Re: Performance question

On Wed, 2 Jul 2003, Tom Lane wrote:

> Jean-Christian Imbeault <jc@mega-bucks.co.jp> writes:
> > I have suggested that their current INSERT INTO t VALUES() be changed to:
>
> > INSERT INTO
> >    T
> > SELECT 'v1', 'v2'
> > WHERE
> >    NOT EXISTS (
> >      SELECT NULL FROM t WHERE pk='v1'
> >    )
>
> That doesn't really buy anything in safety terms: if two backends
> execute this sort of command concurrently, it's perfectly likely
> that both sub-SELECTS will find no row matching 'v1', and so they'll
> both try the INSERT anyway.
>
> IMO the best way to do this (assuming that you have a unique index
> defined on the primary key column) is to just go ahead and try the
> INSERT, but be prepared to roll back your transaction and retry
> if you get a failure.
>
> You might find it useful to read the slides from my talk at last
> year's O'Reilly conference about this and related concurrency
> problems:
> http://conferences.oreillynet.com/cs/os2002/view/e_sess/2681
>

I'd like to see all presentations in one collections. It'd be nice
addition to documentation.


>             regards, tom lane
>
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>

    Regards,
        Oleg
_____________________________________________________________
Oleg Bartunov, sci.researcher, hostmaster of AstroNet,
Sternberg Astronomical Institute, Moscow University (Russia)
Internet: oleg@sai.msu.su, http://www.sai.msu.su/~megera/
phone: +007(095)939-16-83, +007(095)939-23-83