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RE: RE: oracle or mssql

From: Jenner Mike <>
Date: Thu, 31 Oct 2002 06:03:30 -0800
Message-ID: <>

But this default mssql behaviour is the performance 'gotcha' where readers block writers and writers block readers isn't it?


-----Original Message-----
Sent: 31 October 2002 09:12
To: Multiple recipients of list ORACLE-L

'Dirty reads' in SQL Server means that you can view records that have not been committed. This is implemented by setting the TRANSACTION ISOLATION LEVEL to READ UNCOMMITTED.

This is not default behaviour in SQL Server, the default TIL is READ COMMITTED (for very good reason). I can think of very few situations where you would want to see uncommitted records.

Dirty blocks in SQL Server/Oracle are the same thing ie. a block/page in cache that has been changed but not flushed to disk.


-----Original Message-----
Sent: 30 October 2002 18:43
To: Multiple recipients of list ORACLE-L

It sounds like he is saying that, once an "insert, update or delete" statement has been issued (without a following commit), then the records acted upon are now considered "dirty" - i.e. needing writing to disk.

this is, of course, NOT what Oracle considers a dirty block.

I agree with you, Jared!

Tom Mercadante
Oracle Certified Professional

-----Original Message-----
Sent: Wednesday, October 30, 2002 1:21 PM To: Multiple recipients of list ORACLE-L

At least one of us has the incorrect understanding of 'dirty' reads, or I am taking you too literally, or something.

What are you really saying?

Oracle does not allow dirty reads.

All queries are consistent to a point in time, the beginning of a transaction, whether implicit (select) or explicit ( start transaction ).

SQL Server and Sybase do not guarantee this.

The 'dirty' reads you are speaking of sound more to me like sloppy programming.

Is that what you're referring to?


"Yechiel Adar" <>
Sent by:
 10/30/2002 08:54 AM
 Please respond to ORACLE-L  

        To:     Multiple recipients of list ORACLE-L <>
        Subject:        Re: RE: oracle or mssql

I would like to point out that what you call "dirty reads" are mostly the correct reads. Oracle method IS the dirty read.

I am sure that your users does at least 1000 commits to every rollback. So when oracle gives you the data it already knows that this data is wrong. If you do the query again a minute later you will get new results that were available when you did the original query but were committed later. So you get a 1000/1 chance to get incorrect data.

The "dirty read" method, on the other hand, gives you the current values, believing that they will be committed in a moment. So you get 1/1000 chance
to get wrong data.

Which odds will you bet on?

Yechiel Adar
----- Original Message -----
To: Multiple recipients of list ORACLE-L <> Sent: Tuesday, October 29, 2002 2:18 PM

I'm always keen to refresh on database comparisons so thanks for everyone's pointers.

I'm surprised Oracle doesn't make more of an issue about their locking and concurrency methods (i.e. redo/rollback/undo).

MSSQL seems to deal with it in two ways: Default: readers and writers prevent writers from accessing data until they
are finished with it!
Other method: no control, you just get dirty reads!

Anyone got anything to add to this? Or am I wrong?

-----Original Message-----
Sent: 24 October 2002 17:29
To: Multiple recipients of list ORACLE-L

As I said, use mssql ONLY if your boss is willing to be strapped into a MicroSlop only platform. If he's even remotely thinking of using a different OS
then you can't use mssql.

Dick Goulet

____________________Reply Separator____________________
Date:       10/23/2002 11:48 PM

everybody who responded to my basic question : thanks


professional : use oracle enterprise edition semi professional : use oracle standard edition / mssql enterprise edition in all other cases mssql standard edition

> -----Oorspronkelijk bericht-----
> Van: Mohammad Rafiq []
> Verzonden: woensdag 23 oktober 2002 20:51
> Aan: Multiple recipients of list ORACLE-L
> Onderwerp: RE: oracle or mssql


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Author: Jenner Mike

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Received on Thu Oct 31 2002 - 08:03:30 CST

Original text of this message