Don't exaggerate the number of temporary blocks read.

robertmhaas · robertmhaas · commit ee4673ac071f · 2017-10-31T14:56:09.000+05:30
A read that returns zero bytes (or an error) should not increment the number of temporary blocks read. Thomas Munro Discussion: http://postgr.es/m/CAEepm=21xgihg=WaG+O5MFotEZfN6kFETpfw+RkSnEqNQqGn2Q@mail.gmail.com
diff --git a/src/backend/storage/file/buffile.c b/src/backend/storage/file/buffile.c
@@ -264,7 +264,8 @@ BufFileLoadBuffer(BufFile *file)
 	file->offsets[file->curFile] += file->nbytes;
 	/* we choose not to advance curOffset here */
 
-	pgBufferUsage.temp_blks_read++;
+	if (file->nbytes > 0)
+		pgBufferUsage.temp_blks_read++;
 }
 
 /*

Original file line number	Diff line number	Diff line change
`@@ -264,7 +264,8 @@ BufFileLoadBuffer(BufFile *file)`
`264`	`264`	`file->offsets[file->curFile] += file->nbytes;`
`265`	`265`	`/* we choose not to advance curOffset here */`
`266`	`266`
`267`		`- pgBufferUsage.temp_blks_read++;`
	`267`	`+ if (file->nbytes > 0)`
	`268`	`+ pgBufferUsage.temp_blks_read++;`
`268`	`269`	`}`
`269`	`270`
`270`	`271`	`/*`