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Implement COMMIT_SIBLINGS parameter to allow pre-commit delay to occur

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only if at least N other backends currently have open transactions.  This
is not a great deal of intelligence about whether a delay might be
profitable ... but it beats no intelligence at all.  Note that the default
COMMIT_DELAY is still zero --- this new code does nothing unless that
setting is changed.
Also, mark ENABLEFSYNC as a system-wide setting.  It's no longer safe to
allow that to be set per-backend, since we may be relying on some other
backend's fsync to have synced the WAL log.
This commit is contained in:
Tom Lane
2001-02-26 00:50:08 +00:00
parent 60774e8210
commit 9c9936587c
10 changed files with 94 additions and 31 deletions
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13
doc/src/sgml/wal.sgml
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@ -1,4 +1,4 @@
<!-- $Header: /cvsroot/pgsql/doc/src/sgml/wal.sgml,v 1.2 2001/02/18 04:50:43 tgl Exp $ -->
<!-- $Header: /cvsroot/pgsql/doc/src/sgml/wal.sgml,v 1.3 2001/02/26 00:50:07 tgl Exp $ -->
<chapter id="wal">
<title>Write-Ahead Logging (<acronym>WAL</acronym>)</title>
@ -295,10 +295,13 @@
record to the log with <function>LogInsert</function> but before
performing a <function>LogFlush</function>. This delay allows other
backends to add their commit records to the log so as to have all
of them flushed with a single log sync. Unfortunately, this
mechanism is not fully implemented at release 7.1, so there is at
present usually no benefit to be gained from increasing this parameter
above its default value of zero.
of them flushed with a single log sync. No sleep will occur if fsync
is not enabled or if fewer than <varname>COMMIT_SIBLINGS</varname>
other backends are not currently in active transactions; this avoids
sleeping when it's unlikely that any other backend will commit soon.
Note that on most platforms, the resolution of a sleep request is
ten milliseconds, so that any nonzero <varname>COMMIT_DELAY</varname>
setting between 1 and 10000 microseconds will have the same effect.
</para>
</sect1>
</chapter>