Oracle-L: RE: Transaction Isolation levels in Oracle!

From: DENNIS WILLIAMS <DWILLIAMS_at_LIFETOUCH.COM>
Date: Tue, 27 May 2003 08:44:55 -0800
Message-ID: <F001.005A35E7.20030527084455@fatcity.com>

Has anyone found a practical use for these isolation levels? My impression is they are mainly offered to:

1. Meet ANSI requirements.
2. Help code port unchanged from other systems.
3. Lure the unwary into using them and causing performance issues in their

system.
My experience has been that Oracle handles transactions extremely well and trying to "help" it only causes degradation.

Dennis Williams
DBA, 80%OCP, 100% DBA
Lifetouch, Inc.
dwilliams_at_lifetouch.com

-----Original Message-----
Sent: Tuesday, May 27, 2003 11:20 AM
To: Multiple recipients of list ORACLE-L

Oracle (I do NOT mean Rdb) supports 2 levels of isolation:

Read committed, which means, you can get non-repaetable reads (the data within a certain row has been changed (upate) due to another transaction's commit, while you're still in the context of the same transaction you were in when you first read the data) and phantom reads (which means the number of rows between reads from within your transaction context changed due to insert / delete activities done by another transaction (which was committed)). Dirty reads (where you would see uncommitted changes done by other transactions) are not allowed.

Serializable, which means, that neither dirty reads, nor non-repeatable reads nor phantom reads occur.

Important: Dirty reads are never possible in Oracle (AFAIK).

Hope that's correct,
Stefan

-----Ursprüngliche Nachricht-----
Von: Murali Menon [mailto:mjgnmenon_at_yahoo.com] Gesendet: Dienstag, 27. Mai 2003 16:45
An: Multiple recipients of list ORACLE-L Betreff: Transaction Isolation levels in Oracle!

Most databases today provide various levels of transaction isolation. READ WRITE, READ ONLY etc and based on the application requirements one or the other is used.

for example, in Oracle Rdb, (the other database from Oracle), we could start a transaction with READ ONLY and the Rdb engine would avoid creation of before and after images etc.

What are the various types of isolation levels in Oracle? I have read about isolation level called READ COMMITTED, is this same as READ ONLY?

Regards,

Menon

Do you Yahoo!?
The <http://us.rd.yahoo.com/search/mailsig/*http://search.yahoo.com> New Yahoo! Search - Faster. Easier. Bingo.

--

Please see the official ORACLE-L FAQ: http://www.orafaq.net
--

Author: DENNIS WILLIAMS
INET: DWILLIAMS_at_LIFETOUCH.COM

Fat City Network Services    -- 858-538-5051 http://www.fatcity.com
San Diego, California        -- Mailing list and web hosting services
---------------------------------------------------------------------

To REMOVE yourself from this mailing list, send an E-Mail message to: ListGuru_at_fatcity.com (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB ORACLE-L (or the name of mailing list you want to be removed from). You may also send the HELP command for other information (like subscribing). Received on Tue May 27 2003 - 11:44:55 CDT