Improve IO accounting for temp relation writes

Both pgstat_database and pgBufferUsage count IO timing for reads of temporary
relation blocks into local buffers. However, both failed to count write IO
timing for flushes of dirty local buffers. Fix.

Additionally, FlushRelationBuffers() seems to have omitted counting write
IO (both count and timing) stats for both pgstat_database and
pgBufferUsage. Fix.

Author: Melanie Plageman <melanieplageman@gmail.com>
Reviewed-by: Andres Freund <andres@anarazel.de>
Discussion: https://postgr.es/m/20230321023451.7rzy4kjj2iktrg2r%40awork3.anarazel.de

src/backend/storage/buffer/bufmgr.c

@@ -4062,6 +4062,8 @@ FlushRelationBuffers(Relation rel)
 {
 	int			i;
 	BufferDesc *bufHdr;
+	instr_time	io_start,
+				io_time;
 
 	if (RelationUsesLocalBuffers(rel))
 	{
@@ -4087,6 +4089,11 @@ FlushRelationBuffers(Relation rel)
 
 				PageSetChecksumInplace(localpage, bufHdr->tag.blockNum);
 
+				if (track_io_timing)
+					INSTR_TIME_SET_CURRENT(io_start);
+				else
+					INSTR_TIME_SET_ZERO(io_start);
+
 				smgrwrite(RelationGetSmgr(rel),
 						  BufTagGetForkNum(&bufHdr->tag),
 						  bufHdr->tag.blockNum,
@@ -4098,6 +4105,16 @@ FlushRelationBuffers(Relation rel)
 
 				pgstat_count_io_op(IOOBJECT_TEMP_RELATION, IOCONTEXT_NORMAL, IOOP_WRITE);
 
+				if (track_io_timing)
+				{
+					INSTR_TIME_SET_CURRENT(io_time);
+					INSTR_TIME_SUBTRACT(io_time, io_start);
+					pgstat_count_buffer_write_time(INSTR_TIME_GET_MICROSEC(io_time));
+					INSTR_TIME_ADD(pgBufferUsage.blk_write_time, io_time);
+				}
+
+				pgBufferUsage.local_blks_written++;
+
 				/* Pop the error context stack */
 				error_context_stack = errcallback.previous;
 			}

src/backend/storage/buffer/localbuf.c

@@ -176,6 +176,8 @@ GetLocalVictimBuffer(void)
 	int			trycounter;
 	uint32		buf_state;
 	BufferDesc *bufHdr;
+	instr_time	io_start,
+				io_time;
 
 	ResourceOwnerEnlargeBuffers(CurrentResourceOwner);
 
@@ -239,6 +241,11 @@ GetLocalVictimBuffer(void)
 
 		PageSetChecksumInplace(localpage, bufHdr->tag.blockNum);
 
+		if (track_io_timing)
+			INSTR_TIME_SET_CURRENT(io_start);
+		else
+			INSTR_TIME_SET_ZERO(io_start);
+
 		/* And write... */
 		smgrwrite(oreln,
 				  BufTagGetForkNum(&bufHdr->tag),
@@ -252,6 +259,15 @@ GetLocalVictimBuffer(void)
 
 		/* Temporary table I/O does not use Buffer Access Strategies */
 		pgstat_count_io_op(IOOBJECT_TEMP_RELATION, IOCONTEXT_NORMAL, IOOP_WRITE);
+
+		if (track_io_timing)
+		{
+			INSTR_TIME_SET_CURRENT(io_time);
+			INSTR_TIME_SUBTRACT(io_time, io_start);
+			pgstat_count_buffer_write_time(INSTR_TIME_GET_MICROSEC(io_time));
+			INSTR_TIME_ADD(pgBufferUsage.blk_write_time, io_time);
+		}
+
 		pgBufferUsage.local_blks_written++;
 	}