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Re: WAL files during a backup

From: <steve(at)outtalimits(dot)com(dot)au>
To: windsurferdrew-pg(at)yahoo(dot)com
Cc: pgsql-admin(at)postgresql(dot)org
Subject: Re: WAL files during a backup
Date: 2008-08-28 23:10:44
Message-ID: f3dcb7182f2491f79cfdd560cd3f713c@127.0.0.1 (view raw or flat)
Thread:
Lists: pgsql-admin
Hey Drew,

Correct. This will all depend on what sort of backup system you are after.

If you want to recover up to its existing state, you will need a script
that will nab the current log, located in the x_log dir, and backup this up
every x minutes. Along with this you will be backing up your WAL's. You can
add the current X log to the WAL and recover your DB to its existing state.


On Thu, 28 Aug 2008 05:24:56 -0700 (PDT), windsurferdrew-pg(at)yahoo(dot)com
wrote:
> Thanks Steve.
> 
> If I understand your comment regarding the 16MB limit, it means I should
> not worry about the WAL file not being copied to the archive directory.
> 
> 
> I hope this also means a subsequent attempt to restore the db will
> successfully work since the WAL file is still in the pg_xlog directory.
> 
> Drew
>  
> 
> ----- Original Message ----
> From: "steve(at)outtalimits(dot)com(dot)au" <steve(at)outtalimits(dot)com(dot)au>
> To: windsurferdrew-pg(at)yahoo(dot)com
> Cc: pgsql-admin(at)postgresql(dot)org
> Sent: Wednesday, August 27, 2008 5:31:30 PM
> Subject: Re: [ADMIN] WAL files during a backup
> 
> This WAL wont get copied to the archive directory until it reaches 16MB
> worth of transactional data. I will actually be testing today for work,
if
> I can grab the latest xlog and this can be used in the restore aswell as
> archived WAL's
> 
> I will let you know the results, unless some1 else already knows.?
> 
> On Wed, 27 Aug 2008 13:49:13 -0700 (PDT), windsurferdrew-pg(at)yahoo(dot)com
> wrote:
>> Steve, thanks for your response and your question.
>> 
>> Ok, here is some clarification on the WAL file name used in the example
>> below.
>> 
>> The WAL file name I used in the example is actually
>> 000000010000000000000088, and the backup file name is
>> 000000010000000000000088.0089ED8C.backup.
>> 
>> The WAL file 000000010000000000000088 exists in the data/pg_xlog
> directory
>> after the backup run is completed. The problem for me is that it wasn't
>> copied to the archive directory.
>> 
>> 
>> Since this is a test machine and not much db activity occurring on this
>> server, there have been 6 additional WAL files added to the pg_xlog
>> directory in the last 6 hours since the last backup was performed.
>> 
>> Drew
>> 
>> 
>> ----- Original Message ----
>> From: "steve(at)outtalimits(dot)com(dot)au" <steve(at)outtalimits(dot)com(dot)au>
>> To: windsurferdrew-pg(at)yahoo(dot)com
>> Cc: pgsql-admin(at)postgresql(dot)org
>> Sent: Wednesday, August 27, 2008 4:36:24 PM
>> Subject: Re: [ADMIN] WAL files during a backup
>> 
>> 00000001000000000000223387  would usually be the next WAL to be written.
>> How often are you WALs written out?
>> 
>> On Wed, 27 Aug 2008 07:07:17 -0700 (PDT), windsurferdrew-pg(at)yahoo(dot)com
>> wrote:
>>> I have a question regarding the WAL files that are moved during a
> backup
>> to
>>> the "archive directory".
>>> 
>>> I have setup the postgresql.conf file to have the following archive
>>> command:
>>> 
>>> archive_command = 'cp -i %p /var/lib/pgsql/backups/%f </dev/null'
>>> 
>>> Environment: 
>>> PG Version 8.1.4
>>> OS: Linux 2.6.18-8.el5
>>> 
>>> After I have run the pg_hotbackup script, the backups directory
> contains
>>> only 2 files:
>>> 1. The gzipped tar file pg_hotbackup_<timestamp>.tar.gz, and
>>> 2. a WAL file ".backup" file, (for example
>>> 00000001000000000000223387.0089ED8C.backup)
>>> 
>>> The actual WAL file did not get copied to the backups directory. From
>> the
>>> example above, I would have expected at least 1  WAL file named
>>> 00000001000000000000223387 to be in the backups directory.
>>> 
>>> My questions are:
>>> 1. Is this normal behavior? (perhaps no activity in the DB to cause a
>> WAL
>>> file write during the backup?)
>>> 2. If I try to restore the DB without this WAL file, will the restore
>>> fail?
>>> 
>>> Thanks in advance
>>> 
>>> Drew 
>>> 
>>> 
>>>
> 
> 
>

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