localbuf: Introduce FlushLocalBuffer()

Previously we had two paths implementing writing out temporary table
buffers. For shared buffers, the logic for that is centralized in
FlushBuffer(). Introduce FlushLocalBuffer() to do the same for local buffers.

Besides being a nice cleanup on its own, it also makes an upcoming change
slightly easier.

Reviewed-by: Melanie Plageman <melanieplageman@gmail.com>
Discussion: https://postgr.es/m/CAAKRu_b9anbWzEs5AAF9WCvcEVmgz-1AkHSQ-CLLy-p7WHzvFw@mail.gmail.com

src/backend/storage/buffer/bufmgr.c

@@ -4453,7 +4453,6 @@ FlushRelationBuffers(Relation rel)
 		for (i = 0; i < NLocBuffer; i++)
 		{
 			uint32		buf_state;
-			instr_time	io_start;
 
 			bufHdr = GetLocalBufferDescriptor(i);
 			if (BufTagMatchesRelFileLocator(&bufHdr->tag, &rel->rd_locator) &&
@@ -4461,9 +4460,6 @@ FlushRelationBuffers(Relation rel)
 				 (BM_VALID | BM_DIRTY)) == (BM_VALID | BM_DIRTY))
 			{
 				ErrorContextCallback errcallback;
-				Page		localpage;
-
-				localpage = (char *) LocalBufHdrGetBlock(bufHdr);
 
 				/* Setup error traceback support for ereport() */
 				errcallback.callback = local_buffer_write_error_callback;
@@ -4471,23 +4467,7 @@ FlushRelationBuffers(Relation rel)
 				errcallback.previous = error_context_stack;
 				error_context_stack = &errcallback;
 
-				PageSetChecksumInplace(localpage, bufHdr->tag.blockNum);
-
-				io_start = pgstat_prepare_io_time(track_io_timing);
-
-				smgrwrite(srel,
-						  BufTagGetForkNum(&bufHdr->tag),
-						  bufHdr->tag.blockNum,
-						  localpage,
-						  false);
-
-				pgstat_count_io_op_time(IOOBJECT_TEMP_RELATION,
-										IOCONTEXT_NORMAL, IOOP_WRITE,
-										io_start, 1, BLCKSZ);
-
-				TerminateLocalBufferIO(bufHdr, true, 0);
-
-				pgBufferUsage.local_blks_written++;
+				FlushLocalBuffer(bufHdr, srel);
 
 				/* Pop the error context stack */
 				error_context_stack = errcallback.previous;

src/backend/storage/buffer/localbuf.c

@@ -174,6 +174,41 @@ LocalBufferAlloc(SMgrRelation smgr, ForkNumber forkNum, BlockNumber blockNum,
 	return bufHdr;
 }
 
+/*
+ * Like FlushBuffer(), just for local buffers.
+ */
+void
+FlushLocalBuffer(BufferDesc *bufHdr, SMgrRelation reln)
+{
+	instr_time	io_start;
+	Page		localpage = (char *) LocalBufHdrGetBlock(bufHdr);
+
+	/* Find smgr relation for buffer */
+	if (reln == NULL)
+		reln = smgropen(BufTagGetRelFileLocator(&bufHdr->tag),
+						MyProcNumber);
+
+	PageSetChecksumInplace(localpage, bufHdr->tag.blockNum);
+
+	io_start = pgstat_prepare_io_time(track_io_timing);
+
+	/* And write... */
+	smgrwrite(reln,
+			  BufTagGetForkNum(&bufHdr->tag),
+			  bufHdr->tag.blockNum,
+			  localpage,
+			  false);
+
+	/* Temporary table I/O does not use Buffer Access Strategies */
+	pgstat_count_io_op_time(IOOBJECT_TEMP_RELATION, IOCONTEXT_NORMAL,
+							IOOP_WRITE, io_start, 1, BLCKSZ);
+
+	/* Mark not-dirty */
+	TerminateLocalBufferIO(bufHdr, true, 0);
+
+	pgBufferUsage.local_blks_written++;
+}
+
 static Buffer
 GetLocalVictimBuffer(void)
 {
@@ -234,34 +269,7 @@ GetLocalVictimBuffer(void)
 	 * the case, write it out before reusing it!
 	 */
 	if (pg_atomic_read_u32(&bufHdr->state) & BM_DIRTY)
-	{
-		instr_time	io_start;
-		SMgrRelation oreln;
-		Page		localpage = (char *) LocalBufHdrGetBlock(bufHdr);
-
-		/* Find smgr relation for buffer */
-		oreln = smgropen(BufTagGetRelFileLocator(&bufHdr->tag), MyProcNumber);
-
-		PageSetChecksumInplace(localpage, bufHdr->tag.blockNum);
-
-		io_start = pgstat_prepare_io_time(track_io_timing);
-
-		/* And write... */
-		smgrwrite(oreln,
-				  BufTagGetForkNum(&bufHdr->tag),
-				  bufHdr->tag.blockNum,
-				  localpage,
-				  false);
-
-		/* Temporary table I/O does not use Buffer Access Strategies */
-		pgstat_count_io_op_time(IOOBJECT_TEMP_RELATION, IOCONTEXT_NORMAL,
-								IOOP_WRITE, io_start, 1, BLCKSZ);
-
-		/* Mark not-dirty now in case we error out below */
-		TerminateLocalBufferIO(bufHdr, true, 0);
-
-		pgBufferUsage.local_blks_written++;
-	}
+		FlushLocalBuffer(bufHdr, NULL);
 
 	/*
 	 * Remove the victim buffer from the hashtable and mark as invalid.

src/include/storage/buf_internals.h

@@ -473,6 +473,7 @@ extern BlockNumber ExtendBufferedRelLocal(BufferManagerRelation bmr,
 extern void MarkLocalBufferDirty(Buffer buffer);
 extern void TerminateLocalBufferIO(BufferDesc *bufHdr, bool clear_dirty,
 								   uint32 set_flag_bits);
+extern void FlushLocalBuffer(BufferDesc *bufHdr, SMgrRelation reln);
 extern void DropRelationLocalBuffers(RelFileLocator rlocator,
 									 ForkNumber forkNum,
 									 BlockNumber firstDelBlock);