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Amit Kapila
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Add retry logic to pg_sync_replication_slots().
Previously, pg_sync_replication_slots() would finish without synchronizing slots that didn't meet requirements, rather than failing outright. This could leave some failover slots unsynchronized if required catalog rows or WAL segments were missing or at risk of removal, while the standby continued removing needed data. To address this, the function now waits for the primary slot to advance to a position where all required data is available on the standby before completing synchronization. It retries cyclically until all failover slots that existed on the primary at the start of the call are synchronized. Slots created after the function begins are not included. If the standby is promoted during this wait, the function exits gracefully and the temporary slots will be removed. Author: Ajin Cherian <itsajin@gmail.com> Author: Hou Zhijie <houzj.fnst@fujitsu.com> Reviewed-by: Shveta Malik <shveta.malik@gmail.com> Reviewed-by: Japin Li <japinli@hotmail.com> Reviewed-by: Ashutosh Bapat <ashutosh.bapat.oss@gmail.com> Reviewed-by: Ashutosh Sharma <ashu.coek88@gmail.com> Reviewed-by: Chao Li <li.evan.chao@gmail.com> Reviewed-by: Yilin Zhang <jiezhilove@126.com> Reviewed-by: Amit Kapila <amit.kapila16@gmail.com> Discussion: https://postgr.es/m/CAFPTHDZAA%2BgWDntpa5ucqKKba41%3DtXmoXqN3q4rpjO9cdxgQrw%40mail.gmail.com
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‎doc/src/sgml/func/func-admin.sgml‎

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@@ -1497,9 +1497,7 @@ postgres=# SELECT '0/0'::pg_lsn + pd.segment_number * ps.setting::int + :offset
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standby server. Temporary synced slots, if any, cannot be used for
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logical decoding and must be dropped after promotion. See
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<xref linkend="logicaldecoding-replication-slots-synchronization"/> for details.
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Note that this function is primarily intended for testing and
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debugging purposes and should be used with caution. Additionally,
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this function cannot be executed if
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Note that this function cannot be executed if
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<link linkend="guc-sync-replication-slots"><varname>
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sync_replication_slots</varname></link> is enabled and the slotsync
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worker is already running to perform the synchronization of slots.

‎doc/src/sgml/logicaldecoding.sgml‎

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@@ -405,15 +405,13 @@ postgres=# SELECT * from pg_logical_slot_get_changes('regression_slot', NULL, NU
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periodic synchronization of failover slots, they can also be manually
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synchronized using the <link linkend="pg-sync-replication-slots">
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<function>pg_sync_replication_slots</function></link> function on the standby.
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However, this function is primarily intended for testing and debugging and
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should be used with caution. Unlike automatic synchronization, it does not
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include cyclic retries, making it more prone to synchronization failures,
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particularly during initial sync scenarios where the required WAL files
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or catalog rows for the slot might have already been removed or are at risk
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of being removed on the standby. In contrast, automatic synchronization
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via <varname>sync_replication_slots</varname> provides continuous slot
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updates, enabling seamless failover and supporting high availability.
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Therefore, it is the recommended method for synchronizing slots.
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However, unlike automatic synchronization, it does not perform incremental
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updates. It retries cyclically until all the failover slots that existed on
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primary at the start of the function call are synchronized. Any slots created
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after the function begins will not be synchronized. In contrast, automatic
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synchronization via <varname>sync_replication_slots</varname> provides
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continuous slot updates, enabling seamless failover and supporting high
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availability. Therefore, it is the recommended method for synchronizing slots.
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</para>
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</note>
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