Hi

But there is something called the touch count algorithm in 8i and above in which you can make modifications to change the LRU performance.

By default Oracle divides the LRU evenly. That is, the hot region(MRU) is composed of 50% of the buffers and the cold region(LRU) is composed of 50% of the buffers. This can be controlled by manipulating the instance parameter, _db_percent_hot_default. Increasing this instance parameter will increase the percentage of buffers in the hot region, that is, buffers above the midpoint.

There are five relevant touch-count related instance parameters that we can use to our advantage.

_db_percent_hot_default. The percentage of block buffers that reside in the hot region. Default 50 (percent).

_db_aging_touch_time. The window of time where a buffer’s touch count can only be incremented by one. Default 3 (seconds).

_db_aging_hot_creiteria. The threshold when a buffer is being considered to be moved to the MRU end of the LRU chain. Default 2 (touch count).

_db_againg_stay_count. Involved with resetting the touch count when a buffer is moved to the MRU end of the LRU chain. Default 0 (touch count).

_db_aging_cool_count. The re-assigned touch count value when a block moves from the hot region into the cold region. Default 1 (touch count).

Not much is available on the above parameters, so u need to experiment urself to find out what each parameter does and how it would affect your performance.

An excellent document on touch count by Craig A. Shallahamer is available on www.orapub.com

Regards
Amar