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Replace the BufMgrLock with separate locks on the lookup hashtable and

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the freelist, plus per-buffer spinlocks that protect access to individual
shared buffer headers.  This requires abandoning a global freelist (since
the freelist is a global contention point), which shoots down ARC and 2Q
as well as plain LRU management.  Adopt a clock sweep algorithm instead.
Preliminary results show substantial improvement in multi-backend situations.
This commit is contained in:
Tom Lane
2005-03-04 20:21:07 +00:00
parent 5592a6cf46
commit 5d5087363d
18 changed files with 1410 additions and 1932 deletions
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107
doc/src/sgml/runtime.sgml
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@ -1,5 +1,5 @@
<!--
$PostgreSQL: pgsql/doc/src/sgml/runtime.sgml,v 1.306 2005/03/02 19:58:54 tgl Exp $
$PostgreSQL: pgsql/doc/src/sgml/runtime.sgml,v 1.307 2005/03/04 20:21:05 tgl Exp $
-->
<chapter Id="runtime">
@ -1379,9 +1379,7 @@ SET ENABLE_SEQSCAN TO OFF;
Specifies the delay between activity rounds for the
background writer. In each round the writer issues writes
for some number of dirty buffers (controllable by the
following parameters). The selected buffers will always be
the least recently used ones among the currently dirty
buffers. It then sleeps for <varname>bgwriter_delay</>
following parameters). It then sleeps for <varname>bgwriter_delay</>
milliseconds, and repeats. The default value is 200. Note
that on many systems, the effective resolution of sleep
delays is 10 milliseconds; setting <varname>bgwriter_delay</>
@ -1393,32 +1391,77 @@ SET ENABLE_SEQSCAN TO OFF;
</listitem>
</varlistentry>
<varlistentry id="guc-bgwriter-percent" xreflabel="bgwriter_percent">
<term><varname>bgwriter_percent</varname> (<type>integer</type>)</term>
<varlistentry id="guc-bgwriter-lru-percent" xreflabel="bgwriter_lru_percent">
<term><varname>bgwriter_lru_percent</varname> (<type>floating point</type>)</term>
<indexterm>
<primary><varname>bgwriter_percent</> configuration parameter</primary>
<primary><varname>bgwriter_lru_percent</> configuration parameter</primary>
</indexterm>
<listitem>
<para>
In each round, no more than this percentage of the currently
dirty buffers will be written (rounding up any fraction to
the next whole number of buffers). The default value is
1. This option can only be set at server start or in the
To reduce the probability that server processes will need to issue
their own writes, the background writer tries to write buffers that
are likely to be recycled soon. In each round, it examines up to
<varname>bgwriter_lru_percent</> of the buffers that are nearest to
being recycled, and writes any that are dirty.
The default value is 1.0 (this is a percentage of the total number
of shared buffers).
This option can only be set at server start or in the
<filename>postgresql.conf</filename> file.
</para>
</listitem>
</varlistentry>
<varlistentry id="guc-bgwriter-maxpages" xreflabel="bgwriter_maxpages">
<term><varname>bgwriter_maxpages</varname> (<type>integer</type>)</term>
<varlistentry id="guc-bgwriter-lru-maxpages" xreflabel="bgwriter_lru_maxpages">
<term><varname>bgwriter_lru_maxpages</varname> (<type>integer</type>)</term>
<indexterm>
<primary><varname>bgwriter_maxpages</> configuration parameter</primary>
<primary><varname>bgwriter_lru_maxpages</> configuration parameter</primary>
</indexterm>
<listitem>
<para>
In each round, no more than this many dirty buffers will be
written. The default value is 100. This option can only be
set at server start or in the
In each round, no more than this many buffers will be written
as a result of scanning soon-to-be-recycled buffers.
The default value is 5.
This option can only be set at server start or in the
<filename>postgresql.conf</filename> file.
</para>
</listitem>
</varlistentry>
<varlistentry id="guc-bgwriter-all-percent" xreflabel="bgwriter_all_percent">
<term><varname>bgwriter_all_percent</varname> (<type>floating point</type>)</term>
<indexterm>
<primary><varname>bgwriter_all_percent</> configuration parameter</primary>
</indexterm>
<listitem>
<para>
To reduce the amount of work that will be needed at checkpoint time,
the background writer also does a circular scan through the entire
buffer pool, writing buffers that are found to be dirty.
In each round, it examines up to
<varname>bgwriter_all_percent</> of the buffers for this purpose.
The default value is 0.333 (this is a percentage of the total number
of shared buffers). With the default <varname>bgwriter_delay</>
setting, this will allow the entire shared buffer pool to be scanned
about once per minute.
This option can only be set at server start or in the
<filename>postgresql.conf</filename> file.
</para>
</listitem>
</varlistentry>
<varlistentry id="guc-bgwriter-all-maxpages" xreflabel="bgwriter_all_maxpages">
<term><varname>bgwriter_all_maxpages</varname> (<type>integer</type>)</term>
<indexterm>
<primary><varname>bgwriter_all_maxpages</> configuration parameter</primary>
</indexterm>
<listitem>
<para>
In each round, no more than this many buffers will be written
as a result of the scan of the entire buffer pool. (If this
limit is reached, the scan stops, and resumes at the next buffer
during the next round.)
The default value is 5.
This option can only be set at server start or in the
<filename>postgresql.conf</filename> file.
</para>
</listitem>
@ -1426,13 +1469,19 @@ SET ENABLE_SEQSCAN TO OFF;
</variablelist>
<para>
Smaller values of <varname>bgwriter_percent</varname> and
<varname>bgwriter_maxpages</varname> reduce the extra I/O load
Smaller values of <varname>bgwriter_all_percent</varname> and
<varname>bgwriter_all_maxpages</varname> reduce the extra I/O load
caused by the background writer, but leave more work to be done
at checkpoint time. To reduce load spikes at checkpoints,
increase the values. To disable background writing entirely,
set <varname>bgwriter_percent</varname> and/or
<varname>bgwriter_maxpages</varname> to zero.
increase these two values.
Similarly, smaller values of <varname>bgwriter_lru_percent</varname> and
<varname>bgwriter_lru_maxpages</varname> reduce the extra I/O load
caused by the background writer, but make it more likely that server
processes will have to issue writes for themselves, delaying interactive
queries.
To disable background writing entirely,
set both <varname>maxpages</varname> values and/or both
<varname>percent</varname> values to zero.
</para>
</sect3>
@ -3866,20 +3915,6 @@ plruby.bar = true # generates error, unknown class name
</listitem>
</varlistentry>
<varlistentry id="guc-debug-shared-buffers" xreflabel="debug_shared_buffers">
<term><varname>debug_shared_buffers</varname> (<type>integer</type>)</term>
<indexterm>
<primary><varname>debug_shared_buffers</> configuration parameter</primary>
</indexterm>
<listitem>
<para>
Number of seconds between ARC reports.
If set greater than zero, emit ARC statistics to the log every so many
seconds. Zero (the default) disables reporting.
</para>
</listitem>
</varlistentry>
<varlistentry id="guc-pre-auth-delay" xreflabel="pre_auth_delay">
<term><varname>pre_auth_delay</varname> (<type>integer</type>)</term>
<indexterm>