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Oracle Metric In Memory Sort Ratio

Oracle Consulting Tips by Burleson


The Oracle docs note: "The In Memory Sort Ratio Oracle metric is the percentage of sorts (from ORDER BY clauses or index building) that are done to disk vs. in-memory.  Disk sorts are done in the TEMP tablespace, which is hundreds of times slower than a RAM sort.  The in-memory sorts are controlled by sort_area_size or by pga_aggregate_target."

At the time a session is established with Oracle, a private sort area is allocated in RAM memory for use by the session for sorting. If the connection is via a dedicated connection a Program Global Area (PGA) is allocated according to the sort_area_size init.ora parameter.

For connections via the multithreaded server, sort space is allocated in the large_pool. Unfortunately, the amount of memory used in sorting must be the same for all sessions, and it is not possible to add additional sort areas for tasks that require large sort operations.

You can reduce in-memory sorts in a number of ways:

This, and many other Oracle performance metrics are discussed in my book "
Oracle Tuning" by Rampant TechPress.  You can buy it directly from the publisher and save 30% at this link:



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Note: This Oracle documentation was created as a support and Oracle training reference for use by our DBA performance tuning consulting professionals.  Feel free to ask questions on our Oracle forum.

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