Data Dictionary Cache Hit Ratio (DictHitRatio)

The DictHitRatio parameter reports the percentage of all requests for data dictionary attributes that are resolved from the dictionary cache (also referred to as the row cache).

DictHitRatio is calculated by pulling the values from the database each time the parameter runs a poll cycle, that is, collects data. The values are stored in variables. Each time the parameter polls, the difference between the new value and old value received from the sga_row_cache_gets and sga_row_cache_misses and is scaled for an hour (delta).

Using delta values identifies when the dictionary hit ratio is low or high at a certain polling interval.

If accumulative values were used, it would not reflect what was happening now, but rather reflect the ratio since the database instance was started.
You can make the polling cycle longer, based on your particular needs.

In Oracle8, it is extremely unusual for this cache not to be correctly sized automatically. If it is too small, then the shared pool must be made larger.

Recommendations
If the DictHitRatio value is consistently low, do the following things:

• Increase the init.ora shared_pool_size parameter 2 to reduce implicit reparsing of SQL statements and PL/SQL blocks on execution.
• If needed, increase the init.ora open_cursors parameter to increase the number of cursors permitted for a session.This action takes advantage of additional memory available for shared SQL areas.
• Whenever possible, use stored procedures and identical SQL statements in applications so that they can share a SQL area.

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