Track statistics for spilling of changes from ReorderBuffer.

This adds the statistics about transactions spilled to disk from
ReorderBuffer. Users can query the pg_stat_replication_slots view to check
these stats and call pg_stat_reset_replication_slot to reset the stats of
a particular slot. Users can pass NULL in pg_stat_reset_replication_slot
to reset stats of all the slots.

This commit extends the statistics collector to track this information
about slots.

Author: Sawada Masahiko and Amit Kapila
Reviewed-by: Amit Kapila and Dilip Kumar
Discussion: https://postgr.es/m/CA+fd4k5_pPAYRTDrO2PbtTOe0eHQpBvuqmCr8ic39uTNmR49Eg@mail.gmail.com

1 files changed, 80 insertions, 0 deletions

diff --git a/src/backend/utils/adt/pgstatfuncs.c b/src/backend/utils/adt/pgstatfuncs.c
index 24e191ea30b..0d0d2e6d2bb 100644
--- a/src/backend/utils/adt/pgstatfuncs.c
+++ b/src/backend/utils/adt/pgstatfuncs.c
@@ -2069,6 +2069,20 @@ pg_stat_reset_slru(PG_FUNCTION_ARGS)
 	PG_RETURN_VOID();
 }
 
+/* Reset replication slots stats (a specific one or all of them). */
+Datum
+pg_stat_reset_replication_slot(PG_FUNCTION_ARGS)
+{
+	char	   *target = NULL;
+
+	if (!PG_ARGISNULL(0))
+		target = text_to_cstring(PG_GETARG_TEXT_PP(0));
+
+	pgstat_reset_replslot_counter(target);
+
+	PG_RETURN_VOID();
+}
+
 Datum
 pg_stat_get_archiver(PG_FUNCTION_ARGS)
 {
@@ -2134,3 +2148,69 @@ pg_stat_get_archiver(PG_FUNCTION_ARGS)
 	/* Returns the record as Datum */
 	PG_RETURN_DATUM(HeapTupleGetDatum(heap_form_tuple(tupdesc, values, nulls)));
 }
+
+/* Get the statistics for the replication slots */
+Datum
+pg_stat_get_replication_slots(PG_FUNCTION_ARGS)
+{
+#define PG_STAT_GET_REPLICATION_SLOT_CLOS 5
+	ReturnSetInfo *rsinfo = (ReturnSetInfo *) fcinfo->resultinfo;
+	TupleDesc	tupdesc;
+	Tuplestorestate *tupstore;
+	MemoryContext per_query_ctx;
+	MemoryContext oldcontext;
+	PgStat_ReplSlotStats *slotstats;
+	int			nstats;
+	int			i;
+
+	/* check to see if caller supports us returning a tuplestore */
+	if (rsinfo == NULL || !IsA(rsinfo, ReturnSetInfo))
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				 errmsg("set-valued function called in context that cannot accept a set")));
+	if (!(rsinfo->allowedModes & SFRM_Materialize))
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				 errmsg("materialize mode required, but it is not allowed in this context")));
+
+	/* Build a tuple descriptor for our result type */
+	if (get_call_result_type(fcinfo, NULL, &tupdesc) != TYPEFUNC_COMPOSITE)
+		elog(ERROR, "return type must be a row type");
+
+	per_query_ctx = rsinfo->econtext->ecxt_per_query_memory;
+	oldcontext = MemoryContextSwitchTo(per_query_ctx);
+
+	tupstore = tuplestore_begin_heap(true, false, work_mem);
+	rsinfo->returnMode = SFRM_Materialize;
+	rsinfo->setResult = tupstore;
+	rsinfo->setDesc = tupdesc;
+
+	MemoryContextSwitchTo(oldcontext);
+
+	slotstats = pgstat_fetch_replslot(&nstats);
+	for (i = 0; i < nstats; i++)
+	{
+		Datum		values[PG_STAT_GET_REPLICATION_SLOT_CLOS];
+		bool		nulls[PG_STAT_GET_REPLICATION_SLOT_CLOS];
+		PgStat_ReplSlotStats *s = &(slotstats[i]);
+
+		MemSet(values, 0, sizeof(values));
+		MemSet(nulls, 0, sizeof(nulls));
+
+		values[0] = PointerGetDatum(cstring_to_text(s->slotname));
+		values[1] = Int64GetDatum(s->spill_txns);
+		values[2] = Int64GetDatum(s->spill_count);
+		values[3] = Int64GetDatum(s->spill_bytes);
+
+		if (s->stat_reset_timestamp == 0)
+			nulls[4] = true;
+		else
+			values[4] = TimestampTzGetDatum(s->stat_reset_timestamp);
+
+		tuplestore_putvalues(tupstore, tupdesc, values, nulls);
+	}
+
+	tuplestore_donestoring(tupstore);
+
+	return (Datum) 0;
+}