Keep Buffer Cache Not Large Enough

What happens if I pin a table/index in the keep buffer cache but the keep buffer cache is not large enough? How does oracle determine what to initially put into the keep buffer cache and what to leave out?

>
Well, I got some of them directly from the Oracle docs:
“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”.
But the rules you quoted in your previous post were - not the rule you got from Oracle !
- Use the KEEP pool if the object consumes more than 10% of the total size of the data buffer.
- Use the KEEP pool if more than 50% of the objects blocks already resides in the data buffer, according to an x$bh query.
But I agree, I use my own set of decision rules, which vary by system.
There is no "one size fits all" set of rules . . . . . But you just said you use the rules you got from Oracle in the previous post that:
The placement criteria for tables and indexes into the KEEP buffer are straightforward:
Please make up your mind.
By the way, your script hot_buffers.sql from the page you mentioned above has a few errors in it. The join between x$bh and dba_objects should be on data_object_id, not on object_id; and by joining dba_objects to dba_segments on object_name = segment_name you've introduced a lot of errors relating to index-organised tables, partitioned tables, clusters etc.
Please see Metalink note: 135223.1. Although it's got a couple of things in it that appeared back in the days of 8i (the original document was written in 1998 I believe) it has a better analysis of the issues.
Jonathan Lewis
http://jonathanlewis.wordpress.com
http://www.jlcomp.demon.co.uk

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