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

On 04/22/2014 08:40 AM, Wang, Mary Y 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 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