Sunday, January 17, 2010

Dataabse hit ratios

Dictionary Cache Hit Ratio

The dictionary hit ratio displays the percentage of memory reads for the data dictionary and other objects.

Query for dictionary hit ratio

SQL>select (1-(sum(getmisses)/sum(gets))) * 100 "Hit Ratio" from v$rowcache

Library Cache Hit Ratio

The library cache hit ratio reveals the percentage of memory reads for actual statements and PL/SQL objects. Note that a high hit ratio is not always good; see Chapter 4 for a detailed explanation.
Query for library hit ratio

select Sum(Pins) / (Sum(Pins) + Sum(Reloads)) * 100 "Hit Ratio"
from V$LibraryCache

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