2011/5/3 Merlin Moncure <mmoncure@gmail.com>:
> On Tue, May 3, 2011 at 8:55 AM, Cédric Villemain
> <cedric.villemain.debian@gmail.com> wrote:
>> 2011/5/3 Merlin Moncure <mmoncure@gmail.com>:
>>>
>>> no it will not, or at least there is no guarantee it will be. the
>>> only way to reset the buffers in that sense is to restart the database
>>> (and even then they might not be read from disk, because they could
>>> sit in the o/s cache). to force a read from the drive you'd have to
>>> reboot the server, or at least shut it down and use a lot of memory
>>> for some other purpose.
>>
>> with linux, you can : "echo 3 > /proc/sys/vm/drop_caches" for the OS cache
>>
>
> yeah -- good point. aside: does that also drop cache on the drive/raid card?
no -- good point too ! (damn! how SAN users will do...maybe EMC or
other are good enough to provide some control panel for that ? )
and as I read on the link provided by Tomas, it is better to issue a
'sync' before trying to drop cache (I do that sometime, but postgresql
flush its write before shutdown, so I expected the dirty pages in OS
cache not to be relative to postgresql files.)
--
Cédric Villemain 2ndQuadrant
http://2ndQuadrant.fr/ PostgreSQL : Expertise, Formation et Support