Обсуждение: How does the WAL work? Need to recovery the database to a specific point of time

Hi All,

 

I’d like to recovery the database to a specific point of time. I see some WAL files in the pg_xlog directories.

I read some blogs, and some have indicated that a recovery.conf needs to be updated.  I do not see a recovery.conf file in the $PG_DATA directory ( I see pg_hba.conf and postgresql.conf). 

 

1.       Do I need to create a recovery.conf file? 

2.       What specific settings should I set? 

3.       How do I ensure that postgres will read the recovery.conf file? 

4.       What is the start/stop postgres command to use when working with a recovery.conf file?

 

I am running on Postgres 8.4.11 and RHEL 6.4.

 

Point-in-time recovery is not something that can typically be performed arbitrarily "after the fact" - you need to have established the necessary backup and archiving in advance.

This capability is essentially a useful side-effect of the process through which PostgreSQL recovers from an inconsistent state following a power-failure or other disruptive event by replaying the appropriate WAL files.

Point-in-time recovery assumes you have both a *file-system* backup (not a pg_dump) of the PostgreSQL data files that was completed prior to the point in time to which you wish to recover *and* all the write-ahead log (WAL) files created from when the file-system was backed-up and the point to which you wish to recover. This is typically set up through a combination of scheduled file-system backups and archiving of WAL files.

WAL files are not stored indefinitely but rather are rotated and optionally archived based on your configuration settings.

If you have the base file-system backup and all the required WAL files, have a look at http://www.postgresql.org/docs/8.4/static/continuous-archiving.html

Cheers,
Steve

On 22 April 2014 16:40, Wang, Mary Y <mary.y.wang@boeing.com> wrote:
> Hi All,
>
>
>
> I’d like to recovery the database to a specific point of time. I see some
> WAL files in the pg_xlog directories.
>
> I read some blogs, and some have indicated that a recovery.conf needs to be
> updated.  I do not see a recovery.conf file in the $PG_DATA directory ( I
> see pg_hba.conf and postgresql.conf).
>
>
>
> 1.       Do I need to create a recovery.conf file?
>
> 2.       What specific settings should I set?
>
> 3.       How do I ensure that postgres will read the recovery.conf file?
>
> 4.       What is the start/stop postgres command to use when working with a
> recovery.conf file?
>
>
>
> I am running on Postgres 8.4.11 and RHEL 6.4.

Point in Time Recovery is supported, though you have to have done some
planning beforehand. The settings and commands you'll use depend upon
the exact nature of your problem and the backups and other file copies
you possess.

http://www.postgresql.org/docs/devel/static/continuous-archiving.html
etc

--
 Simon Riggs                   http://www.2ndQuadrant.com/
 PostgreSQL Development, 24x7 Support, Training & Services