From: | Qingqing Zhou <zhouqq(at)cs(dot)toronto(dot)edu> |
---|---|
To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | Simon Riggs <simon(at)2ndquadrant(dot)com>, pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: gprof SELECT COUNT(*) results |
Date: | 2005-11-25 05:58:23 |
Message-ID: | Pine.LNX.4.58.0511250044520.14187@eon.cs |
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Lists: | pgsql-hackers |
On Thu, 24 Nov 2005, Tom Lane wrote:
>
> I don't see those costing nearly as much as your results show
> ... perhaps there's something platform-specific at work?
> What I see, down to the 1% level, is
>
I can see your computer is really slow, so my theory is that since it is
easy to hold a running-slowly horse than a fast one, so my spinlock on a
2.4G modern machine should takes relatively longer time to get effective.
Just kidding. I am not sure what's happened, but in previous email there
is a program I wrote to test the spinlock performance. In my machine, the
profiling results matches the single spinlock test.
>
> The only other objection I can think of is that if there are any broken
> tuples on a page, this approach would likely make it impossible to fetch
> any of the non-broken ones :-(
>
What do you mean by "broken tuple"? An data corrupted tuple? So you mean
if scan operator find a broken tuple on a page, then it will abort the
operation without returning any other good tuples? I think this is
acceptable.
Regards,
Qingqing
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