Tweak BgBufferSync() so that a persistent write error on a dirty buffer

tglsfdc · tglsfdc · commit 6eac4e69cf34 · 2005-08-02T20:52:08.000Z
doesn't block the bgwriter from making progress writing out other buffers.
This was a hard problem in the context of the ARC/2Q design, but it's
trivial in the context of clock sweep ... just advance the sweep counter
before we try to write not after.
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
@@ -37,7 +37,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/postmaster/bgwriter.c,v 1.17 2005/06/30 00:00:51 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/postmaster/bgwriter.c,v 1.18 2005/08/02 20:52:08 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -256,8 +256,7 @@ BackgroundWriterMain(void)
 		/*
 		 * Sleep at least 1 second after any error.  A write error is
 		 * likely to be repeated, and we don't want to be filling the
-		 * error logs as fast as we can.  (XXX think about ways to make
-		 * progress when the LRU dirty buffer cannot be written...)
+		 * error logs as fast as we can.
 		 */
 		pg_usleep(1000000L);
 	}
diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/storage/buffer/bufmgr.c,v 1.189 2005/05/19 21:35:46 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/storage/buffer/bufmgr.c,v 1.190 2005/08/02 20:52:08 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -903,6 +903,11 @@ BgBufferSync(void)
 	/*
 	 * This loop runs over all buffers, including pinned ones.  The
 	 * starting point advances through the buffer pool on successive calls.
+	 *
+	 * Note that we advance the static counter *before* trying to write.
+	 * This ensures that, if we have a persistent write failure on a dirty
+	 * buffer, we'll still be able to make progress writing other buffers.
+	 * (The bgwriter will catch the error and just call us again later.)
 	 */
 	if (bgwriter_all_percent > 0.0 && bgwriter_all_maxpages > 0)
 	{
@@ -911,12 +916,13 @@ BgBufferSync(void)
 
 		while (num_to_scan-- > 0)
 		{
-			if (SyncOneBuffer(buf_id1, false))
-				num_written++;
 			if (++buf_id1 >= NBuffers)
 				buf_id1 = 0;
-			if (num_written >= bgwriter_all_maxpages)
-				break;
+			if (SyncOneBuffer(buf_id1, false))
+			{
+				if (++num_written >= bgwriter_all_maxpages)
+					break;
+			}
 		}
 	}
 
@@ -934,11 +940,12 @@ BgBufferSync(void)
 		while (num_to_scan-- > 0)
 		{
 			if (SyncOneBuffer(buf_id2, true))
-				num_written++;
+			{
+				if (++num_written >= bgwriter_lru_maxpages)
+					break;
+			}
 			if (++buf_id2 >= NBuffers)
 				buf_id2 = 0;
-			if (num_written >= bgwriter_lru_maxpages)
-				break;
 		}
 	}
 }

Original file line number	Diff line number	Diff line change
`@@ -37,7 +37,7 @@`
`37`	`37`	`*`
`38`	`38`	`*`
`39`	`39`	`* IDENTIFICATION`
`40`		`- * $PostgreSQL: pgsql/src/backend/postmaster/bgwriter.c,v 1.17 2005/06/30 00:00:51 tgl Exp $`
	`40`	`+ * $PostgreSQL: pgsql/src/backend/postmaster/bgwriter.c,v 1.18 2005/08/02 20:52:08 tgl Exp $`
`41`	`41`	`*`
`42`	`42`	`*-------------------------------------------------------------------------`
`43`	`43`	`*/`
`@@ -256,8 +256,7 @@ BackgroundWriterMain(void)`
`256`	`256`	`/*`
`257`	`257`	`* Sleep at least 1 second after any error. A write error is`
`258`	`258`	`* likely to be repeated, and we don't want to be filling the`
`259`		`- * error logs as fast as we can. (XXX think about ways to make`
`260`		`- * progress when the LRU dirty buffer cannot be written...)`
	`259`	`+ * error logs as fast as we can.`
`261`	`260`	`*/`
`262`	`261`	`pg_usleep(1000000L);`
`263`	`262`	`}`
Original file line number	Diff line number	Diff line change
`@@ -8,7 +8,7 @@`
`8`	`8`	`*`
`9`	`9`	`*`
`10`	`10`	`* IDENTIFICATION`
`11`		`- * $PostgreSQL: pgsql/src/backend/storage/buffer/bufmgr.c,v 1.189 2005/05/19 21:35:46 tgl Exp $`
	`11`	`+ * $PostgreSQL: pgsql/src/backend/storage/buffer/bufmgr.c,v 1.190 2005/08/02 20:52:08 tgl Exp $`
`12`	`12`	`*`
`13`	`13`	`*-------------------------------------------------------------------------`
`14`	`14`	`*/`
`@@ -903,6 +903,11 @@ BgBufferSync(void)`
`903`	`903`	`/*`
`904`	`904`	`* This loop runs over all buffers, including pinned ones. The`
`905`	`905`	`* starting point advances through the buffer pool on successive calls.`
	`906`	`+ *`
	`907`	`+ * Note that we advance the static counter before trying to write.`
	`908`	`+ * This ensures that, if we have a persistent write failure on a dirty`
	`909`	`+ * buffer, we'll still be able to make progress writing other buffers.`
	`910`	`+ * (The bgwriter will catch the error and just call us again later.)`
`906`	`911`	`*/`
`907`	`912`	`if (bgwriter_all_percent > 0.0 && bgwriter_all_maxpages > 0)`
`908`	`913`	`{`
`@@ -911,12 +916,13 @@ BgBufferSync(void)`
`911`	`916`
`912`	`917`	`while (num_to_scan-- > 0)`
`913`	`918`	`{`
`914`		`- if (SyncOneBuffer(buf_id1, false))`
`915`		`- num_written++;`
`916`	`919`	`if (++buf_id1 >= NBuffers)`
`917`	`920`	`buf_id1 = 0;`
`918`		`- if (num_written >= bgwriter_all_maxpages)`
`919`		`- break;`
	`921`	`+ if (SyncOneBuffer(buf_id1, false))`
	`922`	`+ {`
	`923`	`+ if (++num_written >= bgwriter_all_maxpages)`
	`924`	`+ break;`
	`925`	`+ }`
`920`	`926`	`}`
`921`	`927`	`}`
`922`	`928`
`@@ -934,11 +940,12 @@ BgBufferSync(void)`
`934`	`940`	`while (num_to_scan-- > 0)`
`935`	`941`	`{`
`936`	`942`	`if (SyncOneBuffer(buf_id2, true))`
`937`		`- num_written++;`
	`943`	`+ {`
	`944`	`+ if (++num_written >= bgwriter_lru_maxpages)`
	`945`	`+ break;`
	`946`	`+ }`
`938`	`947`	`if (++buf_id2 >= NBuffers)`
`939`	`948`	`buf_id2 = 0;`
`940`		`- if (num_written >= bgwriter_lru_maxpages)`
`941`		`- break;`
`942`	`949`	`}`
`943`	`950`	`}`
`944`	`951`	`}`