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Re: oracle - mysql comparison

From: Alex Filonov <afilonov_at_yahoo.com>
Date: 15 Jul 2004 08:33:59 -0700
Message-ID: <336da121.0407150733.5db6de1@posting.google.com>


"VC" <boston103_at_hotmail.com> wrote in message news:<%ViJc.91742$XM6.50454_at_attbi_s53>...
> Pls. see below:
>
> "Alex Filonov" <afilonov_at_yahoo.com> wrote in message
> news:336da121.0407141111.67a9ab79_at_posting.google.com...
> > "VC" <boston103_at_hotmail.com> wrote in message
> news:<KbZIc.81643$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.
>

According to some information M$ is going to implement read-only consistency (Oracle style) in the next version. As for correct concurrency model, I remember one project, when data warehouse was build using MSSQL, everything was almost OK, management was pleased immensely. Until they started running reports. When management found out that reports practically stopped online work, mood changed.

>
> VC
Received on Thu Jul 15 2004 - 10:33:59 CDT

Original text of this message

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