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Introduce a new GUC 'standby_slot_names'.

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This patch provides a way to ensure that physical standbys that are
potential failover candidates have received and flushed changes before
the primary server making them visible to subscribers. Doing so guarantees
that the promoted standby server is not lagging behind the subscribers
when a failover is necessary.

The logical walsender now guarantees that all local changes are sent and
flushed to the standby servers corresponding to the replication slots
specified in 'standby_slot_names' before sending those changes to the
subscriber.

Additionally, the SQL functions pg_logical_slot_get_changes,
pg_logical_slot_peek_changes and pg_replication_slot_advance are modified
to ensure that they process changes for failover slots only after physical
slots specified in 'standby_slot_names' have confirmed WAL receipt for those.

Author: Hou Zhijie and Shveta Malik
Reviewed-by: Masahiko Sawada, Peter Smith, Bertrand Drouvot, Ajin Cherian, Nisha Moond, Amit Kapila
Discussion: https://postgr.es/m/514f6f2f-6833-4539-39f1-96cd1e011f23@enterprisedb.com
This commit is contained in:
Amit Kapila
2024-03-08 08:10:45 +05:30
parent 453c468737
commit bf279ddd1c
18 changed files with 918 additions and 27 deletions
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5
src/include/replication/slot.h
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@@ -226,6 +226,7 @@ extern PGDLLIMPORT ReplicationSlot *MyReplicationSlot;
/* GUCs */
extern PGDLLIMPORT int max_replication_slots;
extern PGDLLIMPORT char *standby_slot_names;
/* shmem initialization functions */
extern Size ReplicationSlotsShmemSize(void);
@@ -274,4 +275,8 @@ extern void CheckSlotPermissions(void);
extern ReplicationSlotInvalidationCause
GetSlotInvalidationCause(const char *conflict_reason);
extern bool SlotExistsInStandbySlotNames(const char *slot_name);
extern bool StandbySlotsHaveCaughtup(XLogRecPtr wait_for_lsn, int elevel);
extern void WaitForStandbyConfirmation(XLogRecPtr wait_for_lsn);
#endif /* SLOT_H */

1
src/include/replication/walsender.h
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@@ -39,6 +39,7 @@ extern void InitWalSender(void);
extern bool exec_replication_command(const char *cmd_string);
extern void WalSndErrorCleanup(void);
extern void WalSndResourceCleanup(bool isCommit);
extern void PhysicalWakeupLogicalWalSnd(void);
extern XLogRecPtr GetStandbyFlushRecPtr(TimeLineID *tli);
extern void WalSndSignals(void);
extern Size WalSndShmemSize(void);

7
src/include/replication/walsender_private.h
View File

@@ -113,6 +113,13 @@ typedef struct
ConditionVariable wal_flush_cv;
ConditionVariable wal_replay_cv;
/*
* Used by physical walsenders holding slots specified in
* standby_slot_names to wake up logical walsenders holding logical
* failover slots when a walreceiver confirms the receipt of LSN.
*/
ConditionVariable wal_confirm_rcv_cv;
WalSnd walsnds[FLEXIBLE_ARRAY_MEMBER];
} WalSndCtlData;