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Don Burleson Blog 






  Understanding db_keep_cache_size

Oracle Database Tips by Donald BurlesonApril 19, 2015

My understanding of db_keep_cache_size is limited. I created a db_keep_cache_size with a size of 10g, with the goal of placing a NAME table and indexes in this cache. This table is highly searched, and especially joined to.  It also has quite a few updates, a few deletes, about 12 million rows and almost 20 indexes.

Could placing this name table and the most common indexes into this cache help? Would it have any negative effects? Due to my limited understanding of db_keep_cache_size, I'm unsure of doing this and can't replicate the high volume access on our test system.

Here is a script that automates keep pool assignment.

According to Oracle documentation, ?A good candidate for a segment to put into the KEEP pool is a segment that is smaller than 10% of the size of the DEFAULT buffer pool and has incurred at least 1% of the total I/Os in the system?.

More concisely, a small table that is in high demand is a good candidate for KEEP caching.

Another method for identifying tables and indexes for the KEEP pool examines the current blocks in the data buffer. For this query, the rules are simple. Any object that has more than 80% of its data blocks in the data buffer should probably be fully-cached.

Make sure to increase db_keep_cache_size afterwards:

If you like Oracle tuning, you might enjoy my book "Oracle Tuning: The Definitive Reference", with 950 pages of tuning tips and scripts. 

You can buy it direct from the publisher for 30%-off and get instant access to the code depot of Oracle tuning scripts.


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