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Doc: Fix pg_copy_logical_replication_slot description.

author Amit Kapila <akapila@postgresql.org>

2025年2月25日 04:12:07 +0000 (09:42 +0530)

committer Amit Kapila <akapila@postgresql.org>

2025年2月25日 04:12:07 +0000 (09:42 +0530)

This commit documents that the failover option is not copied when using
the pg_copy_logical_replication_slot function.

In passing, we modify the comments in the function clarifying the reason
for 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 introduced
Discussion: https://postgr.es/m/173976850802.682632.11315364077431550250@wrigleys.postgresql.org

doc/src/sgml/func.sgml patch | blob | blame | history

src/backend/replication/slotfuncs.c patch | blob | blame | history

diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml

index 21a8ea42f5fcce577c4a89183b3a5650b685a798..f0ccb751106cb1bf6434ce7d517c8b4c8fce47aa 100644 (file)

--- a/doc/src/sgml/func.sgml

+++ b/doc/src/sgml/func.sgml

@@ -29374,6 +29374,10 @@ postgres=# SELECT '0/0'::pg_lsn + pd.segment_number * ps.setting::int + :offset

from the same <acronym>LSN</acronym> as the source logical slot. Both

<parameter>temporary</parameter> and <parameter>plugin</parameter> are

optional; if they are omitted, the values of the source slot are used.

+ The <literal>failover</literal> option of the source logical slot

+ is not copied and is set to <literal>false</literal> by default. This

+ is to avoid the risk of being unable to continue logical replication

+ after failover to standby where the slot is being synchronized.

</para></entry>

</row>

diff --git a/src/backend/replication/slotfuncs.c b/src/backend/replication/slotfuncs.c

index f652ec8a73e4562f5d5bf6cd8c78b29765fcd1ab..146eef5871e28067915cb644b3da07abbfb59759 100644 (file)

--- a/src/backend/replication/slotfuncs.c

+++ b/src/backend/replication/slotfuncs.c

@@ -695,13 +695,18 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)

* hence pass find_startpoint false. confirmed_flush will be set

* below, by copying from the source slot.

- * To avoid potential issues with the slot synchronization where the

- * restart_lsn of a replication slot can go backward, we set the

- * failover option to false here. This situation occurs when a slot

- * on the primary server is dropped and immediately replaced with a

- * new slot of the same name, created by copying from another existing

- * slot. However, the slot synchronization will only observe the

- * restart_lsn of the same slot going backward.

+ * We don't copy the failover option to prevent potential issues with

+ * slot synchronization. For instance, if a slot was synchronized to

+ * the standby, then dropped on the primary, and immediately recreated

+ * by copying from another existing slot with much earlier restart_lsn

+ * and confirmed_flush_lsn, the slot synchronization would only

+ * observe the LSN of the same slot moving backward. As slot

+ * synchronization does not copy the restart_lsn and

+ * confirmed_flush_lsn backward (see update_local_synced_slot() for

+ * details), if a failover happens before the primary's slot catches

+ * up, logical replication cannot continue using the synchronized slot

+ * on the promoted standby because the slot retains the restart_lsn

+ * and confirmed_flush_lsn that are much later than expected.

create_logical_replication_slot(NameStr(*dst_name),

plugin,

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