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

From: Stefan Jahnke <Stefan.Jahnke_at_bov.de>
Date: Tue, 27 May 2003 08:19:56 -0800
Message-ID: <F001.005A354E.20030527081956@fatcity.com>

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

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Author: Stefan Jahnke
INET: Stefan.Jahnke_at_bov.de

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