| From: | Marko Kreen <markokr(at)gmail(dot)com> |
|---|---|
| To: | Simon Riggs <simon(at)2ndquadrant(dot)com> |
| Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>, Erik Rijkers <er(at)xs4all(dot)nl>, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: testing HS/SR - 1 vs 2 performance |
| Date: | 2010-04-23 17:16:09 |
| Message-ID: | s2je51f66da1004231016pc823d9b6yc18a76b32bb3c70e@mail.gmail.com |
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| Lists: | pgsql-hackers |
On 4/18/10, Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:
> On Sat, 2010-04-17 at 16:48 -0400, Tom Lane wrote:
> > There are some places where we suppose that a *single* write into shared
> > memory can safely be done without a lock, if we're not too concerned
> > about how soon other transactions will see the effects. But what you
> > are proposing here requires more than one related write.
> >
> > I've been burnt by this myself:
> > http://archives.postgresql.org/pgsql-committers/2008-06/msg00228.php
>
>
> W O W - thank you for sharing.
>
> What I'm not clear on is why you've used a spinlock everywhere when only
> weak-memory thang CPUs are a problem. Why not have a weak-memory-protect
> macro that does does nada when the hardware already protects us? (i.e. a
> spinlock only for the hardware that needs it).
Um, you have been burned by exactly this on x86 also:
http://archives.postgresql.org/pgsql-hackers/2009-03/msg01265.php
--
marko
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