Re: Rollback Segment: Read Consistency Errors

On Sun, 12 Aug 2001 12:52:14 +0800, Dino Hsu <dino1_at_ms1.hinet.net> wrote:

>Dear all,
>
>Quoting from a book:
>"Troubleshooting Rollback Segment Problems:
>Read Consistency Errors:
>Recall that rollback segments allow transaction-level read consistency
>for all statements running on the database. A long-running query in
>one session that starts before a change on that data is committed by
>another session will see the data as it existed pre-commit. If Oracle
>cannot provide a read-consistent view of data, the following error
>will ensue:
>
>ORA-01555 - snapshot too old (rollback segment too small)
>
>The solution to the problem is to re-create the rollback segments with
>a higher minimum number of extents, larger extents, or a higher
>optimal rollback segment size. You cannot simply increase maxextents
>to resolve this problem."
>
>If the maxextents is bigger, the max rollback segment size is bigger,
>so it takes longer to get this snapshot too old error. Does my
>rationale hold? Thanks in advance.
>
>Dino
>

No.

Creating lots of extents through a transaction would just make more extents ready to be snatched by other transactions as changes are committed which again will increase the probability of ORA-01555.

Larger extents, not more extents, is the most effective mean against ORA-01555...IMHO, of course.

Regards,
Kenneth Koenraadt
Systems Consultant
Oracle DBA
plovmand@<no-spam>hotmail.com Received on Sun Aug 12 2001 - 04:53:47 CDT