Re: SGA sizing OenVMS

Michael S. Abbey wrote:
>
> Anyone got any comments about sizing the SGA at greater than 40
> megabytes per instance on an Alpha 8400???
>
> Michael

Be carefull Michael, we run SGA from 100 Mb to 1 Gb and ORACLE has a very hard time managing that much memory (over around 600 Mb). However, on DEC there is a specific version (VLDB) that can support very large SGA which effectively buffer entire Gb's of data.

The most problematic area can be the shared pool. With a very large shared pool there can be latch contention problems when referencing objects (library objects, parsed SQL, ...) In version 7.3 this has been somewhat improved.

The rule of thumb is make your SGA (buffer size) big enough to get your hit ratio around 80% but not above 90% (yeah I know higher seems better but if you have over 1000 users on a system like we have it will kill the server), and get your library cache hits fairly high. If you don't know how to monitor these check out our utilities at http://dbghome.computek.net or refer to the Server Admin Manual.

Hope this helps,
Marc

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|| Marc Marchioli
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