Re: [GENERAL] PITR - base backup question - Mailing list pgsql-admin

I have what I have sometimes called a 'tepid spare' backup.  Once a week I copy the physical files over to another system (actually to two of them) and every few hours I make sure the archived WAL log files are in sync (using rsync.)

Anyway, here's the cookbook guide I wrote for updating one of the backup servers, which I have used several times, so I don't have to rediscover the steps each time.  I think it has sufficient detail that someone other than me could follow them.  Obviously it would have to be changed to apply to your file organization scheme.

Enjoy!
--
Mike Nolan


How to restore the PostgreSQL low level backup tar files and WAL files
to do a point-in-time recovery (PITR) files on a backup server.

This note will explain how to perform a point-in-time recovery of the
PostgreSQL database using the low-level backup files and the archived
WAL (write-ahead log) files.  (These steps should work on either server, with any differences in actual file locations dealt with using symbolic links.)

The low level backup files and WAL log files should already be present
on the backup servers.  The low level tar files files are copied when they
are created (usually early on a Tuesday morning each week) and the WAL log
files are rsync'ed to both servers every few hours so that both backup
servers should have files enabling them to be restored to a state that is
no more than a few hours out of sync with the live database server.  (In
the future, we hope to keep one of the backup servers in full real-time
synchronization with the live server, using a different technique.)

The steps given below will generally take 3-5 hours to run, depending
on how many archived log files need to be processed when the PostgreSQL
server is restarted.

These instructions assume some familiarity with Unix/Linux system
administration tools, including the vi editor, and with database
administration procedures, though not necessarily detailed knowledge
of PostgreSQL.

For more details, see chapter 23 of the PostgreSQL documentation,
especially section 23.3.  The documentation for version 8.2 is at
http://www.postgresql.org/docs/8.2/static/backup.html


1.  su to root on the backup server that the restore will be performed on

2.  su to postgres (su - postgres)

3.  Shut down the Postgresql server running on the backup server, if any
         pg_ctl stop
    (Use 'ps ax' to make sure the server is stopped.)


4.  cd to /disk1/postgres/data and copy two files to /tmp

     cd /disk1/postgres/data
     cp pg_hba.conf /tmp
     cp recovery.done /tmp

5.  Delete the entire contents of the /disk1/postgres/data directory tree.
    MAKE ABSOLUTELY SURE YOU ARE IN THE /disk1/postgres/data directory!

     cd /disk1/postgres/data
     pwd
     rm -rf *

6.  Restore the tar file for the low-level backup from the live server

    tar xvf /usr/local/pgsql/tardir/pg_part1.tar

    (This restore may take 2-3 hours)

7.  Remove the PostgreSQL log file and the WAL files that were restored
    from the tar archive
  
    rm log.out
    cd pg_xlog
    rm 00*

    (do not remove the archive_status subdirectory)

8.  Copy the pg_hba.conf file back from the /tmp directory

    cd /disk1/postgres/data
    cp /tmp/pg_hba.conf .

    (This is necessary to keep this database server configured for restricted
    access.  If more expansive access is needed the restored pg_hba.conf
    file may be more appropriate.)

9. Copy the recovery configuration file from the /tmp directory (changing
    the file name)

   cp /tmp/recovery.done recovery.conf

   (This file may be edited to do a point-in-time recovery other than
   to the end of the PITR log files, see the PostgreSQL documentation for
   details.) 

10. Delete the entire contents of the /disk2/postgres/data directory tree.
    MAKE ABSOLUTELY SURE YOU ARE IN THE /disk2/postgres/data directory!

     cd /disk2/postgres/data
     pwd
     rm -rf *

11. Restore the 2nd tar archive

    tar xvf /usr/local/pgsql/tardir/pg_part2.tar

    (This restore may take around a half hour)

12. Go to the directory where the WAL files have been archived on
    the server and remove all files older than the file matching the
    last .backup file.  The fastest way to do this is as follows:

    cd /usr/local/pgsql/archivedir
    ls -1 > files

    This will produce a file listing all files in the archivedir directory.
   
    Now edit that file (using vi) to take out all lines after the
    latest 'backup' file (including the file just ahead of that backup
    file, since it is actually the first file that needs to be processed.
    (Note:  These ones after the latest backup file are the files we're
    NOT going to delete, so we don't want those file names in this text file.)

    For example, the directory list may look like this:

       00000001000000960000000A
       00000001000000960000000B
       00000001000000960000000C
       00000001000000960000000C.004027C0.backup
       00000001000000960000000D

    There will generally be several files with the name ending in 'backup',
    find the most recent one (ie, the last one in the file.)

    In this case, the fie with the name ending in '000C' needs to be
    restored, along with all subsequent files, so in this case we would
    delete all lines from the one ending in '000C' to the end of the edit
    buffer, then edit the lines to change the lines into 'rm' commands,
    ie, something like this:

       rm 00000001000000960000000A
       rm 00000001000000960000000B


    Save the edited file, then execute it

       sh -x files

13. You are now ready to restart PostgreSQL and have it process all the
    archived log files:

    pg_ctl -l /usr/local/pgsql/data/log.out start

14. While the WAL files are being processed, a 'ps -ax' display will
    have lines in it that look something like this:

       28039 pts/0    S      0:00 /disk1/postgres/pgsql/bin/postgres
       28040 ?        Ds     0:00 postgres: startup process

    You can also look at the /usr/local/pgsql/data/log.out file to see
    which WAL file it is currently processing:

    tail /usr/local/pgsql/data/log.out

    Once all the WAL files have been processed (which could take an
    hour or longer, depending on how many WAL files need to be processed,
    'ps -ax' will look more like this:

       28039 pts/0    S      0:00 /disk1/postgres/pgsql/bin/postgres
       28310 ?        Ss     0:00 postgres: writer process
       28311 ?        Ss     0:00 postgres: archiver process
       28312 ?        Ss     0:00 postgres: stats collector process
 
    Once this happens, the backup database server is ready for use. 
    However, it will only be as current as the most recent WAL file that
    was processed, and in order to bring it to a more current state all of
    the steps given above have to be performed again.