Collect statistics about conflicts in logical replication.

This commit adds columns in view pg_stat_subscription_stats to show the
number of times a particular conflict type has occurred during the
application of logical replication changes. The following columns are
added:

confl_insert_exists:
        Number of times a row insertion violated a NOT DEFERRABLE unique
        constraint.
confl_update_origin_differs:
        Number of times an update was performed on a row that was
        previously modified by another origin.
confl_update_exists:
        Number of times that the updated value of a row violates a
        NOT DEFERRABLE unique constraint.
confl_update_missing:
        Number of times that the tuple to be updated is missing.
confl_delete_origin_differs:
        Number of times a delete was performed on a row that was
        previously modified by another origin.
confl_delete_missing:
        Number of times that the tuple to be deleted is missing.

The update_origin_differs and delete_origin_differs conflicts can be
detected only when track_commit_timestamp is enabled.

Author: Hou Zhijie
Reviewed-by: Shveta Malik, Peter Smith, Anit Kapila
Discussion: https://postgr.es/m/OS0PR01MB57160A07BD575773045FC214948F2@OS0PR01MB5716.jpnprd01.prod.outlook.com

1 files changed, 4 insertions, 0 deletions

diff --git a/src/include/pgstat.h b/src/include/pgstat.h
index f63159c55ca..be2c91168a1 100644
--- a/src/include/pgstat.h
+++ b/src/include/pgstat.h
@@ -15,6 +15,7 @@
 #include "datatype/timestamp.h"
 #include "portability/instr_time.h"
 #include "postmaster/pgarch.h"	/* for MAX_XFN_CHARS */
+#include "replication/conflict.h"
 #include "utils/backend_progress.h" /* for backward compatibility */
 #include "utils/backend_status.h"	/* for backward compatibility */
 #include "utils/relcache.h"
@@ -165,6 +166,7 @@ typedef struct PgStat_BackendSubEntry
 {
 	PgStat_Counter apply_error_count;
 	PgStat_Counter sync_error_count;
+	PgStat_Counter conflict_count[CONFLICT_NUM_TYPES];
 } PgStat_BackendSubEntry;
 
 /* ----------
@@ -423,6 +425,7 @@ typedef struct PgStat_StatSubEntry
 {
 	PgStat_Counter apply_error_count;
 	PgStat_Counter sync_error_count;
+	PgStat_Counter conflict_count[CONFLICT_NUM_TYPES];
 	TimestampTz stat_reset_timestamp;
 } PgStat_StatSubEntry;
 
@@ -725,6 +728,7 @@ extern PgStat_SLRUStats *pgstat_fetch_slru(void);
  */
 
 extern void pgstat_report_subscription_error(Oid subid, bool is_apply_error);
+extern void pgstat_report_subscription_conflict(Oid subid, ConflictType type);
 extern void pgstat_create_subscription(Oid subid);
 extern void pgstat_drop_subscription(Oid subid);
 extern PgStat_StatSubEntry *pgstat_fetch_stat_subscription(Oid subid);