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rate. I have heard that there can be contention for the database buffer cache. How do I detect database buffer cache contention and minimize or eliminate it?<p><B>Technique</B><p>There are two potential causes of database buffer cache contention. The first occurs when user processes have to skip an increasing number of dirty buffers to find a clean one. This situation generates waits. The second kind of contention is latch contention. A latch is a serialization mechanism that protects the structures residing in the SGA; Oracle uses many different types of latches.<p>User processes need a particular latch, the cache buffer chains latch, when they look for free buffers in the database buffer cache. A second user requesting this latch must wait for the current holder of the latch to release it. In this way, the cache buffer chains latch serializes requests on behalf of user processes that need to scan the database buffer cache.<p>The UTLESTAT report contains statistics that may help you identify both of these potential contention problems. Listings 15.15 and 15.16 show excerpts from the report, which highlights database buffer wait statistics and database buffer latch contention, respectively.<p>Listing 15.15 An excerpt from the UTLESTAT report showing buffer cache wait statistics<p><code><b>SQLDBA> Rem The total is the total value of the statistic between the time<p>SQLDBA> Rem bstat was run and the time estat was run. Note that the estat<p>SQLDBA> Rem script logs on as 搃nternal
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