Message-ID: <43049ED2.1080606@arbash-meinel.com>
Date: Thu, 18 Aug 2005 09:44:34 -0500
From: John A Meinel <john@arbash-meinel.com>
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To: Qingqing Zhou <zhouqq@cs.toronto.edu>
Cc: pgsql-performance@postgresql.org
Subject: Re: Performance pb vs SQLServer.
References: <6BCB9D8A16AC4241919521715F4D8BCE6C789C@algol.sollentuna.se>
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Qingqing Zhou wrote:
> "Alvaro Herrera" <alvherre@alvh.no-ip.org> writes
>
>>Interesting; do they use an overwriting storage manager like Oracle, or
>>a non-overwriting one like Postgres?
>>
>
>
> They call this MVCC "RLV(row level versioning)". I think they use rollback
> segment like Oracle (a.k.a "version store" or tempdb in SQL Server).  Some
> details are explained in their white paper:"Database concurrency and row
> level versioning in SQL Server 2005".
>
> Regards,
> Qingqing
>

I found the paper here:
http://www.microsoft.com/technet/prodtechnol/sql/2005/cncrrncy.mspx

And it does sound like they are doing it the Oracle way:

When a record in a table or index is updated, the new record is stamped
with the transaction sequence_number of the transaction that is doing
the update. The previous version of the record is stored in the version
store, and the new record contains a pointer to the old record in the
version store. Old records in the version store may contain pointers to
even older versions. All the old versions of a particular record are
chained in a linked list, and SQL Server may need to follow several
pointers in a list to reach the right version. Version records need to
be kept in the version store only as long as there are there are
operations that might require them.

John
=:->

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