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  Oracle Tips by Burleson

Monitoring and Tuning the Shared Pool

Let me begin this subsection by stating that the default values for the shared pool size initialization parameters are almost always too small by at least a factor of 4. Unless your database is limited to the basic scott/tiger type schema, and your overall physical data size is less than a couple of hundred megabytes, even the  “large” parameters are far too small. Which parameters control the size of the shared pool? Essentially, only one: SHARED_POOL_SIZE. The other shared-pool parameters control how the variable-space areas in the shared pool are parsed out, but not overall shared pool size. In Oracle8, a new area, the large pool, controlled by the LARGE_POOL_SIZE parameter, is also present. The large pool shares latch structures with the shared pool, so proper sizing of the large pool is critical to help maintain shared pool health.

Generally speaking, I suggest you start at a shared-pool size of 40 megabytes and move up from there. The large pool size will depend on the number of concurrent users, number of multithreaded server servers and dispatchers and the sort requirements for the application.      

What should you monitor to determine if the shared pool is too small? For this, you need to wade into the data dictionary tables, specifically the V$SGASTAT and V$SQLAREA views. Source 13.2 is a report that shows how much of the shared pool is in use at any given time the script is run.

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