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Re: How is statement level read consistency implemented?

From: Thomas Kellerer <spam_eater(at)gmx(dot)net>
To: pgsql-general(at)postgresql(dot)org
Subject: Re: How is statement level read consistency implemented?
Date: 2008-04-22 13:06:54
Message-ID: fuknte$cmb$1@ger.gmane.org (view raw or flat)
Thread:
Lists: pgsql-general
Roberts, Jon, 22.04.2008 14:56:
>> As far as I can tell (from the PDF and your quote) Postgres uses a
> very
>> similar concept as Oracle. .
>> Each transaction has a uniqe number and each tuple contains the
>> information for which transaction number it is visible.
> 
> Oracle moves the old row(s) to the rollback segment instead of putting a
> new row in the table as PostgreSQL does.  The new value goes right in
> place of the old row and it adds a pointer to the rollback segment.

> A commit removes the pointer and a rollback forces the db to move the
> old row from the rollback segment back in place of the row updated.
> Oracle's rollback segment can be tuned so that retains data up to a
> certain age and then it is flushed.  If rollback is too small, you can
> get a "snapshot too old" error.

Thanks, this was exactly the answer I was looking for!


Cheers
Thomas


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