Tom Lane a écrit :
> Guillaume Lelarge <guillaume@lelarge.info> writes:
>> Tom Lane a écrit :
>>> What do you have shared_buffers set to? I think you might be getting
>>> fooled by top's treatment of shared memory (ie, it starts to count
>>> shared pages after the process touches them for the first time).
>
>> That's what I thought at first when I saw Marc's email. I tried his
>> example many times, with different values for shared_buffers. RSS column
>> climbs until it reaches more or less the shared_buffers configuration.
>> But, if I launch another psql, this process will have a much lower value
>> on the RSS column. Shouldn't it get the RSS at the same value, even when
>> the process starts ?
>
> No, that's exactly the point. Linux top includes in a process's
> reported size its actual private space, plus however many pages of
> shared memory that process has physically accessed so far. So any PG
> backend that's doing a material amount of table access is going to show
> an RSS that starts low and creeps up to roughly the size of your shared
> memory block, quite independently of what its actual private space usage
> is. It's just a matter of how many buffers it has had occasion to use.
>
> This is all pretty OS-dependent. Some systems don't count shared memory
> at all (HPUX seems not to), and some other ones report a separate total
> for shared memory so that you can mentally subtract it.
>
Forgot to thank you for the answer... Thanks :)
--
Guillaume.
http://www.postgresqlfr.org
http://dalibo.com