From 6eac4e69cf348fcce13e8d8d63196876bf80d730 Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Tue, 2 Aug 2005 20:52:08 +0000
Subject: [PATCH] Tweak BgBufferSync() so that a persistent write error on a
dirty buffer 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.
---
src/backend/postmaster/bgwriter.c | 5 ++---
src/backend/storage/buffer/bufmgr.c | 23 +++++++++++++++--------
2 files changed, 17 insertions(+), 11 deletions(-)
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index d826a6190de..f4158fc89a5 100644
--- 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
index 1fe681e1aba..4fb16eb6145 100644
--- 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;
}
}
}
--
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