Re: how to recover database back from /data folder - Mailing list pgsql-admin

On 12/10/06, yogesh@banasdairy.coop <yogesh@banasdairy.coop> wrote:
> hi to all
> last time
> my redhat 9 is corrupt so at that time itake backup of my postgresql database
> /data folder

Yogesh,

Backup of postgresql is done by a specific process.
Simply copying /data ( PGDATA)  is not the way (generally)
have you been doing pg_dump or pg_dumpall for your database
regularly ?

http://www.postgresql.org/docs/8.0/static/backup-file.html

22.2. File system level backup

 An alternative backup strategy is to directly copy the files that
PostgreSQL uses to store the data in the database. In Section 16.2 it
is explained where these files are located, but you have probably
found them already if you are interested in this method. You can use
whatever method you prefer for doing usual file system backups, for
example

tar -cf backup.tar /usr/local/pgsql/data

There are two restrictions, however, which make this method
impractical, or at least inferior to the pg_dump method:

   1.

      The database server must be shut down in order to get a usable
backup. Half-way measures such as disallowing all connections will not
work (mainly because tar and similar tools do not take an atomic
snapshot of the state of the file system at a point in time).
Information about stopping the server can be found in Section 16.6.
Needless to say that you also need to shut down the server before
restoring the data.
   2.

      If you have dug into the details of the file system layout of
the database, you may be tempted to try to back up or restore only
certain individual tables or databases from their respective files or
directories. This will not work because the information contained in
these files contains only half the truth. The other half is in the
commit log files pg_clog/*, which contain the commit status of all
transactions. A table file is only usable with this information. Of
course it is also impossible to restore only a table and the
associated pg_clog data because that would render all other tables in
the database cluster useless. So file system backups only work for
complete restoration of an entire database cluster.



>
> so after two days i restall the redhat 9
> than i try to copy old /data folder over newly /data folder
>
> but it does not start postgresql service
> so please any one give me solution
>
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