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Re: WAL archiving

From: "Praveen Kumar \(TUV\)" <praveen(dot)k(at)renaissance-it(dot)com>
To: "Vishal Arora" <aroravishal22(at)hotmail(dot)com>,"Shilpa Sudhakar" <ssudhakar(at)internode(dot)com(dot)au>
Cc: <pgsql-admin(at)postgresql(dot)org>
Subject: Re: WAL archiving
Date: 2008-02-25 06:38:03
Message-ID: 84D57263D486374587DA0820E60A2CC601B08C2A@srit_mail.renaissance-it.com (view raw or flat)
Thread:
Lists: pgsql-admin
Hello,

If the machine where we have make  setup for warm standby database goes
down and we restart this machine again ,then what will  be happen for 

Our warm standby database ,will it again start applying archive log from
starting point ( archive log generated after taking online backup) or
from that point where

It has leaved before machine was go down ?

 

 

  _____  

From: pgsql-admin-owner(at)postgresql(dot)org
[mailto:pgsql-admin-owner(at)postgresql(dot)org] On Behalf Of Vishal Arora
Sent: Monday, February 25, 2008 11:30 AM
To: Shilpa Sudhakar
Cc: pgsql-admin(at)postgresql(dot)org
Subject: Re: [ADMIN] WAL archiving

 







  _____  


> Date: Mon, 25 Feb 2008 15:30:46 +1030
> From: ssudhakar(at)internode(dot)com(dot)au
> To: aroravishal22(at)hotmail(dot)com
> CC: pgsql-admin(at)postgresql(dot)org
> Subject: Re: [ADMIN] WAL archiving
> 
> Thanks a lot Vishal for the info.
> 
> I have one more query postgres automatically cleans the WAL files 
> present in the pg_xlog directory....right?

YES! it actually recycles the files which are of no further intrest.
 
So instead of me creating a separate folder as i've done in my current 
> settings (wal_log), should i need to change the archive_command to
point 
> to pg_xlog directly.

NO! In this case it would try to overwrite the existing WAL files.
pg_xlog already contains the WAL files .. whats the point archiving the
files at the same place. 
 
Refer to Chapter 23.3.1 (8.2) of the Manual - 

"The archive command should generally be designed to refuse to overwrite
any pre-existing archive file. This is an important safety feature to
preserve the integrity of your archive in case of administrator error
(such as sending the output of two different servers to the same archive
directory). It is advisable to test your proposed archive command to
ensure that it indeed does not overwrite an existing file, and that it
returns nonzero status in this case. "


> In this way i can avoid a separate process of deleting old files.
> 
> Please let me know if my understanding is right.
> 
> Thanks and Regards,
> Shilpa
> 
> 
> 
> Vishal Arora wrote:
> >
> >
> >
> >
> >
> >
------------------------------------------------------------------------
> >
> > > Date: Mon, 25 Feb 2008 09:53:35 +1030
> > > From: ssudhakar(at)internode(dot)com(dot)au
> > > To: aroravishal22(at)hotmail(dot)com
> > > Subject: Re: [ADMIN] WAL archiving
> > >
> > > Hi Vishal,
> > >
> > > Below is the setup in the postgresql.conf file
> > >
> > > fsync = true # turns forced synchronization on or off
> > > wal_sync_method = fsync # the default varies across platforms:
> > > #wal_buffers = 8 # min 4, 8KB each
> > > #commit_delay = 0 # range 0-100000, in microseconds
> > > #commit_siblings = 5 # range 1-1000
> > >
> > > # - Checkpoints -
> > >
> > > checkpoint_segments = 3 # in logfile segments, min 1, 16MB each
> > > checkpoint_timeout = 300 # range 30-3600, in seconds
> > > checkpoint_warning = 30 # 0 is off, in seconds
> > >
> > > # - Archiving -
> > >
> > > archive_command = 'cp -i %p /usr/local/var/pgsql/data/wal_log/%f'
> > > # command to use to archive a logfile segment
> > >
> > > Since this is the test system i've put the wal_log folder in the
data
> > > folder itself. But, later on i'll be moving this to a different
disk.
> > >
> > > We have thousands and thousands of records that get inserted and 
> > updated
> > > so the wal logs would be increasing in a large rate. I was
thinking 
> > if i
> > > want to delete the wal logs after a period of time, do i take a
base
> > > backup again and then delete those old files?
> >
> > Not required actually. Once you have base backup and Archived WAL in

> > place, you need not take a base backup again. In case of a crash you

> > just have to restore from the base backup and the server would start

> > in restore mode. In restore.conf file you have to specify the 
> > restore_command - which would point towards the archived WAL files. 
> > Yes Once the WAL has been archived you can delete the old WAL files,

> > which is also done by the postgres itself. It replaces the old(not 
> > required) WAL files with the new one.
> >
> > > Thanks and Regards,
> > > Shilpa
> > >
> > >
> > > Vishal Arora wrote:
> > > >
> > > > Hi Shilpa,
> > > >
> > > > You need not take base backup again and again. You have WAL 
> > Archiveing
> > > > in place, that is enough to restore the database. BTW, what
archiving
> > > > command are you using for WAL Archiving in you postgresql.conf.
> > > >
> > > > - Vishal
> > > >
> > > > 
> >
------------------------------------------------------------------------
> > > >
> > > > > Date: Fri, 22 Feb 2008 09:53:25 +1030
> > > > > From: ssudhakar(at)internode(dot)com(dot)au
> > > > > To: pgsql-admin(at)postgresql(dot)org
> > > > > Subject: [ADMIN] WAL archiving
> > > > >
> > > > > Hi All,
> > > > >
> > > > > I am new to postgres and have been slowly learning the
concepts.
> > > > >
> > > > > Regarding WAL archiving, we first take a base backup and then 
> > save all
> > > > > the wal logs for PITR.
> > > > >
> > > > > Both the base backup and wal logs are stored in another disk.
> > > > >
> > > > > Since the wal logs keep increasing, do we take the base backup

> > every
> > > > now
> > > > > and then so that we can delete the old log files?
> > > > > How often do we take a base filesystem backup keeping in mind 
> > that our
> > > > > systems are 24 x 7.
> > > > >
> > > > > Any suggestions are appreciated.
> > > > >
> > > > > Thanks and Regards,
> > > > > Shilpa
> > > > >
> > > > >
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