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The DROP SUBSCRIPTION command performs several operations: it stops the subscription workers, removes subscription-related entries from system catalogs, and deletes the replication slot on the publisher server. Previously, this command acquired an AccessExclusiveLock on pg_subscription before initiating these steps. However, while holding this lock, the command attempts to connect to the publisher to remove the replication slot. In cases where the connection is made to a newly created database on the same server as subscriber, the cache-building process during connection tries to acquire an AccessShareLock on pg_subscription, resulting in a self-deadlock. To resolve this issue, we reduce the lock level on pg_subscription during DROP SUBSCRIPTION from AccessExclusiveLock to RowExclusiveLock. Earlier, the higher lock level was used to prevent the launcher from starting a new worker during the drop operation, as a restarted worker could become orphaned. Now, instead of relying on a strict lock, we acquire an AccessShareLock on the specific subscription being dropped and re-validate its existence after acquiring the lock. If the subscription is no longer valid, the worker exits gracefully. This approach avoids the deadlock while still ensuring that orphan workers are not created. Reported-by: Alexander Lakhin <exclusion@gmail.com> Author: Dilip Kumar <dilipbalaut@gmail.com> Reviewed-by: vignesh C <vignesh21@gmail.com> Reviewed-by: Hayato Kuroda <kuroda.hayato@fujitsu.com> Reviewed-by: Amit Kapila <amit.kapila16@gmail.com> Backpatch-through: 13 Discussion: https://postgr.es/m/18988-7312c868be2d467f@postgresql.org |
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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/.