Обсуждение: WAL Queries

I installed PGSQL on Windows XP. I ran:

Select pg_start_backup('label');

It responded: "Archive disabled"

Is WAL archiving disabled by default?
Can this feature be enabled while installing PGSQL?
Can I change the path of the logs to another partition on my hard disk?
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RPK wrote:
> I installed PGSQL on Windows XP. I ran:
>
> Select pg_start_backup('label');
>
> It responded: "Archive disabled"
>
> Is WAL archiving disabled by default?
> Can this feature be enabled while installing PGSQL?
> Can I change the path of the logs to another partition on my hard disk?

Enable it in the "Write Ahead Log" section of postgresql.conf file in
the PGDATA directory.

--
Paul Lambert
Database Administrator
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Before modifying postgresql.conf, do I need to stop PGSQL service?


>Enable it in the "Write Ahead Log" section of postgresql.conf file in
>the PGDATA directory.

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RPK wrote:
> Before modifying postgresql.conf, do I need to stop PGSQL service?
>
>
>> Enable it in the "Write Ahead Log" section of postgresql.conf file in
>> the PGDATA directory.
>

You need to restart PostgreSQL after the file has been modified - it
does not need to be shut down whilst the modification is being
undertaken, just a quick restart once you have saved the file.

--
Paul Lambert
Database Administrator
AutoLedgers

How to change the path of WAL? How much free space to leave on hard disk for
effective performance? Since it is disabled by default, is it insignificant
to ENABLE it?


>You need to restart PostgreSQL after the file has been modified - it
>does not need to be shut down whilst the modification is being
>undertaken, just a quick restart once you have saved the file.

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RPK wrote:
> How to change the path of WAL? How much free space to leave on hard disk for
> effective performance? Since it is disabled by default, is it insignificant
> to ENABLE it?
>

Just change the settings under the WAL section of the config file. The
WAL files themselves will end up in the pg_xlog directory in pgdata, but
you can define the archive_command setting to archive the files off to
another directory.

Refer to the WAL section of the manual for details on what to set the
settings to.
http://www.postgresql.org/docs/8.2/interactive/wal-configuration.html

How much hard-disk space you need is largely dependant on the size of
your database and the size and frequency of updates coming through.

--
Paul Lambert
Database Administrator
AutoLedgers

On 8/5/07, Paul Lambert <paul.lambert@autoledgers.com.au> wrote:
> RPK wrote:
> > Before modifying postgresql.conf, do I need to stop PGSQL service?
> >
> >
> >> Enable it in the "Write Ahead Log" section of postgresql.conf file in
> >> the PGDATA directory.
> >
>
> You need to restart PostgreSQL after the file has been modified - it
> does not need to be shut down whilst the modification is being
> undertaken, just a quick restart once you have saved the file.

This is not quite correct: you may change archive_command in
postgresql.conf and do a pg_ctl reload to bring in the setting without
a full restart of the server.

Also, I wold like to make a small clarification: In PostgreSQL, WAL is
always on and there is no way to turn it off....the archive_command
allows you to intercept the WAL files as they are written to disk and
do additional things with them.  Normally this would involve directing
them to storage or a standby server.  Saving off WAL files is only
useful if you take a filesystem snapshot of the database first...the
pg_start_backup facilitates this.

merlin