From: | Mark Kirkwood <markir(at)paradise(dot)net(dot)nz> |
---|---|
To: | Simon Riggs <simon(at)2ndquadrant(dot)com> |
Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Heikki Linnakangas <heikki(at)enterprisedb(dot)com>, pgsql-patches(at)postgresql(dot)org |
Subject: | Re: scan_recycle_buffers |
Date: | 2007-03-10 10:26:25 |
Message-ID: | 45F287D1.1070305@paradise.net.nz |
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Lists: | pgsql-hackers pgsql-patches |
Simon Riggs wrote:
> On Sat, 2007-03-10 at 07:59 +0000, Simon Riggs wrote:
>> On Fri, 2007-03-09 at 18:05 -0500, Tom Lane wrote:
>>> "Simon Riggs" <simon(at)2ndquadrant(dot)com> writes:
>>>> On Fri, 2007-03-09 at 16:45 -0500, Tom Lane wrote:
>>>>> We do that anyway; but certainly Simon's patch ought not be injecting
>>>>> an additional one.
>>>> It should be possible to pass that down from the planner to the
>>>> executor, in certain cases.
>>> Huh? See HeapScanDesc->rs_nblocks.
>> Many thanks.
>
> New patch enclosed, implementation as you've requested.
>
> Not ready to apply yet, but good for testing.
>
A quick test using the setup for "Buffer cache is not scan resistant"
thread:
Firstly vanilla 8.3 from 20070310:
Shared Buffers Elapsed vmstat IO rate
-------------- ------- --------------
400MB 101 s 122 MB/s
128KB 79 s 155 MB/s [1]
Now apply cycle scan v2:
Shared Buffers Scan_recycle_buffers Elapsed vmstat IO rate
-------------- -------------------- ------- -------------
400MB 0 101 s 122 MB/s
400MB 8 78 s 155 MB/s
400MB 16 77 s 155 MB/s
400MB 32 78 s 155 MB/s
400MB 64 82 s 148 MB/s
400MB 128 93 s 128 MB/s
Certainly seems to have the desired effect!
Cheers
Mark
[1] I'm not seeing 166 MB/s like previous 8.2.3 data, however 8.3 PGDATA
is located further toward the end of the disk array - which I suspect is
limiting the IO rate a little.
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