ALS and delayed commit

We currently use ALS on one of our heavily hit dbs to reduce log
contention.  Now that delayed commit is available for consideration,
would it make sense to add delayed commit on the db along with ALS?
Is that a bad mix or is that reasonable?

Thanks,
Bob
0
Robert
11/16/2010 8:13:59 PM
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On 16-Nov-2010 21:13, Robert Densmore wrote:
> We currently use ALS on one of our heavily hit dbs to reduce log
> contention.  Now that delayed commit is available for consideration,
> would it make sense to add delayed commit on the db along with ALS?
> Is that a bad mix or is that reasonable?
>
> Thanks,
> Bob

Delayed commit applies at the semantics of a commit (i.e. do not wait 
for the write of the last log page to complete) whereas ALS aims at 
alleviating log semaphore contention (flush ULCs to syslogs more 
efficiently). Since they aim at different aspects, they might work in 
combination, at least theoretically. However, I'm guessing this 
combination may not  have been expected. That doens't mean it couldn't 
work, but if you'd run into issues, it would not be a complete surprise 
for me.
Anyway, it depends what type of log contention you're looking at -- disk 
writes or semaphore contention?

Keep in mind that delayed commit may result in losing the last few 
committed transactions, should ASE be shut down abruptly.

HTH,

Rob V.
-----------------------------------------------------------------
Rob Verschoor

Certified Sybase Professional DBA for ASE 15.0/12.5/12.0/11.5/11.0
and Replication Server 15.0.1/12.5 // TeamSybase

Author of Sybase books (order online at www.sypron.nl/shop):
"Tips, Tricks&  Recipes for Sybase ASE" (ASE 15 edition)
"The Complete Sybase ASE Quick Reference Guide"
"The Complete Sybase Replication Server Quick Reference Guide"

rob@NO.SPAM.sypron.nl | www.sypron.nl  | Twitter: @rob_verschoor
Sypron B.V., The Netherlands  |  Chamber of Commerce 27138666
-----------------------------------------------------------------

0
Rob
11/17/2010 10:06:00 AM
On 17 Nov 2010 02:06:00 -0800, "Rob V [ Sybase ]"
<robv@DO.NOT.SPAM.sypron.nl.REMOVE.THIS.DECOY> wrote:

>On 16-Nov-2010 21:13, Robert Densmore wrote:
>> We currently use ALS on one of our heavily hit dbs to reduce log
>> contention.  Now that delayed commit is available for consideration,
>> would it make sense to add delayed commit on the db along with ALS?
>> Is that a bad mix or is that reasonable?
>>
>> Thanks,
>> Bob
>
>Delayed commit applies at the semantics of a commit (i.e. do not wait 
>for the write of the last log page to complete) whereas ALS aims at 
>alleviating log semaphore contention (flush ULCs to syslogs more 
>efficiently). Since they aim at different aspects, they might work in 
>combination, at least theoretically. However, I'm guessing this 
>combination may not  have been expected. That doens't mean it couldn't 
>work, but if you'd run into issues, it would not be a complete surprise 
>for me.
>Anyway, it depends what type of log contention you're looking at -- disk 
>writes or semaphore contention?
>
>Keep in mind that delayed commit may result in losing the last few 
>committed transactions, should ASE be shut down abruptly.
>
>HTH,
>
>Rob V.
>-----------------------------------------------------------------
>Rob Verschoor
>
>Certified Sybase Professional DBA for ASE 15.0/12.5/12.0/11.5/11.0
>and Replication Server 15.0.1/12.5 // TeamSybase
>
>Author of Sybase books (order online at www.sypron.nl/shop):
>"Tips, Tricks&  Recipes for Sybase ASE" (ASE 15 edition)
>"The Complete Sybase ASE Quick Reference Guide"
>"The Complete Sybase Replication Server Quick Reference Guide"
>
>rob@NO.SPAM.sypron.nl | www.sypron.nl  | Twitter: @rob_verschoor
>Sypron B.V., The Netherlands  |  Chamber of Commerce 27138666
>-----------------------------------------------------------------
Thanks.

We have mainly log semaphore contention, but since this db is more of
a working storage db to support the app, recoverability is not a
concern.  So, thought delayed commit would be of benefit also, since
there are very high transactions.  We can't turn off ALS, the system
can't function under a heavy load without it.

Bob
0
Robert
11/17/2010 5:02:26 PM
Reply:

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