmail.com> Reviewed-by: Amit Kapila <amit.kapila16@gmail.com> Backpatch-through: 14 Discussion: https://postgr.es/m/5e045179-236f-4f8f-84f1-0f2566ba784c.mengjuan.cmj@alibaba-inc.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. 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/.