RE: Cache a table

Before Oracle 8 and the new touch count algorithm the cache attribute made sense. If a small, frequently used table was read by a full scan, it would have been put at the end of the LRU chain eligible to be aged out immediately, quite possibly by itself if it consisted of more than ~ db_file_multiblock_read_count blocks, i.e. the 2nd or 3rd full scan read would already override the previously read blocks. Marking the table as CACHEd prevented that.

At 01:09 PM 10/21/2003, you wrote:
>I always wondered why Oracle thought this was a useful table attribute.
>
>My gut feeling is that it is an extra that does little.
>
>For example, say we want to keep a code table in memory because it is
>constantly being hit for column verifiction. By definition, if a table is
>constantly being queried, it's segments will be in memory because they never
>age out. That sounds like cacheing to me.
>
>And then I remember a specific piece of Oracle documentation saying that,
>even though we may mark a table to be "cached", it *still* may be aged out
>if memory is needed for other data blocks.
>
>Like I said, sounds a little like "here you have it, and here you don't".
>
>I'm sure that my impression is wrong and someone will correct me. But I
>doubt I will use the "CACHE" option anytime soon.
>
>Tom Mercadante
>Oracle Certified Professional

Wolfgang Breitling
Oracle7, 8, 8i, 9i OCP DBA
Centrex Consulting Corporation
http://www.centrexcc.com

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