IDS Forum

RE: IDS performance

Posted By: david david
Date: Tuesday, 3 August 2004, at 5:56 a.m.

Writing caching is SITUATION SPECIFIC..depends if you

a) write to the same page
i) immediately after the first write - to reduce multiple writes
ii) whilst the page is still in memory (to avoid needing to pull the page into
memory so it can be updated)

b) read from the same page
i) whilst the page is still in memory(to avoid needing to pull the page into
memory so it can be read)

If you are doing one-off writes to the pages and not accessing them again then
caching does not help. Most cases I would recommend at least 5-10Mb of cache
even on low end systems since writse to the same page immediately will become
one write instead of two! Even low end systems I used to work with could flush
1Mb/sec to disk. Larger faster systems e.g. something with 8Gb of memory instead
of 256Mb and EMC arrays with Gb's of cache could probably have more write cache since
they could probably manage to flush more than 1Mb/sec to disk during checkpoints!
Size the write cache based on

a) user response times dictated by checkpoint times - irrelevant in batch only systems
(use different settings during large updates/upgrades when users are not on
the system?)
b) probability that write caching will reduce writes
c) size of the machine

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