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, 29 insertions, 0 deletions

diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index 0f6af952f93..3346df32d3b 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -32,6 +32,7 @@
 #include "access/xlog_internal.h"
 #include "fmgr.h"
 #include "miscadmin.h"
+#include "pgstat.h"
 #include "replication/decode.h"
 #include "replication/logical.h"
 #include "replication/origin.h"
@@ -1460,3 +1461,31 @@ ResetLogicalStreamingState(void)
 	CheckXidAlive = InvalidTransactionId;
 	bsysscan = false;
 }
+
+/*
+ * Report stats for a slot.
+ */
+void
+UpdateDecodingStats(LogicalDecodingContext *ctx)
+{
+	ReorderBuffer *rb = ctx->reorder;
+
+	/*
+	 * Nothing to do if we haven't spilled anything since the last time the
+	 * stats has been sent.
+	 */
+	if (rb->spillBytes <= 0)
+		return;
+
+	elog(DEBUG2, "UpdateSpillStats: updating stats %p %lld %lld %lld",
+		 rb,
+		 (long long) rb->spillTxns,
+		 (long long) rb->spillCount,
+		 (long long) rb->spillBytes);
+
+	pgstat_report_replslot(NameStr(ctx->slot->data.name),
+						   rb->spillTxns, rb->spillCount, rb->spillBytes);
+	rb->spillTxns = 0;
+	rb->spillCount = 0;
+	rb->spillBytes = 0;
+}