[Fedora-directory-users] Tuning nsslapd-dbcachesize on Solaris

[Rich Megginson]

Added here - 
http://directory.fedora.redhat.com/wiki/Performance_Tuning#Database_Tuning_Considerations

David Boreham wrote:

> George Holbert wrote:
>
>> When tuning FDS on a Solaris machine, I've heard two different 
>> suggestions about nsslapd-dbcachesize:
>> 1. Decrease nsslapd-dbcachesize, and instead rely on Solaris' 
>> built-in filesystem cache which performs better.
>> 2. Tune nsslapd-dbcachesize up to a value that is at least as large 
>> as the size of your backend LDBM database.
>
>
> The filesystem cache doesn't really perform better. (Pages that are
> in the db cache are used directly from process memory. Any page
> that is not resident in the db cache must be fetched from the filesystem,
> incuring a user/kernel transition and a memory copy of the payload.)
> Someone way back ran some tests and convinced themselves that it
> did, and then wrote that doc ;) Actually there was some basis in reality
> until recently we didn't have a 64-bit Solaris version, however the
> filesystem cache was able to use 64-bit address space. So for VLDB
> deployments it was true that the filesystem cache delivered better
> overall use of system memory beyond 2-ishGbytes.
>
> But, the filesystem cache does ok (as is the case on all modern OS'es)
> so if you aren't looking for tip-top performance it's fine to confiure a
> smallish db cache and rely mostly on the filesystem.
>
> One thing to note is that the db cache is mmap'ed, and Solaris does
> some very strange and evil things with mmap'ed files that are not
> in tmpfs filesystems (it will decide all of a sudden to write back
> dirty pages to disk at an amazing rate, to the exclusion of performing
> all other useful work on the box). The solution to this problem is
> documented : put the db home dir in tmpfs (or use sysv memory,
> but that's not officially supported I don't think).
>
>
> -- 
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