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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 If the subscription is no longer valid, the worker exits gracefully.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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