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Re: oracle - mysql comparison

From: VC <boston103_at_hotmail.com>
Date: Wed, 14 Jul 2004 23:00:11 GMT
Message-ID: <%ViJc.91742$XM6.50454@attbi_s53>


Pls. see below:

"Alex Filonov" <afilonov_at_yahoo.com> wrote in message news:336da121.0407141111.67a9ab79_at_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).
>

Ah, that's what you mean. In this narrow sense, yes, you are right. A more correct way would be to say that Oracle implements a variety of multiversion concurrency control with 'read consistency' being just a part of the mechanism.

DB2 and MSSQL naturally do not have this kind of 'read consistency' (in a narrow sense) since they implement an entirely different concurrency model which prevent neither from producing fully consistent results, read or otherwise, in a proper isolation mode/level.

VC Received on Wed Jul 14 2004 - 18:00:11 CDT

Original text of this message

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