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Re: Re: Snapshot too old during stress test... how to avoid

From: Thomas Day <tday6_at_csc.com>
Date: Thu, 05 Jun 2003 06:04:57 -0800
Message-ID: <F001.005AAE24.20030605060457@fatcity.com>

With optimal, the rollback segment shrinks back to its optimal size as soon as the update, insert, or delete transaction is committed. However, there may be a long running query that is using that rollback segment for a consistent view of the database. If the rollback segment shrinks, the query cannot find the data that it needs. This results in a snapshot too old error.

                                                                                                                                       
                      <rgaffuri                                                                                                        
                      @cox.net>                To:      Multiple recipients of list ORACLE-L <ORACLE-L_at_fatcity.com>                    
                      Sent by: root            cc:                                                                                     
                                               Subject: Re: Re: Snapshot too old during stress test... how to avoid                    
                                                                                                                                       
                      06/05/2003 08:31                                                                                                 
                      AM                                                                                                               
                      Please respond                                                                                                   
                      to ORACLE-L                                                                                                      
                                                                                                                                       
                                                                                                                                       




why would removing optimal setting help with snapshot too old?

what I dont understand is that each of my DML transactions are independent of each other. They query and perform DML on different tables. None of them overlap. The only time they overlap is when they hit the data dictionary for some brief queries.
>
> From: Tim Gorman <tim_at_sagelogix.com>
> Date: 2003/06/05 Thu AM 03:25:36 EDT
> To: Multiple recipients of list ORACLE-L <ORACLE-L_at_fatcity.com>
> Subject: Re: Snapshot too old during stress test... how to avoid
>
> Speaking of this trick with a txn in each RBS, I've got a shell script on
my
> website (http://www.evdbt.com/tools.htm) that does just that. It is
named
> "prevent1555.sh" which uses a stored procedure created by a SQL script
named
> "prevent1555_ddl.sql"...
>
> As Jared mentioned, it is kind of a last resort, but it works...
>
>
>
>
> on 6/4/03 4:05 PM, Jared.Still_at_radisys.com at Jared.Still_at_radisys.com
wrote:
>
> > .. and if it still doesn't work, use the trick of putting a transaction
> > in
> > each of the rollback segments while the system is otherwise quiesced,
> > and *do not* commit or rollback the transactions.
> >
> > This forces the rollbacks to extend if necessary, they will never wrap
> > back to the first extent ( actually the second) as long as those
> > transactions
> > are not committed.
> >
> > It just uses a lot of disk space. Disk is cheap, right? :)
> >
> > Consider offlining all your production RBS and creating temporary ones
> > that you can easily drop later.
> >
> > I've used it with SAP client copies, which will not run to completion
> > without
> > doing this, at least on our system.
> >
> > Jared
> >
> >
> >
> >
> >
> > Kirtikumar Deshpande <kirtikumar_deshpande_at_yahoo.com>
> > Sent by: root_at_fatcity.com
> > 06/04/2003 09:45 AM
> > Please respond to ORACLE-L
> >
> >
> > To: Multiple recipients of list ORACLE-L
<ORACLE-L_at_fatcity.com>
> > cc:
> > Subject: Re: Snapshot too old during stress test... how to
avoid
> >
> >
> > Try removing optimal setting, and shrinking RBS to the min extents (or
> > even below) before running
> > your tests.
> >
> > - Kirti
> >
> >
> > --- Garry Gillies <g.gillies_at_weir.co.uk> wrote:
> >> From memory (of a course attended looong ago),
> >> Oracle recommends one rollback segment for every
> >> three to four users.
> >> Four rollback segments between thirty six processes
> >> does seem a little mean.
> >>
> >> Garry
> >>
> >>
> >>
> >>
> >>
> >> <rgaffuri_at_cox.net>
> >> Sent by: root_at_fatcity.com
> >> 04/06/03 13:59
> >> Please respond to ORACLE-L
> >>
> >>
> >> To: Multiple recipients of list ORACLE-L
> > <ORACLE-L_at_fatcity.com>
> >> cc:
> >> Subject: Snapshot too old during stress test... how to
> > avoid
> >>
> >>
> >> Im testing worst case scenarios right now. So Im doing batch
> >> updates,inserts,deletes and 'create table as' from a staging
tablespace
> > of
> >> approximately 5GBs to a master tablespace of approximately 11GBs.
> >>
> >> Ive got my job queue processes set to 36 and Im running 36 at a time
in
> >> the background in order to gather statistics and timing under worst
case
> >
> >> scenarios.
> >>
> >> Im in 8.1.7.3 and I have increased the size of my RBS tablespace to
11GB
> >
> >> for this test. I have 4 standard RBS with optimal size set to 1GB. Why
> >> would I get a snapshot too old? I would think that 11GBs of rollback
> > would
> >> be big enough. Would increasing the number of Rollback segments avoid
> > this
> >> even though I have the same amount of space in the tablespace?
> >>
> >> In reality Im going to seriallize the process to avoid this and to
> > improve
> >> performance, however, I want to stress the system.
> >>
> >> any advice?
> >>
> >> --
> >> Please see the official ORACLE-L FAQ: http://www.orafaq.net
> >> --
> >> Author: <rgaffuri_at_cox.net
> >> INET: rgaffuri_at_cox.net
> >>
> >
> >
> >
> > __________________________________
> > Do you Yahoo!?
> > Yahoo! Calendar - Free online calendar with sync to Outlook(TM).
> > http://calendar.yahoo.com
>
> --
> Please see the official ORACLE-L FAQ: http://www.orafaq.net
> --
> Author: Tim Gorman
> INET: tim_at_sagelogix.com
>
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--
Please see the official ORACLE-L FAQ: http://www.orafaq.net
--
Author: <rgaffuri_at_cox.net
  INET: rgaffuri_at_cox.net

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-- 
Please see the official ORACLE-L FAQ: http://www.orafaq.net
-- 
Author: Thomas Day
  INET: tday6_at_csc.com

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Received on Thu Jun 05 2003 - 09:04:57 CDT

Original text of this message

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