From: | Cédric Villemain <cedric(dot)villemain(at)dalibo(dot)com> |
---|---|
To: | Josh Berkus <josh(at)agliodbs(dot)com> |
Cc: | pgsql-hackers(at)postgresql(dot)org, jd(at)commandprompt(dot)com, Robert Haas <robertmhaas(at)gmail(dot)com>, Greg Stark <gsstark(at)mit(dot)edu>, marcin mank <marcin(dot)mank(at)gmail(dot)com> |
Subject: | Re: per table random-page-cost? |
Date: | 2009-10-26 17:19:44 |
Message-ID: | 200910261819.45107.cedric.villemain@dalibo.com |
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Lists: | pgsql-hackers |
Le samedi 24 octobre 2009 01:04:19, Josh Berkus a écrit :
> Cedric,
>
> > ase is a table containing 29 GB of bytea in a database of 52 GB. Every
> > row on the 29GB table is grab only few times. And it will just renew OS
> > cache memory every time (the server have only 8GB of ram).
> > So when I remove this table (not the index) from the OS cache memory, I
> > keep more interesting blocks in the OS cache memory.
>
> effective_cache_size doesn't control what gets cached, it just tells the
> planner about it.
>
> Now, if we had an OS which could be convinced to handle caching
> differently for different physical devices, then I could see wanting
> this setting to be per-tablespace. For example, it would make a lot of
> sense not to FS-cache any data which is on a ramdisk or superfast SSD
> array. The same with archive data which you expected to be slow and
> infrequently accessed on a NAS device. If your OS can do that, while
> caching data from other sources, then it would make sense.
>
> However, I don't know any current OS which allows for this. Does anyone
> else?
Isn't it what "fadvise -dontneed" let you do ?
Josh, I talk about effective_cache_size per tablespace *exactly* for the
reason you explain.
--
Cédric Villemain
Administrateur de Base de Données
Cel: +33 (0)6 74 15 56 53
http://dalibo.com - http://dalibo.org
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