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  Oracle Tips by Burleson

Tuning the Three Pools

In Oracle8i, the classic method of tuning the shared pool is not available, so we must examine alternative methods to achieve the same ends. This involves looking at what Oracle has provided for tuning the pools. A script, catperf.sql, offers several views for tuning the Oracle buffer pools.

These views are:

  • V$BUFFER_POOL. Provides static information on pool configuration.

  • V$BUFFER_POOL_STATISTICS. Provides pool-related statistics.

  • V$DBWR_WRITE_HISTOGRAM. Provides summary information on DBWR write activities.

  • V$DBWR_WRITE_LOG. Provides write information for each buffer area.

Of these four views, V$BUFFER_POOL_STATISTICS seems the most useful for tuning the buffer pool. It contains statistics such as buffer_busy_waits, free_buffer_inspected, dirty_buffers_inspected, and physical write-related data.
If a buffer pool shows excessive numbers of dirty_buffers_inspected, and high amounts of buffer_busy_waits, then it probably needs to be increased in size.
In Oracle, the V$DB_CACHE_ADVISE view is available for tuning the buffer areas, which is described in the next subsection.

When configuring LRU latches and DBWR processes, remember that the latches are assigned to the pools sequentially and to the DBRW processes in round-robin fashion. The number of LRU processes should be equal to or a multiple of the value of DBWR processes to ensure that the DBRW load is balanced across the processes.

This is an excerpt by Mike Ault’s book “Oracle Administration & Management” .  If you want more current Oracle tips by Mike Ault, check out his new book “Mike Ault’s Oracle Internals Monitoring & Tuning Scripts” or Ault’s Oracle Scripts Download.


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