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When to trigger a dynamic reconfiguration

When your scripts detect a condition where a RAM memory region is overstressed, you are faced with a choice about which region will shrink to provide the RAM for the over-stressed area. Table 7-2 below provides the threshold condition for triggering a dynamic memory change.

RAM Area
Over-stressed Condition
Over-allocated Condition
Shared pool
Library cache misses
No misses
Data buffer cache
Hit ratio < 90%
Hit ratio > 95%
PGA aggregate
high multi-pass executions
100% optimal executions

Table 2: Threshold conditions for dynamic RAM re-allocation

In practice, the choice of which area to reduce is size is a choice between the shared pool and the PGA aggregate memory. This is because the shared pool is almost always a small region when compared to the regions for the data buffers and PGA session memory.

The above is an excerpt from the "Oracle UNIX Administration Handbook" by Oracle press, authored by Donald K. Burleson.

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