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Commit7c906c5

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author
Amit Kapila
committed
Doc: Fix pg_copy_logical_replication_slot description.
This commit documents that the failover option is not copied when usingthe pg_copy_logical_replication_slot function.In passing, we modify the comments in the function clarifying the reasonfor this behavior.Reported-by: <duffieldzane@gmail.com>Author: Hou Zhijie <houzj.fnst@fujitsu.com>Reviewed-by: Amit Kapila <amit.kapila16@gmail.com>Backpatch-through: 17, where it was introducedDiscussion:https://postgr.es/m/173976850802.682632.11315364077431550250@wrigleys.postgresql.org
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‎doc/src/sgml/func.sgml

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@@ -29118,6 +29118,10 @@ postgres=# SELECT '0/0'::pg_lsn + pd.segment_number * ps.setting::int + :offset
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from the same <acronym>LSN</acronym> as the source logical slot. Both
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<parameter>temporary</parameter> and <parameter>plugin</parameter> are
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optional; if they are omitted, the values of the source slot are used.
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The <literal>failover</literal> option of the source logical slot
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is not copied and is set to <literal>false</literal> by default. This
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is to avoid the risk of being unable to continue logical replication
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after failover to standby where the slot is being synchronized.
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</para></entry>
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</row>
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‎src/backend/replication/slotfuncs.c

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@@ -698,13 +698,18 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
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* hence pass find_startpoint false. confirmed_flush will be set
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* below, by copying from the source slot.
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*
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* To avoid potential issues with the slot synchronization where the
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* restart_lsn of a replication slot can go backward, we set the
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* failover option to false here. This situation occurs when a slot
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* on the primary server is dropped and immediately replaced with a
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* new slot of the same name, created by copying from another existing
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* slot. However, the slot synchronization will only observe the
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* restart_lsn of the same slot going backward.
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* We don't copy the failover option to prevent potential issues with
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* slot synchronization. For instance, if a slot was synchronized to
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* the standby, then dropped on the primary, and immediately recreated
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* by copying from another existing slot with much earlier restart_lsn
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* and confirmed_flush_lsn, the slot synchronization would only
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* observe the LSN of the same slot moving backward. As slot
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* synchronization does not copy the restart_lsn and
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* confirmed_flush_lsn backward (see update_local_synced_slot() for
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* details), if a failover happens before the primary's slot catches
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* up, logical replication cannot continue using the synchronized slot
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* on the promoted standby because the slot retains the restart_lsn
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* and confirmed_flush_lsn that are much later than expected.
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*/
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create_logical_replication_slot(NameStr(*dst_name),
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plugin,

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