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Tempdb

2 posts in General Discussion Last posting was on 2010-09-29 23:10:04.0Z
guest1 Posted on 2010-09-29 21:16:17.0Z
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Subject: Tempdb
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Hi

We have tempdb on SRDF filesystem. We are considering moving
this to non SRDF raw device. Tempdb is bound to its own
cache which is sized 10% of the actual size of the tempdb.
Sysmon does not indicate cache misses, so logical io
requirements appear to be met.

Question is, is it the physical writes that would benefit
from moving off SRDF storage and how can stats proving this
can be derived. MDA data does appear to show how some of
this but I am unsure how to analyse the cache table data

Is there a limitation on how big the tempdb cache can be
sized or adverse impact? i.e can it be sized to match the
size of tempdb database provided someone will get the
requisite memory?


Thanks


Rob V [ Sybase ] Posted on 2010-09-29 23:10:04.0Z
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On 29-Sep-2010 23:16, guest1 wrote:
> Hi
>
> We have tempdb on SRDF filesystem. We are considering moving
> this to non SRDF raw device. Tempdb is bound to its own
> cache which is sized 10% of the actual size of the tempdb.
> Sysmon does not indicate cache misses, so logical io
> requirements appear to be met.
>
> Question is, is it the physical writes that would benefit
> from moving off SRDF storage and how can stats proving this
> can be derived. MDA data does appear to show how some of
> this but I am unsure how to analyse the cache table data
>
> Is there a limitation on how big the tempdb cache can be
> sized or adverse impact? i.e can it be sized to match the
> size of tempdb database provided someone will get the
> requisite memory?
>
>
> Thanks

There is no limit on the size of the cache that tempdb is bound to.
Obviously, making it bigger than tempdb itself is a waste of memory.
When the cache is as big as tempdb itself, nothing will in principle be
written to disk for tempdb.

As for the DB devices for tempdb: it is not a good idea to put tempdb on
a device that is mirrored or otherwise incurs some kind of overhead.
Typically tempdb is put on a filesystem with dsync = false to make it as
fast as possible (though there's more to say about this topics, this is
a good principle).

HTH,

Rob V.
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Rob Verschoor

Certified Sybase Professional DBA for ASE 15.0/12.5/12.0/11.5/11.0
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Author of Sybase books (order online at www.sypron.nl/shop):
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"The Complete Sybase ASE Quick Reference Guide"
"The Complete Sybase Replication Server Quick Reference Guide"

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