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set compatibility_mode on

3 posts in Performance and Tuning Last posting was on 2013-02-19 06:48:28.0Z
krishna Posted on 2013-02-14 14:50:13.0Z
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From: Krishna
Newsgroups: sybase.public.ase.performance+tuning
Subject: set compatibility_mode on
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Hi,

We have upgraded one production server from 12.5.4 to 15.5
ESD 4 ON solaris 18 months back. 3 months back we migrated
this server from solaris to Linux (15.5 ESD#4 only).
Recently users are complaining that few procs are running
slow. These procs are using differred compilation. If we
suggest set compatibility_mode on for them, which optimizer
it will use? 12.5.4 or 15.5? Please advice. Thanks in
advance.


Rob V Posted on 2013-02-16 19:50:34.0Z
From: Rob V <rob@sypron.nl>
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On 14-Feb-2013 15:50, Krishna wrote:
> Hi,
>
> We have upgraded one production server from 12.5.4 to 15.5
> ESD 4 ON solaris 18 months back. 3 months back we migrated
> this server from solaris to Linux (15.5 ESD#4 only).
> Recently users are complaining that few procs are running
> slow. These procs are using differred compilation. If we
> suggest set compatibility_mode on for them, which optimizer
> it will use? 12.5.4 or 15.5? Please advice. Thanks in
> advance.
>

With compatibility mode enabled (there is also a server-wide
configuration parameter apart from the session-specific 'set' command),
the best summary is that 12.5 query optimizer and execution engine will
be 'used'. but only for those statements where this is possible. For
example, when using any of the new features in 15.x, that statement is
usually executed with the 15 query optimizer when compatibility mode is
enabled.
When migrating from 12.5 to 15.x and not making any changes to the SQL
code, query plans and query execution should be very similar to ASE 12.5
with compatibility mode enabled. Of course, many of the generic query
processing improvements in ASE 15 will not be used either in this case.

You should read the following whitepaper on comaptibility mode:
http://www.sybase.com/detail?id=1063556

--
HTH,

Rob V.
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Rob Verschoor

Certified Professional DBA for Sybase ASE, IQ, Replication Server

Author of Sybase books (order online at www.sypron.nl/shop):
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"The Complete Sybase IQ Quick Reference Guide"
"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
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krishna Posted on 2013-02-19 06:48:28.0Z
Sender: 4180.51231fe9.1804289383@sybase.com
From: Krishna
Newsgroups: sybase.public.ase.performance+tuning
Subject: Re: set compatibility_mode on
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Date: 18 Feb 2013 22:48:28 -0800
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Hi Rob,

Thank you very much.