Re: SYBASE DBA TO ORACLE DBA

Casey Claiborne <mskc_at_io.com> wrote in article
> I currently have been trained in performance tuning for
> SYBASE system 11; however, I am wondering
> if there are significant or small differences between the
> administration of an Oracle database vs. a SYBASE database - i.e.
 

There are significant architectural differences between the two products. Sybase uses an internal log for both current and complete transactions, which gets dumped to an external file periodically. Oracle has two seperate structures, ROLLBACK SEGMENTS for 'undo' and REDO LOG for completed transactions. The REDO LOG gets written to an external file from its internal buffer as each transaction completes. Moreover, the external redo log file can be multiplexed and automatically archived. Also, Oracle permits row-level locking, while Sybase only locks at the page level.

In terms of managing a production instance, these differences can be significant. For example. transaction managment is affected dramatically. Rollback segments permit 'versioning' of the database, so that readers are never blocked. Sybase, on the other hand, blocks readers to prevent inconsistent views. With Oracle, you have to make sure your ROLLBACK SEGMENTS are large enough to accomodate the largest transactions. Can get a bit tricky.

Also, at least with older versions of Sybase, incomplete transactions (left open for many hours) caused by client sessions that got disconnected or simply started and then ignored by users (in all-day meetings, etc.) don't permit the internal transaction log to be completely cleared. This problem doesn't exist in Oracle, since only completed transactions hit the REDO LOG. Redo and undo are on seperate structures, that is.

And, stored procedures in Sybase are able to return result sets. This feature is new to Oracle and most client products don't support it. Oracle SQL, however, can contain stored functions, which permit SQL to make use of return values. Powerful feature. Of course, the procedural languages T-SQL and PL/SQL are completely different. PL/SQL is somewhat object-oriented.

There are other significant differences, too, but these pop into mind as major and obvious. You really ought to read the Oracle Concepts manual and a good book, either by Oracle Press or O'Reilly. Kevin Loney's DBA Handbook is excellent.

Roger Received on Tue Mar 04 1997 - 00:00:00 CET