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Automatic RAM memory management in Oracle

As we have noted, a serious problem in Oracle8i was the requirement that all dedicated connections use a one-size-fits-all sort_area_size. Oracle now has the option of running automatic PGA memory management. Oracle has introduced a new init.ora parameter called pga_aggregate_target. When the pga_aggregate_target parameter is set and you are using dedicated Oracle connections, Oracle will ignore all of the PGA parameters in the init.ora file, including sort_area_size and sort_area_retained_size. Oracle recommends that the value of pga_aggregate_target be set to the amount of remaining memory (less a 20% overhead for other UNIX tasks) on the UNIX server after the instance has been started.

Once the pga_aggregate_target has been set, Oracle will automatically manage PGA memory allocation, based upon the individual needs of each Oracle connection. Oracle also allows the pga_aggregate_target parameter to be modified at the instance level with the alter system command, thereby allowing the DBA to dynamically adjust the total RAM region available to Oracle.

Oracle also introduces a new parameter called workarea_size_policy. When this parameter is set to automatic, all Oracle connections will benefit from the shared PGA memory. When workarea_size_policy is set to manual, connections will allocate memory according to the values for the sort_area_size parameter. Under this automatic mode, Oracle tries to maximize the number of work areas that are using optimal memory and uses one-pass memory for the others.


The above is an excerpt from the "Oracle UNIX Administration Handbook" by Oracle press, authored by Donald K. Burleson.

 

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