WAL FILES

Olivier PRENANT wrote:

Hi every one.

I just moved (at last!) to 7.2.1. Works like a charm...
I'm suprised though by the number of WAL files.

I have 8 files where postgresql.conf says WAL_FILES=4.

What did I miss ? (I have no outstanding transaction)

FWIW, t's on UW711.

No, you are fine. The current GUC params are confusing. I did update
the documentation for 7.3, but I plan to reorganize those params to be
more meaningful.

Actually, I have in TODO:

Remove wal_files postgresql.conf option because WAL files are now
recycled

because the param no longer controls what you think it controls. In 7.1
WAL files where not recycled, so WAL_FILES was used to pre-allocate
files so there wasn't as much happening during checkpoint. Now, with
recycling, there is no need.

-- 
  Bruce Momjian                        |  http://candle.pha.pa.us
  pgman@candle.pha.pa.us               |  (610) 853-3000
  +  If your life is a hard drive,     |  830 Blythe Avenue
  +  Christ can be your backup.        |  Drexel Hill, Pennsylvania 19026

Hi Bruce,

Thank you for your reply. It makes a lot of sense!
However I don't really understand why we can't control the NUMBER of
files.
Are the 8 files I see a maximum usage when I reloaded the databases on the
ne system or is it some sort of "plugged in value"?

Thank you for your explanation.
On Mon, 27 May 2002, Bruce Momjian wrote:

Date: Mon, 27 May 2002 17:17:58 -0400 (EDT)
From: Bruce Momjian <pgman@candle.pha.pa.us>
To: ohp@pyrenet.fr
Cc: pgsql-hackers list <pgsql-hackers@postgresql.org>
Subject: Re: [HACKERS] WAL FILES

Olivier PRENANT wrote:

Hi every one.

I just moved (at last!) to 7.2.1. Works like a charm...
I'm suprised though by the number of WAL files.

I have 8 files where postgresql.conf says WAL_FILES=4.

What did I miss ? (I have no outstanding transaction)

FWIW, t's on UW711.

No, you are fine. The current GUC params are confusing. I did update
the documentation for 7.3, but I plan to reorganize those params to be
more meaningful.

Actually, I have in TODO:

Remove wal_files postgresql.conf option because WAL files are now
recycled

because the param no longer controls what you think it controls. In 7.1
WAL files where not recycled, so WAL_FILES was used to pre-allocate
files so there wasn't as much happening during checkpoint. Now, with
recycling, there is no need.

--
Olivier PRENANT Tel: +33-5-61-50-97-00 (Work)
Quartier d'Harraud Turrou +33-5-61-50-97-01 (Fax)
31190 AUTERIVE +33-6-07-63-80-64 (GSM)
FRANCE Email: ohp@pyrenet.fr
------------------------------------------------------------------------------
Make your life a dream, make your dream a reality. (St Exupery)

8 is the maximum unless WAL files have to be created _while_ the
checkpoint is taking place.

Current CVS SGML has:

The number of 16MB segment files will always be at least
<varname>WAL_FILES</varname> + 1, and will normally not exceed
<varname>WAL_FILES</varname> + MAX(<varname>WAL_FILES</varname>,
<varname>CHECKPOINT_SEGMENTS</varname>) + 1.

The real driver here is CHECKPOINT_SEGMENTS because WAL_FILES is going
away in 7.3 and will just be dynamically used. The typical setup is
checkpoint_segments files. I will also add better reporting so you can
know if your checkpoint_segments is too small, causing checkpoints too
frequently.

---------------------------------------------------------------------------

Olivier PRENANT wrote:

Hi Bruce,

Thank you for your reply. It makes a lot of sense!
However I don't really understand why we can't control the NUMBER of
files.
Are the 8 files I see a maximum usage when I reloaded the databases on the
ne system or is it some sort of "plugged in value"?

Thank you for your explanation.
On Mon, 27 May 2002, Bruce Momjian wrote:

Date: Mon, 27 May 2002 17:17:58 -0400 (EDT)
From: Bruce Momjian <pgman@candle.pha.pa.us>
To: ohp@pyrenet.fr
Cc: pgsql-hackers list <pgsql-hackers@postgresql.org>
Subject: Re: [HACKERS] WAL FILES

Olivier PRENANT wrote:

Hi every one.

I just moved (at last!) to 7.2.1. Works like a charm...
I'm suprised though by the number of WAL files.

I have 8 files where postgresql.conf says WAL_FILES=4.

What did I miss ? (I have no outstanding transaction)

FWIW, t's on UW711.

No, you are fine. The current GUC params are confusing. I did update
the documentation for 7.3, but I plan to reorganize those params to be
more meaningful.

Actually, I have in TODO:

Remove wal_files postgresql.conf option because WAL files are now
recycled

because the param no longer controls what you think it controls. In 7.1
WAL files where not recycled, so WAL_FILES was used to pre-allocate
files so there wasn't as much happening during checkpoint. Now, with
recycling, there is no need.

--
Olivier PRENANT Tel: +33-5-61-50-97-00 (Work)
Quartier d'Harraud Turrou +33-5-61-50-97-01 (Fax)
31190 AUTERIVE +33-6-07-63-80-64 (GSM)
FRANCE Email: ohp@pyrenet.fr
------------------------------------------------------------------------------
Make your life a dream, make your dream a reality. (St Exupery)

-- 
  Bruce Momjian                        |  http://candle.pha.pa.us
  pgman@candle.pha.pa.us               |  (610) 853-3000
  +  If your life is a hard drive,     |  830 Blythe Avenue
  +  Christ can be your backup.        |  Drexel Hill, Pennsylvania 19026