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doc: update effective_io_concurrency for SSDs 

SSDs are no longer exotic, so recommend a default in the hundreds for
them.
This commit is contained in:
Bruce Momjian 2016-06-28 16:09:04 -04:00
parent b78364df18
commit 46eafc8855
1 changed files with 4 additions and 8 deletions
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doc/src/sgml/config.sgml
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@ -1944,20 +1944,16 @@ include_dir 'conf.d'
</para>
<para>
A good starting point for this setting is the number of separate
For magnetic drives, a good starting point for this setting is the
number of separate
drives comprising a RAID 0 stripe or RAID 1 mirror being used for the
database. (For RAID 5 the parity drive should not be counted.)
However, if the database is often busy with multiple queries issued in
concurrent sessions, lower values may be sufficient to keep the disk
array busy. A value higher than needed to keep the disks busy will
only result in extra CPU overhead.
</para>
<para>
For more exotic systems, such as memory-based storage or a RAID array
that is limited by bus bandwidth, the correct value might be the
number of I/O paths available. Some experimentation may be needed
to find the best value.
SSDs and other memory-based storage can often process many
concurrent requests, so the best value might be in the hundreds.
</para>
<para>