Re: [GENERAL] PITR - base backup question

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.