Re: scan_recycle_buffers

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.