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, 22 insertions, 0 deletions

diff --git a/src/backend/replication/logical/reorderbuffer.c b/src/backend/replication/logical/reorderbuffer.c
index 1975d629a6e..189641bbf5b 100644
--- a/src/backend/replication/logical/reorderbuffer.c
+++ b/src/backend/replication/logical/reorderbuffer.c
@@ -343,6 +343,10 @@ ReorderBufferAllocate(void)
 	buffer->outbufsize = 0;
 	buffer->size = 0;
 
+	buffer->spillTxns = 0;
+	buffer->spillCount = 0;
+	buffer->spillBytes = 0;
+
 	buffer->current_restart_decoding_lsn = InvalidXLogRecPtr;
 
 	dlist_init(&buffer->toplevel_by_lsn);
@@ -1579,6 +1583,13 @@ ReorderBufferTruncateTXN(ReorderBuffer *rb, ReorderBufferTXN *txn)
 	{
 		ReorderBufferRestoreCleanup(rb, txn);
 		txn->txn_flags &= ~RBTXN_IS_SERIALIZED;
+
+		/*
+		 * We set this flag to indicate if the transaction is ever serialized.
+		 * We need this to accurately update the stats as otherwise the same
+		 * transaction can be counted as serialized multiple times.
+		 */
+		txn->txn_flags |= RBTXN_IS_SERIALIZED_CLEAR;
 	}
 
 	/* also reset the number of entries in the transaction */
@@ -3112,6 +3123,7 @@ ReorderBufferSerializeTXN(ReorderBuffer *rb, ReorderBufferTXN *txn)
 	int			fd = -1;
 	XLogSegNo	curOpenSegNo = 0;
 	Size		spilled = 0;
+	Size		size = txn->size;
 
 	elog(DEBUG2, "spill %u changes in XID %u to disk",
 		 (uint32) txn->nentries_mem, txn->xid);
@@ -3170,6 +3182,16 @@ ReorderBufferSerializeTXN(ReorderBuffer *rb, ReorderBufferTXN *txn)
 		spilled++;
 	}
 
+	/* update the statistics iff we have spilled anything */
+	if (spilled)
+	{
+		rb->spillCount += 1;
+		rb->spillBytes += size;
+
+		/* don't consider already serialized transactions */
+		rb->spillTxns += (rbtxn_is_serialized(txn) || rbtxn_is_serialized_clear(txn)) ? 0 : 1;
+	}
+
 	Assert(spilled == txn->nentries_mem);
 	Assert(dlist_is_empty(&txn->changes));
 	txn->nentries_mem = 0;