Add a new slot sync worker to synchronize logical slots.

By enabling slot synchronization, all the failover logical replication
slots on the primary (assuming configurations are appropriate) are
automatically created on the physical standbys and are synced
periodically. The slot sync worker on the standby server pings the primary
server at regular intervals to get the necessary failover logical slots
information and create/update the slots locally. The slots that no longer
require synchronization are automatically dropped by the worker.

The nap time of the worker is tuned according to the activity on the
primary. The slot sync worker waits for some time before the next
synchronization, with the duration varying based on whether any slots were
updated during the last cycle.

A new parameter sync_replication_slots enables or disables this new
process.

On promotion, the slot sync worker is shut down by the startup process to
drop any temporary slots acquired by the slot sync worker and to prevent
the worker from trying to fetch the failover slots.

A functionality to allow logical walsenders to wait for the physical will
be done in a subsequent commit.

Author: Shveta Malik, Hou Zhijie based on design inputs by Masahiko Sawada and Amit Kapila
Reviewed-by: Masahiko Sawada, Bertrand Drouvot, Peter Smith, Dilip Kumar, Ajin Cherian, Nisha Moond, Kuroda Hayato, Amit Kapila
Discussion: https://postgr.es/m/514f6f2f-6833-4539-39f1-96cd1e011f23@enterprisedb.com

2 files changed, 21 insertions, 1 deletions

diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 0445fbf61d7..612fb5f42e0 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -333,6 +333,7 @@ typedef enum BackendType
 	B_BG_WRITER,
 	B_CHECKPOINTER,
 	B_LOGGER,
+	B_SLOTSYNC_WORKER,
 	B_STANDALONE_BACKEND,
 	B_STARTUP,
 	B_WAL_RECEIVER,
diff --git a/src/include/replication/slotsync.h b/src/include/replication/slotsync.h
index e86d8a47b85..726d65f9b62 100644
--- a/src/include/replication/slotsync.h
+++ b/src/include/replication/slotsync.h
@@ -14,8 +14,27 @@
 
 #include "replication/walreceiver.h"
 
-extern void ValidateSlotSyncParams(void);
+extern PGDLLIMPORT bool sync_replication_slots;
+
+/*
+ * GUCs needed by slot sync worker to connect to the primary
+ * server and carry on with slots synchronization.
+ */
+extern PGDLLIMPORT char *PrimaryConnInfo;
+extern PGDLLIMPORT char *PrimarySlotName;
+
+extern char *CheckAndGetDbnameFromConninfo(void);
+extern bool ValidateSlotSyncParams(int elevel);
+
+#ifdef EXEC_BACKEND
+extern void ReplSlotSyncWorkerMain(int argc, char *argv[]) pg_attribute_noreturn();
+#endif
+extern int	StartSlotSyncWorker(void);
+
+extern void ShutDownSlotSync(void);
+extern bool SlotSyncWorkerCanRestart(void);
 extern bool IsSyncingReplicationSlots(void);
+extern bool IsLogicalSlotSyncWorker(void);
 extern Size SlotSyncShmemSize(void);
 extern void SlotSyncShmemInit(void);
 extern void SyncReplicationSlots(WalReceiverConn *wrconn);