Because of this,
having a larger buffer cache may not contribute to performance since there isn??™t
much reuse of data blocks occurring.
In addition, not all operations read from the database buffer cache. For example,
large full-table scans are limited to a small number of buffers to avoid adversely
impacting other users by dominating the cache. If your application performs a lot of
table scans, increasing the buffer cache may not help performance because the cache
will not contain the needed data blocks. Parallel table scans completely bypass the
buffer cache and pass rows directly to the requesting user process. As with most performance
issues, your understanding of how your application is actually using your
data is the key that will help guide your database buffer-cache tuning.
The shared pool
The shared pool is used at several points during the execution of every operation that
occurs in an Oracle database. For example, the shared pool is accessed to cache the
178 | Chapter 7: Oracle Performance
SQL sent to the database and for the data dictionary information required to execute
the SQL.
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