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Re: testing HS/SR - 1 vs 2 performance

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: (view raw, whole thread or download thread mbox)
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:
>  >
> 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:


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Subject: Re: testing HS/SR - 1 vs 2 performance
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