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Flush logical slots to disk during a shutdown checkpoint if required.

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It's entirely possible for a logical slot to have a confirmed_flush LSN
higher than the last value saved on disk while not being marked as dirty.
Currently, it is not a major problem but a later patch adding support for
the upgrade of slots relies on that value being properly flushed to disk.

It can also help avoid processing the same transactions again in some
boundary cases after the clean shutdown and restart.  Say, we process
some transactions for which we didn't send anything downstream (the
changes got filtered) but the confirm_flush LSN is updated due to
keepalives.  As we don't flush the latest value of confirm_flush LSN, it
may lead to processing the same changes again without this patch.

The approach taken by this patch has been suggested by Ashutosh Bapat.

Author: Vignesh C, Julien Rouhaud, Kuroda Hayato
Reviewed-by: Amit Kapila, Dilip Kumar, Michael Paquier, Ashutosh Bapat, Peter Smith, Hou Zhijie
Discussion: http://postgr.es/m/CAA4eK1JzJagMmb_E8D4au=GYQkxox0AfNBm1FbP7sy7t4YWXPQ@mail.gmail.com
Discussion: http://postgr.es/m/TYAPR01MB58664C81887B3AF2EB6B16E3F5939@TYAPR01MB5866.jpnprd01.prod.outlook.com
This commit is contained in:
Amit Kapila
2023-09-14 08:56:13 +05:30
parent a2e0d5e5f6
commit e0b2eed047
5 changed files with 145 additions and 6 deletions
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9
src/include/replication/slot.h
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@@ -178,6 +178,13 @@ typedef struct ReplicationSlot
XLogRecPtr candidate_xmin_lsn;
XLogRecPtr candidate_restart_valid;
XLogRecPtr candidate_restart_lsn;
/*
* This value tracks the last confirmed_flush LSN flushed which is used
* during a shutdown checkpoint to decide if logical's slot data should be
* forcibly flushed or not.
*/
XLogRecPtr last_saved_confirmed_flush;
} ReplicationSlot;
#define SlotIsPhysical(slot) ((slot)->data.database == InvalidOid)
@@ -241,7 +248,7 @@ extern void ReplicationSlotNameForTablesync(Oid suboid, Oid relid, char *syncslo
extern void ReplicationSlotDropAtPubNode(WalReceiverConn *wrconn, char *slotname, bool missing_ok);
extern void StartupReplicationSlots(void);
extern void CheckPointReplicationSlots(void);
extern void CheckPointReplicationSlots(bool is_shutdown);
extern void CheckSlotRequirements(void);
extern void CheckSlotPermissions(void);