Re: Disabling rollback. Is it possible?

You cannot disable rollback segments.

Before Image read-consistency functionality is a fundamental and necessary component to any fully relational database. While it's true that Oracle v7.2 will introduce 'operations' that will allow you to turn off logging (UNRECOVERABLE), this will not provide any benefit to your rollback segment problems.

I agree that this area of database management may be one of the most frustrating because it provides you, the DBA with the least control. However, it light of the frequency of your problems, it seems the Rollback Segment strategy you currently have employed is ineffective. It may be due to having too few segments, inadequate segment size(s), default OPTIMAL settings, etc. Scrutinize the Oracle text with regards to this matter and learn of the V$ performance tables which will show you how often your segments are extending and shrinking and how to setr the OPTIMAL size, accordingly. If you're still at a loss, supply the NET with these statistics as well as what your SELECT statement(s) will return in terms of volume. There are many bright people who can use this information in a far more effective manner than if you were to ask to just 'turn off rollback segments' simply because this (turning off rollback segments) will not happen any time soon (my opinion).

I'm not one to endorse stealth-ware, but versions 7.2 and 7.3 Oracle will be attempting to address the needs of the clients having large repositories. Some subtle changes in v7.1 provide for quicker index creates using the 'Parallel' functionality. The method in which extents are trimmed can be frustrating to manage. And while Parallel functionality does exist for Queries, I am not impressed with it's abilities for queries other than a single large table scan. In v7.2 you will be able to recreate tables and indexes with logging turned off, which means if you're in a position where the recreation of these objects is required, the task can be expedited. V7.2 is also suppose to introduce Star-Query (sounds cool). This querying functionality is 'rumored' to provide large queries, particularly those having 3 or more tables within a join condition (or subqueries), much better performance. A few of us are speculating that Oracle's acquirement of DEC's Rdb may be the source for their improvements in the COST optimzer, which up through v7.1 has been dysfunctional. If anyone tells you COST works in v7.1 or before, let me know and I can forward them some EXPLAIN plans that should stifle this hype.  I am particularly sensitive about this issue because Oracle instructors for the DBA-II course will stand before a packed room of students, 50% of which are rookies to the Oracle RDBMS, and the instructors go on and on about how wonderful COST is. Trust me...COST is EXPENSIVE. (Is this perhaps why your queries have become long-standing transactions that eat up your rollback segments?)

I hope what little substance I have provided here has helped in some way. It seems every monday morning I light up my machine and provide someone an uninvited dissertation. This morning you were the victim. Congratulations.

Have a good week.

-D Received on Mon Aug 14 1995 - 00:00:00 CEST