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Re: Anything to be gained from a 'Postgres Filesystem'?

From: "Leeuw van der, Tim" <tim(dot)leeuwvander(at)nl(dot)unisys(dot)com>
To: <matt(at)ymogen(dot)net>, <pgsql-performance(at)postgresql(dot)org>
Subject: Re: Anything to be gained from a 'Postgres Filesystem'?
Date: 2004-10-21 08:27:22
Message-ID: BF88DF69D9E2884B9BE5160DB2B97A85010D6EAE@nlshl-exch1.eu.uis.unisys.com (view raw or flat)
Thread:
Lists: pgsql-performance
Hiya,

Looking at that list, I got the feeling that you'd want to push that PG-awareness down into the block-io layer as well, then, so as to be able to optimise for (perhaps) conflicting goals depending on what the app does; for the IO system to be able to read the apps mind it needs to have some knowledge of what the app is / needs / wants and I get the impression that this awareness needs to go deeper than the FS only.

--Tim

(But you might have time to rewrite Linux/BSD as a PG-OS? just kidding!)

-----Original Message-----
From: pgsql-performance-owner(at)postgresql(dot)org [mailto:pgsql-performance-owner(at)postgresql(dot)org]On Behalf Of Matt Clark
Sent: Thursday, October 21, 2004 9:58 AM
To: pgsql-performance(at)postgresql(dot)org
Subject: [PERFORM] Anything to be gained from a 'Postgres Filesystem'?


I suppose I'm just idly wondering really.  Clearly it's against PG
philosophy to build an FS or direct IO management into PG, but now it's so
relatively easy to plug filesystems into the main open-source Oses, It
struck me that there might be some useful changes to, say, XFS or ext3, that
could be made that would help PG out.

I'm thinking along the lines of an FS that's aware of PG's strategies and
requirements and therefore optimised to make those activities as efiicient
as possible - possibly even being aware of PG's disk layout and treating
files differently on that basis.

Not being an FS guru I'm not really clear on whether this would help much
(enough to be worth it anyway) or not - any thoughts?  And if there were
useful gains to be had, would it need a whole new FS or could an existing
one be modified?

So there might be (as I said, I'm not an FS guru...):
* great append performance for the WAL?
* optimised scattered writes for checkpointing?
* Knowledge that FSYNC is being used for preserving ordering a lot of the
time, rather than requiring actual writes to disk (so long as the writes
eventually happen in order...)?


Matt



Matt Clark
Ymogen Ltd
P: 0845 130 4531
W: https://ymogen.net/
M: 0774 870 1584
 


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