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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.
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@ -1944,20 +1944,16 @@ include_dir 'conf.d'
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</para>
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</para>
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<para>
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<para>
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A good starting point for this setting is the number of separate
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For magnetic drives, a good starting point for this setting is the
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number of separate
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drives comprising a RAID 0 stripe or RAID 1 mirror being used for the
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drives comprising a RAID 0 stripe or RAID 1 mirror being used for the
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database. (For RAID 5 the parity drive should not be counted.)
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database. (For RAID 5 the parity drive should not be counted.)
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However, if the database is often busy with multiple queries issued in
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However, if the database is often busy with multiple queries issued in
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concurrent sessions, lower values may be sufficient to keep the disk
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concurrent sessions, lower values may be sufficient to keep the disk
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array busy. A value higher than needed to keep the disks busy will
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array busy. A value higher than needed to keep the disks busy will
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only result in extra CPU overhead.
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only result in extra CPU overhead.
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</para>
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SSDs and other memory-based storage can often process many
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concurrent requests, so the best value might be in the hundreds.
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<para>
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For more exotic systems, such as memory-based storage or a RAID array
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that is limited by bus bandwidth, the correct value might be the
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number of I/O paths available. Some experimentation may be needed
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to find the best value.
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</para>
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</para>
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<para>
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<para>
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