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PostgreSQL PITR backup restoration » History » Version 47

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Amit Belani, 08/22/2015 12:22 PM


PostgreSQL PITR backup restoration

This article uses the drivestat database cluster hosted on dmsen03 as an example.

Restore base backup

Identify

Identify the most recent base backup for the database cluster.

If the RAID on the host serving the database is available, identify the recent base backups on it.

[enstore@dmsen03 ~]$ enstore config --show drivestat_server PITR_area
/srv3/enstore/pg_pitr
[enstore@dmsen03 ~]$ ls -lh $(enstore config --show drivestat_server PITR_area)/pg_base_backup/drivestat | tail -2
-rw-r--r-- 1 enstore enstore 2.4M Aug 20 04:30 2015-08-20_04-30-02.tar.xz
-rw-r--r-- 1 enstore enstore 2.4M Aug 21 04:30 2015-08-21_04-30-03.tar.xz

As an alternative, if the RAID on the remote backup host is available, identify the recent base backups on it.

[enstore@dmsen03 ~]$ enstore config --show crons backup_dir
/srv3/enstore/backups
[enstore@dmsen03 ~]$ ls -lh $(enstore config --show crons backup_dir)/pg_base_backup/drivestat | tail -2
-rw-r--r-- 1 enstore enstore 2.4M Aug 20 04:30 2015-08-20_04-30-02.tar.xz
-rw-r--r-- 1 enstore enstore 2.4M Aug 21 04:30 2015-08-21_04-30-03.tar.xz

As a final alternative, if base backups are available on tape only, identify and copy the most recent base backup from tape to disk.

[enstore@dmsen03 ~]$ ls -lh /pnfs/eagle/dmsen-backups/$(date +%Y/%m/%d)/*/*pg_base_backup-drivestat*
-rw-r--r-- 1 enstore enstore 2.4M Aug 21 08:02 /pnfs/eagle/dmsen-backups/2015/08/21/07/srv3-enstore-backups-pg_base_backup-drivestat-2015-08-21_04-30-03.tar.xz
[enstore@dmsen03 ~]$ ENSTORE_CONFIG_HOST_REAL=$ENSTORE_CONFIG_HOST
[enstore@dmsen03 ~]$ enstore config --show crons backup2tape_config_host
conf-stken.fnal.gov
[enstore@dmsen03 ~]$ ENSTORE_CONFIG_HOST=$(enstore config --show crons backup2tape_config_host)
[enstore@dmsen03 ~]$ encp /pnfs/eagle/dmsen-backups/2015/08/21/07/srv3-enstore-backups-pg_base_backup-drivestat-2015-08-21_04-30-03.tar.xz /tmp/
[enstore@dmsen03 ~]$ ls -lh /tmp/srv3-enstore-backups-pg_base_backup-drivestat-2015-08-21_04-30-03.tar.xz
-rw-r--r-- 1 enstore enstore 2.4M Aug 22 07:54 /tmp/srv3-enstore-backups-pg_base_backup-drivestat-2015-08-21_04-30-03.tar.xz
[enstore@dmsen03 ~]$ ENSTORE_CONFIG_HOST=$ENSTORE_CONFIG_HOST_REAL

Extract

Extract the identified base backup into an appropriate empty directory on a node where the database is to be hosted.

[enstore@dmsen03 ~]$ mkdir -m 0700 /tmp/pitr_restore_test1

Note that if "-m 0700" is not specified above, there occurs a fatal error upon starting the database cluster, indicating that the data directory has group or world access, and that its permissions should be u=rwx (0700).

[enstore@dmsen03 ~]$ tar -xf /srv3/enstore/pg_pitr/pg_base_backup/drivestat/2015-08-21_04-30-03.tar.xz -C /tmp/pitr_restore_test1/
[enstore@dmsen03 ~]$ ls /tmp/pitr_restore_test1/
backup_label  global       pg_hba.conf.old       pg_log        pg_serial     pg_stat_tmp  pg_twophase  postgresql.conf
base          pg_clog      pg_hba.conf.original  pg_multixact  pg_snapshots  pg_subtrans  PG_VERSION   postgresql.conf.old
conf.d        pg_hba.conf  pg_ident.conf         pg_notify     pg_stat       pg_tblspc    pg_xlog

Restore transaction logs

Identify

Identify the location of the transaction log (xlog) archive for the database cluster.

If the RAID on the host serving the database is available, identify the xlog archive on it.

[enstore@dmsen03 ~]$ enstore config --show drivestat_server PITR_area
/srv3/enstore/pg_pitr
[enstore@dmsen03 pitr_restore_test1]$ ls -lh $(enstore config --show drivestat_server PITR_area)/pg_xlog_archive/drivestat | tail -2
-rw------- 1 enstore enstore 5.9K Aug 21 23:00 000000010000000A0000009B.xz
-rw------- 1 enstore enstore 6.9K Aug 21 23:30 000000010000000A0000009C.xz

As an alternative, if the RAID on the remote backup host is available, identify the xlog archive on it.

[enstore@dmsen03 ~]$ enstore config --show crons backup_dir
/srv3/enstore/backups
[enstore@dmsen03 ~]$ ls -lh $(enstore config --show crons backup_dir)/pg_xlog_archive/drivestat | tail -2
-rw------- 1 enstore enstore 5.9K Aug 21 23:00 000000010000000A0000009B.xz
-rw------- 1 enstore enstore 6.9K Aug 21 23:30 000000010000000A0000009C.xz

As a final alternative, if xlogs since the last base backup are available on tape only, copy all xlog-pack files since the last base backup from tape to disk. Since backup2Tape is scheduled to run once a day, there should typically only be up to one such xlog-pack file. Identify and extract it into an empty directory. Note that it's possible that no xlog-pack file had been written to tape yet since the last base backup.

[enstore@dmsen03 ~]$ ls -lh /pnfs/eagle/dmsen-backups/$(date +%Y/%m/%d)/*/*pg_xlog_pack-drivestat*
-rw-r--r-- 1 enstore enstore 3.6M Aug 21 08:02 /pnfs/eagle/dmsen-backups/2015/08/21/07/srv3-enstore-backups-pg_xlog_pack-drivestat-2015-08-21_08-02-41.tar
[enstore@dmsen03 ~]$ ENSTORE_CONFIG_HOST_REAL=$ENSTORE_CONFIG_HOST
[enstore@dmsen03 ~]$ enstore config --show crons backup2tape_config_host
conf-stken.fnal.gov
[enstore@dmsen03 ~]$ ENSTORE_CONFIG_HOST=$(enstore config --show crons backup2tape_config_host)
[enstore@dmsen03 ~]$ encp /pnfs/eagle/dmsen-backups/2015/08/21/07/srv3-enstore-backups-pg_xlog_pack-drivestat-2015-08-21_08-02-41.tar /tmp/
[enstore@dmsen03 ~]$ ls -lh /tmp/srv3-enstore-backups-pg_xlog_pack-drivestat-2015-08-21_08-02-41.tar
-rw-r--r-- 1 enstore enstore 3.6M Aug 22 09:36 /tmp/srv3-enstore-backups-pg_xlog_pack-drivestat-2015-08-21_08-02-41.tar
[enstore@dmsen03 ~]$ ENSTORE_CONFIG_HOST=$ENSTORE_CONFIG_HOST_REAL

[enstore@dmsen03 ~]$ mkdir /tmp/pitr_xlogs_test1
[enstore@dmsen03 ~]$ cd /tmp/pitr_xlogs_test1/
[enstore@dmsen03 ~]$ tar -xf /tmp/srv3-enstore-backups-pg_xlog_pack-drivestat-2015-08-21_08-02-41.tar -C /tmp/pitr_xlogs_test1/
[enstore@dmsen03 ~]$ ls -lh /tmp/pitr_xlogs_test1/ | tail -2
-rw------- 1 enstore enstore 6.2K Aug 21 07:30 000000010000000A0000007C.xz
-rw------- 1 enstore enstore 5.9K Aug 21 08:00 000000010000000A0000007D.xz

Restoration

Write a recovery.conf file in the data directory. It will be used by PostgreSQL to restore transaction logs since the base backup. It must be customized with an accessible location of the xlog archive.

[enstore@dmsen03 ~]$ cat /tmp/pitr_restore_test1/recovery.conf 
restore_command = 'unxz <"/srv3/enstore/pg_pitr/pg_xlog_archive/drivestat/%f.xz" >"%p"'

After the recovery is done, recovery.conf will be renamed by PostgreSQL to recovery.done. Also after the recovery is done, the latest pg_log file for the database cluster is likely to contain sh messages such as "00000002.history.xz: No such file or directory" and "00000001.history.xz: No such file or directory". These sh errors can be ignored.

Update cluster configuration

This section is relevant especially if the restoration is being performed as a test. Even if it's not a test, archive_command may still need customization in order for the transaction logs to be archived to an appropriate location. In this case, write or modify the configuration in the conf.d subdirectory of the data directory.

[enstore@dmsen03 ~]$ cat /tmp/pitr_restore_test1/conf.d/9_restore.conf 
port = 9912  # Non-conflicting with that of original instance
archive_command = '/bin/true'  # Effectively disables archiving, and prevents writing WAL into same directory

Settings contained in a file prefixed with "9_" should supersede all prior configuration settings, thereby preventing a conflict with the original database cluster instance.

Start database cluster

The database cluster can be started normally or by using pg_ctl.

[enstore@dmsen03 ~]$ pg_ctl start -D /tmp/pitr_restore_test1/
server starting
[enstore@dmsen03 ~]$ < 2015-08-22 12:16:35.772 CDT >LOG: redirecting log output to logging collector process
< 2015-08-22 12:16:35.772 CDT >HINT: Future log output will appear in directory "pg_log".