Reconsider pg_stat_subscription_workers view.

It was decided (refer to the Discussion link below) that the stats
collector is not an appropriate place to store the error information of
subscription workers.

This patch changes the pg_stat_subscription_workers view (introduced by
commit 8d74fc96db) so that it stores only statistics counters:
apply_error_count and sync_error_count, and has one entry for
each subscription. The removed error information such as error-XID and
the error message would be stored in another way in the future which is
more reliable and persistent.

After removing these error details, there is no longer any relation
information, so the subscription statistics are now a cluster-wide
statistics.

The patch also changes the view name to pg_stat_subscription_stats since
the word "worker" is an implementation detail that we use one worker for
one tablesync and one apply.

Author: Masahiko Sawada, based on suggestions by Andres Freund
Reviewed-by: Peter Smith, Haiying Tang, Takamichi Osumi, Amit Kapila
Discussion: https://postgr.es/m/20220125063131.4cmvsxbz2tdg6g65@alap3.anarazel.de

1 files changed, 59 insertions, 97 deletions

diff --git a/src/backend/utils/adt/pgstatfuncs.c b/src/backend/utils/adt/pgstatfuncs.c
index 30e8dfa7c12..fd993d0d5fb 100644
--- a/src/backend/utils/adt/pgstatfuncs.c
+++ b/src/backend/utils/adt/pgstatfuncs.c
@@ -2163,7 +2163,7 @@ pg_stat_reset_single_table_counters(PG_FUNCTION_ARGS)
 {
 	Oid			taboid = PG_GETARG_OID(0);
 
-	pgstat_reset_single_counter(taboid, InvalidOid, RESET_TABLE);
+	pgstat_reset_single_counter(taboid, RESET_TABLE);
 
 	PG_RETURN_VOID();
 }
@@ -2173,38 +2173,11 @@ pg_stat_reset_single_function_counters(PG_FUNCTION_ARGS)
 {
 	Oid			funcoid = PG_GETARG_OID(0);
 
-	pgstat_reset_single_counter(funcoid, InvalidOid, RESET_FUNCTION);
+	pgstat_reset_single_counter(funcoid, RESET_FUNCTION);
 
 	PG_RETURN_VOID();
 }
 
-Datum
-pg_stat_reset_subscription_worker_subrel(PG_FUNCTION_ARGS)
-{
-	Oid			subid = PG_GETARG_OID(0);
-	Oid			relid = PG_ARGISNULL(1) ? InvalidOid : PG_GETARG_OID(1);
-
-	pgstat_reset_single_counter(subid, relid, RESET_SUBWORKER);
-
-	PG_RETURN_VOID();
-}
-
-/* Reset all subscription worker stats associated with the given subscription */
-Datum
-pg_stat_reset_subscription_worker_sub(PG_FUNCTION_ARGS)
-{
-	Oid			subid = PG_GETARG_OID(0);
-
-	/*
-	 * Use subscription drop message to remove statistics of all subscription
-	 * workers.
-	 */
-	pgstat_report_subscription_drop(subid);
-
-	PG_RETURN_VOID();
-}
-
-
 /* Reset SLRU counters (a specific one or all of them). */
 Datum
 pg_stat_reset_slru(PG_FUNCTION_ARGS)
@@ -2258,6 +2231,32 @@ pg_stat_reset_replication_slot(PG_FUNCTION_ARGS)
 	PG_RETURN_VOID();
 }
 
+/* Reset subscription stats (a specific one or all of them) */
+Datum
+pg_stat_reset_subscription_stats(PG_FUNCTION_ARGS)
+{
+	Oid			subid;
+
+	if (PG_ARGISNULL(0))
+	{
+		/* Clear all subscription stats */
+		subid = InvalidOid;
+	}
+	else
+	{
+		subid = PG_GETARG_OID(0);
+
+		if (!OidIsValid(subid))
+			ereport(ERROR,
+					(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+					 errmsg("invalid subscription OID %u", subid)));
+	}
+
+	pgstat_reset_subscription_counter(subid);
+
+	PG_RETURN_VOID();
+}
+
 Datum
 pg_stat_get_archiver(PG_FUNCTION_ARGS)
 {
@@ -2400,50 +2399,32 @@ pg_stat_get_replication_slot(PG_FUNCTION_ARGS)
 }
 
 /*
- * Get the subscription worker statistics for the given subscription
- * (and relation).
+ * Get the subscription statistics for the given subscription. If the
+ * subscription statistics is not available, return all-zeros stats.
  */
 Datum
-pg_stat_get_subscription_worker(PG_FUNCTION_ARGS)
+pg_stat_get_subscription_stats(PG_FUNCTION_ARGS)
 {
-#define PG_STAT_GET_SUBSCRIPTION_WORKER_COLS	8
+#define PG_STAT_GET_SUBSCRIPTION_STATS_COLS	4
 	Oid			subid = PG_GETARG_OID(0);
-	Oid			subrelid;
 	TupleDesc	tupdesc;
-	Datum		values[PG_STAT_GET_SUBSCRIPTION_WORKER_COLS];
-	bool		nulls[PG_STAT_GET_SUBSCRIPTION_WORKER_COLS];
-	PgStat_StatSubWorkerEntry *wentry;
-	int			i;
-
-	if (PG_ARGISNULL(1))
-		subrelid = InvalidOid;
-	else
-		subrelid = PG_GETARG_OID(1);
+	Datum		values[PG_STAT_GET_SUBSCRIPTION_STATS_COLS];
+	bool		nulls[PG_STAT_GET_SUBSCRIPTION_STATS_COLS];
+	PgStat_StatSubEntry *subentry;
+	PgStat_StatSubEntry allzero;
 
-	/* Get subscription worker stats */
-	wentry = pgstat_fetch_stat_subworker_entry(subid, subrelid);
-
-	/* Return NULL if there is no worker statistics */
-	if (wentry == NULL)
-		PG_RETURN_NULL();
+	/* Get subscription stats */
+	subentry = pgstat_fetch_stat_subscription(subid);
 
 	/* Initialise attributes information in the tuple descriptor */
-	tupdesc = CreateTemplateTupleDesc(PG_STAT_GET_SUBSCRIPTION_WORKER_COLS);
+	tupdesc = CreateTemplateTupleDesc(PG_STAT_GET_SUBSCRIPTION_STATS_COLS);
 	TupleDescInitEntry(tupdesc, (AttrNumber) 1, "subid",
 					   OIDOID, -1, 0);
-	TupleDescInitEntry(tupdesc, (AttrNumber) 2, "subrelid",
-					   OIDOID, -1, 0);
-	TupleDescInitEntry(tupdesc, (AttrNumber) 3, "last_error_relid",
-					   OIDOID, -1, 0);
-	TupleDescInitEntry(tupdesc, (AttrNumber) 4, "last_error_command",
-					   TEXTOID, -1, 0);
-	TupleDescInitEntry(tupdesc, (AttrNumber) 5, "last_error_xid",
-					   XIDOID, -1, 0);
-	TupleDescInitEntry(tupdesc, (AttrNumber) 6, "last_error_count",
+	TupleDescInitEntry(tupdesc, (AttrNumber) 2, "apply_error_count",
 					   INT8OID, -1, 0);
-	TupleDescInitEntry(tupdesc, (AttrNumber) 7, "last_error_message",
-					   TEXTOID, -1, 0);
-	TupleDescInitEntry(tupdesc, (AttrNumber) 8, "last_error_time",
+	TupleDescInitEntry(tupdesc, (AttrNumber) 3, "sync_error_count",
+					   INT8OID, -1, 0);
+	TupleDescInitEntry(tupdesc, (AttrNumber) 4, "stats_reset",
 					   TIMESTAMPTZOID, -1, 0);
 	BlessTupleDesc(tupdesc);
 
@@ -2451,46 +2432,27 @@ pg_stat_get_subscription_worker(PG_FUNCTION_ARGS)
 	MemSet(values, 0, sizeof(values));
 	MemSet(nulls, 0, sizeof(nulls));
 
-	i = 0;
-	/* subid */
-	values[i++] = ObjectIdGetDatum(subid);
-
-	/* subrelid */
-	if (OidIsValid(subrelid))
-		values[i++] = ObjectIdGetDatum(subrelid);
-	else
-		nulls[i++] = true;
-
-	/* last_error_relid */
-	if (OidIsValid(wentry->last_error_relid))
-		values[i++] = ObjectIdGetDatum(wentry->last_error_relid);
-	else
-		nulls[i++] = true;
-
-	/* last_error_command */
-	if (wentry->last_error_command != 0)
-		values[i++] =
-			CStringGetTextDatum(logicalrep_message_type(wentry->last_error_command));
-	else
-		nulls[i++] = true;
+	if (!subentry)
+	{
+		/* If the subscription is not found, initialise its stats */
+		memset(&allzero, 0, sizeof(PgStat_StatSubEntry));
+		subentry = &allzero;
+	}
 
-	/* last_error_xid */
-	if (TransactionIdIsValid(wentry->last_error_xid))
-		values[i++] = TransactionIdGetDatum(wentry->last_error_xid);
-	else
-		nulls[i++] = true;
+	/* subid */
+	values[0] = ObjectIdGetDatum(subid);
 
-	/* last_error_count */
-	values[i++] = Int64GetDatum(wentry->last_error_count);
+	/* apply_error_count */
+	values[1] = Int64GetDatum(subentry->apply_error_count);
 
-	/* last_error_message */
-	values[i++] = CStringGetTextDatum(wentry->last_error_message);
+	/* sync_error_count */
+	values[2] = Int64GetDatum(subentry->sync_error_count);
 
-	/* last_error_time */
-	if (wentry->last_error_time != 0)
-		values[i++] = TimestampTzGetDatum(wentry->last_error_time);
+	/* stats_reset */
+	if (subentry->stat_reset_timestamp == 0)
+		nulls[3] = true;
 	else
-		nulls[i++] = true;
+		values[3] = TimestampTzGetDatum(subentry->stat_reset_timestamp);
 
 	/* Returns the record as Datum */
 	PG_RETURN_DATUM(HeapTupleGetDatum(heap_form_tuple(tupdesc, values, nulls)));