Re: Rollback Segments

Darek

> "Snapshot too old .." means that you have a long running query or read-only
> transaction which uses data being changed by other transactions while it's
> running. Oracle uses rollback segments to retrieve older values (to give you
> consistent view of data). After transaction commits its rollback entries may
> be used for this purpose until another transaction need a place in this
> rollback segment.
> So, let's say you have a long-running query which - among others - uses
> data from table X. While it is running another transaction changes some data
> in table X and commits. The older values (before change) are in the rollback
> segment and query can still reach it. But after some time another
> transaction can reuse this place in rollback segment. Then, if your query
> (which is still running) needs to get the previous values of some rows in X
> you will get "Snapshot too old ..." message.
> The simplest solution is to lock in exclusive mode all the tables your
> query uses. But I know it can be unacceptable because it would stop all
> transactions that want to modify these tables. So, probably, the best thing
> you can start with is to make your rollback segments generally biger. The
> values you gave seem very small to me. I'd suggest for example 16 rollback
> segments like this:
> initial 1M next 1M minextents 10 optimal 10M
> in a 200M tablespace (divide it by something if you can not afford so much).
>
> -> my advice: always use maxextents or optimal or fill the tablespace
> tightly with segments!
>
> Darek
>

  Thank you very much for your help and the other people who answered my question. I decided to use 10 rollback segments with initial 512K next 512K minextents 10 optimal 5120K and it seems to work fine now.

  Carlos

-----== Posted via Deja News, The Leader in Internet Discussion ==----- http://www.dejanews.com/rg_mkgrp.xp Create Your Own Free Member Forum Received on Sat Aug 22 1998 - 08:54:24 CDT