Re: [PERFORM] ext3 journalling type

2004-11-08 Thread Bruce Momjian
Dawid Kuroczko wrote:
 The ext3fs allows to selet type of journalling to be used with
 filesystem.  Journalling pretty much mirrors the work of WAL
 logging by PostgreSQL...  I wonder which type of journalling
 is best for PgSQL in terms of performance.
 Choices include:
   journal
  All data is committed into the  journal  prior  to  being
  written into the main file system.
   ordered
  This  is  the  default mode.  All data is forced directly
  out to the main file system prior to its  metadata  being
  committed to the journal.
   writeback
  Data ordering is not preserved - data may be written into
  the main file system after its metadata has been  commit-
  ted  to the journal.  This is rumoured to be the highest-
  throughput option.  It guarantees  internal  file  system
  integrity,  however  it  can  allow old data to appear in
  files after a crash and journal recovery.
 
 Am I right to assume that writeback is both fastest and at the same
 time as safe to use as ordered?  Maybe any of you did some benchmarks?

Yes.  I have seen benchmarks that say writeback is fastest but I don't
have any numbers handy.

-- 
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Re: [PERFORM] ext3 journalling type

2004-11-08 Thread Matt Clark
 Am I right to assume that writeback is both fastest and at 
 the same time as safe to use as ordered?  Maybe any of you 
 did some benchmarks?

It should be fastest because it is the least overhead, and safe because
postgres does it's own write-order guaranteeing through fsync().  You should
also mount the FS with the 'noatime' option.

But  For some workloads, there are tests showing that 'data=journal' can
be the fastest!  This is because although the data is written twice (once to
the journal, and then to its real location on disk) in this mode data is
written _sequentially_ to the journal, and later written out to its
destination, which may be at a quieter time.

There's a discussion (based around 7.2) here:
http://www.kerneltraffic.org/kernel-traffic/kt20020401_160.txt

M


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Re: [PERFORM] ext3 journalling type

2004-11-08 Thread Mark Wong
I have some data here, no detailed analyses though:

http://www.osdl.org/projects/dbt2dev/results/fs/

Mark

On Mon, Nov 08, 2004 at 01:26:09PM +0100, Dawid Kuroczko wrote:
 The ext3fs allows to selet type of journalling to be used with
 filesystem.  Journalling pretty much mirrors the work of WAL
 logging by PostgreSQL...  I wonder which type of journalling
 is best for PgSQL in terms of performance.
 Choices include:
   journal
  All data is committed into the  journal  prior  to  being
  written into the main file system.
   ordered
  This  is  the  default mode.  All data is forced directly
  out to the main file system prior to its  metadata  being
  committed to the journal.
   writeback
  Data ordering is not preserved - data may be written into
  the main file system after its metadata has been  commit-
  ted  to the journal.  This is rumoured to be the highest-
  throughput option.  It guarantees  internal  file  system
  integrity,  however  it  can  allow old data to appear in
  files after a crash and journal recovery.
 
 Am I right to assume that writeback is both fastest and at the same
 time as safe to use as ordered?  Maybe any of you did some benchmarks?
 
 Regards,
  Dawid
 


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Re: [PERFORM] ext3 journalling type

2004-11-08 Thread Josh Berkus
Matt,

 It should be fastest because it is the least overhead, and safe because
 postgres does it's own write-order guaranteeing through fsync().  You
 should also mount the FS with the 'noatime' option.

This, of course, assumes that PostgreSQL is the only thing on the partition.  
Which is a good idea in general, but not to be taken for granted ...

-- 
Josh Berkus
Aglio Database Solutions
San Francisco

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