Re: Drawbacks to Serializable Mode?

From: Thomas Kyte <tkyte_at_us.oracle.com>
Date: Fri, 26 Feb 1999 15:10:29 GMT
Message-ID: <36dab7ee.6885020@192.86.155.100>

A copy of this was sent to terrysutton_at_usa.net (if that email address didn't require changing) On Thu, 25 Feb 1999 22:33:27 GMT, you wrote:

>We are considering setting a database to Serializable = True to eliminate
>non-repeatable reads.Does anyone have experience with this? What exactly
>are the performance effects? Why shouldn't we do it?--Terry
>
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I would use the transaction level isolation settings available with 7.3.3 and up instead of serializable = true in an init.ora for the following reasons:

• 8 obsoletes this setting in the init.ora, no long supported

The initialization parameter SERIALIZABLE=TRUE is no longer supported in Oracle8 and beyond. The default behavior henceforth is as if SERIALIZABLE was set to FALSE. Use the SET TRANSACTION ISOLATION LEVEL SERIALIZABLE command to achieve similar transaction isolation behavior.

• serializable = true causes a share table lock to be placed whenever you READ a table (not so with serializable transactions using set transaction). This means, if you read a table with serializable=true -- no one can insert/update/delete it until you commit. slightly bad for concurrency.

Thomas Kyte
tkyte_at_us.oracle.com
Oracle Service Industries
Reston, VA USA

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Opinions are mine and do not necessarily reflect those of Oracle Corporation Received on Fri Feb 26 1999 - 09:10:29 CST