Re: A transaction question

From: David BL <davidbl_at_iinet.net.au>
Date: Wed, 23 Jul 2008 02:11:53 -0700 (PDT)
Message-ID: <534a7084-2850-4c5d-bb22-6942d2acc836@x35g2000hsb.googlegroups.com>


On Jul 23, 3:42 pm, Christoph Rupp <cruppst..._at_gmail.com> wrote:
> Hi,
>
> i have a question about two parallel transactions which insert the
> same key.
>
> Assume that key A does not yet exist.
>
> T1 Begin
> T2 Begin
> T1 Insert A
> T2 Insert A
> T1 Commit
> T2 Commit
>
> My guess is: "T2 Insert A" is a conflict with the previous insert of
> T1. But i also think that in a MVCC database the conflict can only be
> resolved when T2 is committed. What happens then? Does the commit
> fail, or is A silently overwritten? Or is the typical behaviour in
> this case implementation-specific?
>
> Thanks for your answers,
> Christoph

I think MVCC is normally (only) aimed at allowing for better concurrency between readers and writers (and not amongst writers) and therefore is inapplicable in this example. ie the transactions would necessarily be serialised. Received on Wed Jul 23 2008 - 04:11:53 CDT

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