Thread: WAL FILES
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. Regards, -- 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)
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, Pennsylvania19026
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, Pennsylvania19026