Re: Rollback Segments

Jerry and Carlos,

        Assigning the large rollback segment to Carlos' long running transaction will not help. He needs to add more rollback segments. The ora-1555 tells you that during your long running transaction, somebody modified a block and committed a change to the block during the time your transaction has been running. Then, another transaction overlaid the old version of the block in the rollback segment. Your transaction tries to get its read consistent view and it's not there anymore.

        Since RBS's are used in round robin fashion, by adding more RBS's, it will take longer for your system to roll around to re-using an RBS, overlaying the version of the block you want. If you can't add more rollback segments, the only other alternative is running the app at truly off-peak time, like when NOBODY else is on the system. ORA-1555's are a result of Oracle's implementation of read-consistency and except for solution 2 (NOBODY), there is no guarantee you will not see an ora-1555.

HTH, Frank         

On Mon, 17 Aug 1998 13:41:45 -0400, Jerry Gitomer <jgitomer_at_ictgroup.com> wrote:

>Hi Carlos,
>
> Adding more rollback segments won't help. There are three alternatives
>(one of which may not apply in your case):
>
> 1. Increase maxextents (I think you are at the limit for NT)
>
> 2. Increase initial and/or next extents from 50K to at least 100K.
>
> 3. Create a very large rollback segment and then assign the big
>transaction to it using the SET TRANSACTION command.
>
> My personal preference is the third alternative since, in most cases,
>only one very large rollback segment is needed and it is, IMHO, more
>desirable to have less disk space tied up.
>
>regards
>
>Jerry
>
>
>
>
>
>calberto_at_my-dejanews.com wrote:
>>
>> Hi all!
>>
>> I'm having problems with rollback segments in Oracle. We, in our company, have
>> an long-running application (about 3 hours) which after 2 hours give us the
>> following message :
>>
>> ORA 01555 - Snapshot too old .....
>>
>> The server currently has 16 rollback segments, which one with the following
>> parameters :
>>
>> INITIAL - 50K
>> NEXT - 50K
>> OPTIMAL - DEFAULT (I suppose Oracle's default is NULL)
>> MINEXTENTS - 2
>> MAXEXTENTS - 121
>>
>> Is the solution increase the NEXT parameter?
>>
>> Beyond this, I have some doubts :
>>
>> 1) I have manually put all these segments online, but when the machine
>> rebooted (for other reasons), Oracle have put some of them offline. Why?
>>
>> 2) Since my OPTIMAL parameter is the default, when Oracle will release the
>> extents of the segments?
>>
>> 3) All these rollback segments are in one tablespace which has 2 datafiles of
>> 20 MB each, but there is only 2 MB free. Is this related with the problem?
>>
>> We have Oracle 7.3 running on NT 4.0.
>>
>> Thank in advanced,
>>
>> Carlos
>>
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>
>--
>Jerry Gitomer ICT Group
>jgitomer_at_ictgroup.com Langhorne PA
>jgitomer_at_yahoo.com Opinions are mine not those of ICT Group
Received on Mon Aug 17 1998 - 13:53:25 CDT