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, 26 insertions, 7 deletions

diff --git a/src/backend/utils/adt/pgstatfuncs.c b/src/backend/utils/adt/pgstatfuncs.c
index 32211371237..97dc09ac0d9 100644
--- a/src/backend/utils/adt/pgstatfuncs.c
+++ b/src/backend/utils/adt/pgstatfuncs.c
@@ -1966,13 +1966,14 @@ pg_stat_get_replication_slot(PG_FUNCTION_ARGS)
 Datum
 pg_stat_get_subscription_stats(PG_FUNCTION_ARGS)
 {
-#define PG_STAT_GET_SUBSCRIPTION_STATS_COLS	4
+#define PG_STAT_GET_SUBSCRIPTION_STATS_COLS	10
 	Oid			subid = PG_GETARG_OID(0);
 	TupleDesc	tupdesc;
 	Datum		values[PG_STAT_GET_SUBSCRIPTION_STATS_COLS] = {0};
 	bool		nulls[PG_STAT_GET_SUBSCRIPTION_STATS_COLS] = {0};
 	PgStat_StatSubEntry *subentry;
 	PgStat_StatSubEntry allzero;
+	int			i = 0;
 
 	/* Get subscription stats */
 	subentry = pgstat_fetch_stat_subscription(subid);
@@ -1985,7 +1986,19 @@ pg_stat_get_subscription_stats(PG_FUNCTION_ARGS)
 					   INT8OID, -1, 0);
 	TupleDescInitEntry(tupdesc, (AttrNumber) 3, "sync_error_count",
 					   INT8OID, -1, 0);
-	TupleDescInitEntry(tupdesc, (AttrNumber) 4, "stats_reset",
+	TupleDescInitEntry(tupdesc, (AttrNumber) 4, "confl_insert_exists",
+					   INT8OID, -1, 0);
+	TupleDescInitEntry(tupdesc, (AttrNumber) 5, "confl_update_origin_differs",
+					   INT8OID, -1, 0);
+	TupleDescInitEntry(tupdesc, (AttrNumber) 6, "confl_update_exists",
+					   INT8OID, -1, 0);
+	TupleDescInitEntry(tupdesc, (AttrNumber) 7, "confl_update_missing",
+					   INT8OID, -1, 0);
+	TupleDescInitEntry(tupdesc, (AttrNumber) 8, "confl_delete_origin_differs",
+					   INT8OID, -1, 0);
+	TupleDescInitEntry(tupdesc, (AttrNumber) 9, "confl_delete_missing",
+					   INT8OID, -1, 0);
+	TupleDescInitEntry(tupdesc, (AttrNumber) 10, "stats_reset",
 					   TIMESTAMPTZOID, -1, 0);
 	BlessTupleDesc(tupdesc);
 
@@ -1997,19 +2010,25 @@ pg_stat_get_subscription_stats(PG_FUNCTION_ARGS)
 	}
 
 	/* subid */
-	values[0] = ObjectIdGetDatum(subid);
+	values[i++] = ObjectIdGetDatum(subid);
 
 	/* apply_error_count */
-	values[1] = Int64GetDatum(subentry->apply_error_count);
+	values[i++] = Int64GetDatum(subentry->apply_error_count);
 
 	/* sync_error_count */
-	values[2] = Int64GetDatum(subentry->sync_error_count);
+	values[i++] = Int64GetDatum(subentry->sync_error_count);
+
+	/* conflict count */
+	for (int nconflict = 0; nconflict < CONFLICT_NUM_TYPES; nconflict++)
+		values[i++] = Int64GetDatum(subentry->conflict_count[nconflict]);
 
 	/* stats_reset */
 	if (subentry->stat_reset_timestamp == 0)
-		nulls[3] = true;
+		nulls[i] = true;
 	else
-		values[3] = TimestampTzGetDatum(subentry->stat_reset_timestamp);
+		values[i] = TimestampTzGetDatum(subentry->stat_reset_timestamp);
+
+	Assert(i + 1 == PG_STAT_GET_SUBSCRIPTION_STATS_COLS);
 
 	/* Returns the record as Datum */
 	PG_RETURN_DATUM(HeapTupleGetDatum(heap_form_tuple(tupdesc, values, nulls)));