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Add new buffers_backend_fsync field to pg_stat_bgwriter.

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This new field counts the number of times that a backend which writes a
buffer out to the OS must also fsync() it.  This happens when the
bgwriter fsync request queue is full, and is generally detrimental to
performance, so it's good to know when it's happening.  Along the way,
log a new message at level DEBUG1 whenever we fail to hand off an fsync,
so that the problem can also be seen in examination of log files
(if the logging level is cranked up high enough).

Greg Smith, with minor tweaks by me.
This commit is contained in:
Robert Haas
2010-11-15 12:42:59 -05:00
parent 8d70ed84ba
commit 3134d8863e
10 changed files with 34 additions and 8 deletions
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doc/src/sgml/monitoring.sgml
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@@ -264,8 +264,10 @@ postgres: <replaceable>user</> <replaceable>database</> <replaceable>host</> <re
and the number of times the background writer stopped a cleaning scan
because it had written too many buffers. Also includes
statistics about the shared buffer pool, including buffers written
by backends (that is, not by the background writer) and total buffers
allocated.
by backends (that is, not by the background writer), how many times
those backends had to execute their own fsync calls (normally the
background writer handles those even when the backend does its own
write), and total buffers allocated.
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