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

Daniel W. Fink Fri, 06 Jun 2003 01:12:45 -0700

Are you hitting ORA-1555 because of a fetch across commit?

[EMAIL PROTECTED] wrote:

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 <[EMAIL PROTECTED]>
Date: 2003/06/05 Thu AM 03:25:36 EDT
To: Multiple recipients of list ORACLE-L <[EMAIL PROTECTED]>


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, [EMAIL PROTECTED] at [EMAIL PROTECTED] 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 <[EMAIL PROTECTED]>
Sent by: [EMAIL PROTECTED]
06/04/2003 09:45 AM
Please respond to ORACLE-L


      To:     Multiple recipients of list ORACLE-L <[EMAIL PROTECTED]>
      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 <[EMAIL PROTECTED]> 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 





<[EMAIL PROTECTED]>
Sent by: [EMAIL PROTECTED]
04/06/03 13:59
Please respond to ORACLE-L


        To:     Multiple recipients of list ORACLE-L

<[EMAIL PROTECTED]>

        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? 

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