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Don Burleson Blog 







 dbms_stats.set_system_stats Tips

Oracle Database Tips by Donald BurlesonMarch 7, 2015

Question:  I need to use the dbms_stats.set_system_stats to change b y system statistics.  How do I invoke the dbms_stats.set_system_stats procedure?

Answer:  An example of using dbms_stats.set_system_stats relates to bug 9842771. This bug leads to wrong values in AUX_STATS$ for sreadtim and mreadtim by factor 1,000 therefore guiding the optimizer sometimes into the totally wrong direction.

The workaround is to overwrite these values manually and divide them by 10,000. To make this change, use the dbms_stats.set_system_stats  procedure. See this MOSC Note:9842771.8 for the above bug for some further information. This issue is fixed in Oracle Database and above.

The following code uses dbms_stats.set_system_stats to change system stats, thereby changing how the optimizer chooses between using an index and performing a full-table scan:

exec dbms_stats.set_system_stats('sreadtim',1000);

exec dbms_stats.set_system_stats('mreadtim',0.01);

exec dbms_stats.set_system_stats('mbrc',512);

exec dbms_stats.set_system_stats('cpuspeed',100);

exec dbms_stats.set_system_stats('maxthr',4000000);

exec dbms_stats.set_system_stats('slavethr',100000);


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