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Re: Raw devices vs. Filesystems

Remarkable, perhaps, to you. Not in the Informix world. But irrelevant to postgres, no ?

-----Original Message-----
From: Chris Browne [mailto:cbbrowne@acm.org]
Sent: Tuesday, April 06, 2004 1:57 PM
To: pgsql-admin@postgresql.org
Subject: Re: [ADMIN] Raw devices vs. Filesystems


gsw@globexplorer.com ("Gregory S. Williamson") writes:
> No point to beating a dead horse (other than the sheer joy of the
> thing) since postgres does not have raw device support, but ...  raw
> devices, at least on solaris, are about 10 times as fast as cooked
> file systems for Informix. This might still be a gain for postgres'
> performance, but the portability issues remain.

That claim seems really rather remarkable.

It implies an entirely stunning degree of inefficiency in the
implementation of filesystems on Solaris.

The amount of indirection involved in walking through i-nodes and such
is something I would expect to introduce some percentage of
performance loss, but for it to introduce overhead of over 900%
presumably implies that Sun (and/or Veritas) got something really
horribly wrong.
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gsw (2)
4/6/2004 9:23:42 PM
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Note that the innefficiency could well lie with Informix's file system 
interfacing as easily as it could lie with the operating system.  Do they 
charge extra for being able to access raw devices or somehow make more 
money by supporting them?  If so, there could be a clear business case for 
lots of uwaits() in the code path that handles file systems.

I'm just saying it's a possibility.

On Tue, 6 Apr 2004, Gregory S. Williamson wrote:

> Remarkable, perhaps, to you. Not in the Informix world. But irrelevant to postgres, no ?
> 
> -----Original Message-----
> From: Chris Browne [mailto:cbbrowne@acm.org]
> Sent: Tuesday, April 06, 2004 1:57 PM
> To: pgsql-admin@postgresql.org
> Subject: Re: [ADMIN] Raw devices vs. Filesystems
> 
> 
> gsw@globexplorer.com ("Gregory S. Williamson") writes:
> > No point to beating a dead horse (other than the sheer joy of the
> > thing) since postgres does not have raw device support, but ...  raw
> > devices, at least on solaris, are about 10 times as fast as cooked
> > file systems for Informix. This might still be a gain for postgres'
> > performance, but the portability issues remain.
> 
> That claim seems really rather remarkable.
> 
> It implies an entirely stunning degree of inefficiency in the
> implementation of filesystems on Solaris.
> 
> The amount of indirection involved in walking through i-nodes and such
> is something I would expect to introduce some percentage of
> performance loss, but for it to introduce overhead of over 900%
> presumably implies that Sun (and/or Veritas) got something really
> horribly wrong.
> 


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0
scott
4/6/2004 10:46:31 PM
 > gsw@globexplorer.com ("Gregory S. Williamson") writes:
 >>No point to beating a dead horse (other than the sheer joy of the
 >>thing) since postgres does not have raw device support, but ...  raw
 >>devices, at least on solaris, are about 10 times as fast as cooked
 >>file systems for Informix. This might still be a gain for postgres'
 >>performance, but the portability issues remain.

 > From: Chris Browne [mailto:cbbrowne@acm.org]
 > That claim seems really rather remarkable.
 > It implies an entirely stunning degree of inefficiency in the
 > implementation of filesystems on Solaris.
 > The amount of indirection involved in walking through i-nodes and such
 > is something I would expect to introduce some percentage of
 > performance loss, but for it to introduce overhead of over 900%
 > presumably implies that Sun (and/or Veritas) got something really
 > horribly wrong.

Gregory S. Williamson wrote:
> Remarkable, perhaps, to you. Not in the Informix world. But
 > irrelevant to postgres, no ?

I too am a little surprised by those numbers, but I think the potential 
for a performance gain of that order is relevant.

As I once heard someone remark: "When show up at a pool hall talking 
those kind of odds, well, people start making phone calls."

- Marsh


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marsh
4/7/2004 2:56:38 AM
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