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Re: oracle - mysql comparison

From: Alex Filonov <afilonov_at_yahoo.com>
Date: 14 Jul 2004 12:11:13 -0700
Message-ID: <336da121.0407141111.67a9ab79@posting.google.com>


"VC" <boston103_at_hotmail.com> wrote in message news:<KbZIc.81643$Oq2.30187_at_attbi_s52>...
> Hello,
>
> Please see in-line:
>
> "Alex Filonov" <afilonov_at_yahoo.com> wrote in message
> news:336da121.0407131327.363b8e5a_at_posting.google.com...
> > As for consistency (I suppose you mean read-only), it's implemented in
> > ProgreSQL, another Open Source DB engine. BTW, other commercial RMBDS
> > (DB2, MSSQL) don't have read-only consistency and sell pretty well at
> that.
>
> Please define 'read-only consistency' and elaborate a bit on why DB2 and
> MSSQL don't have it.
>

Read-only consistency is defined well enough in Oracle Concepts document. In short, it means that result of any query reflects commited data in the tables as of time when the query was submitted, without locking any objects in the database (readers don't block writers, writers don't block readers).

DB2 and MSSQL can do either dirty read (including uncommited changes) or consistent read with lock (read commited). To my knowledge, only PostgreSQL and Interbase have read-only consistency in Oracle definition.

As for why... I don't work (and never did) for either IBM or M$, so I don't have an answer to this question.

> Thanks.
>
> VC
Received on Wed Jul 14 2004 - 14:11:13 CDT

Original text of this message

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