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authorAmit Kapila2025-02-25 04:12:07 +0000
committerAmit Kapila2025-02-25 04:12:07 +0000
commit5b8f2ccc0a93375acb64a457817e61f400404a1f (patch)
treeed3312e21230ca9524c6d63535e1f5b902e75464
parent15601fa21a5509b83a871c39ab98671f560da905 (diff)
Doc: Fix pg_copy_logical_replication_slot description.
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: <[email protected]> Author: Hou Zhijie <[email protected]> Reviewed-by: Amit Kapila <[email protected]> Backpatch-through: 17, where it was introduced Discussion: https://postgr.es/m/[email protected]
-rw-r--r--doc/src/sgml/func.sgml4
-rw-r--r--src/backend/replication/slotfuncs.c19
2 files changed, 16 insertions, 7 deletions
diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml
index 21a8ea42f5f..f0ccb751106 100644
--- 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 f652ec8a73e..146eef5871e 100644
--- 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,