Ubuntu Manpage: walmgr - tools for managing WAL-based replication for PostgreSQL.

NAME

       walmgr - tools for managing WAL-based replication for PostgreSQL.

SYNOPSIS

       walmgr.py <config.ini> command

DESCRIPTION

       It is both admin and worker script for PostgreSQL PITR replication.

QUICK START

1. Set up passwordless ssh authentication from master to slave

master$ test -f ~/.ssh/id_dsa.pub || ssh-keygen -t dsa
master$ cat ~/.ssh/id_dsa.pub | ssh slave cat \>\> .ssh/authorized_keys

2. Configure paths

master$ edit master.ini
slave$ edit slave.ini

Make sure that walmgr.py executable has same pathname on slave and master.

3. Start archival process and create a base backup

master$ ./walmgr.py master.ini setup
master$ ./walmgr.py master.ini backup

Note: starting from PostgreSQL 8.3 the archiving is enabled by setting
archive_mode GUC to on. However changing this parameter requires the
server to be restarted.

4. Prepare postgresql.conf and pg_hba.conf on slave and start replay

master$ scp $PGDATA/*.conf slave:
slave$ ./walmgr.py slave.ini restore

For debian based distributions the standard configuration files are located
in /etc/postgresql/x.x/main directory. If another scheme is used the postgresql.conf
and pg_hba.conf should be copied to slave full_backup directory. Make sure to
disable archive_command in slave config.

'walmgr.py restore' moves data in place, creates recovery.conf and starts postmaster
in recovery mode.

5. In-progress WAL segments can be backup by command:

master$ ./walmgr.py master.ini sync

6. If need to stop replay on slave and boot into normal mode, do:

slave$ ./walmgr.py slave.ini boot

GENERAL OPTIONS

       Common options to all walmgr.py commands.

       -h, --help
           show this help message and exit

       -q, --quiet
           make program silent

       -v, --verbose
           make program more verbose

       -n, --not-really
           Show what would be done without actually doing anything.

MASTER COMMANDS

   setup
       Sets up postgres archiving, creates necessary directory structures on slave.

   sync
       Synchronizes in-progress WAL files to slave.

   syncdaemon
       Start WAL synchronization in daemon mode. This will start periodically synching the in-progress WAL files
       to slave.

       The following parameters are used to drive the syncdaemon: loop_delay - how long to sleep between the
       synchs. use_xlog_functions - use record based shipping to synchronize in-progress WAL segments.

   stop
       Deconfigures postgres archiving.

   periodic
       Runs periodic command, if configured. This enables to execute arbitrary commands on interval, useful for
       synchronizing scripts, config files, crontabs etc.

   listbackups
       List backup sets available on slave node.

   backup
       Creates a new base backup from master database. Will purge expired backups and WAL files on slave if
       keep_backups is specified. During a backup a lock file is created in slave completed_wals directory. This
       is to prevent simultaneous backups and resulting corruption. If running backup is terminated, the
       BACKUPLOCK file may have to be removed manually.

   restore <set> <dst>
       EXPERIMENTAL. Attempts to restore the backup from slave to master.

SLAVE COMMANDS

   boot
       Stop log playback and bring the database up.

   pause
       Pauses WAL playback.

   continue
       Continues previously paused WAL playback.

   listbackups
       Lists available backups.

   backup
       EXPERIMENTAL. Creates a new backup from slave data. Log replay is paused, slave data directory is backed
       up to full_backup directory and log replay resumed. Backups are rotated as needed. The idea is to move
       the backup load away from production node. Usable from postgres 8.2 and up.

   restore [src][dst]
       Restores the specified backup set to target directory. If specified without arguments the latest backup
       is moved to slave data directory (doesn’t obey retention rules). If src backup is specified the backup is
       copied (instead of moving). Alternative destination directory can be specified with dst.

CONFIGURATION

Common settings
job_name

Optional. Indentifies this script, used in logging. Keep unique if using central logging.

logfile

Where to log.

use_skylog

Optional. If nonzero, skylog.ini is used for log configuration.

Master settings
pidfile

Pid file location for syncdaemon mode (if running with -d). Otherwise not required.

master_db

Database to connect to for pg_start_backup() etc. It is not a good idea to use dbname=template if
running syncdaemon in record shipping mode.

master_data

Master data directory location.

master_config

Master postgresql.conf file location. This is where archive_command gets updated.

master_restart_cmd

The command to restart master database, this used after changing archive_mode parameter. Leave unset,
if you cannot afford to restart the database at setup/stop.

slave

Slave host and base directory.

slave_config

Configuration file location for the slave walmgr.

completed_wals

Slave directory where archived WAL files are copied.

partial_wals

Slave directory where incomplete WAL files are stored.

full_backup

Slave directory where full backups are stored.

config_backup

Slave directory where configuration file backups are stored. Optional.

loop_delay

The frequency of syncdaemon updates. In record shipping mode only incremental updates are sent, so
smaller interval can be used.

use_xlog_functions

Use pg_xlog functions for record based shipping (available in 8.2 and up).

compression

If nonzero, a -z flag is added to rsync cmdline. Will reduce network traffic at the cost of extra CPU
time.

periodic_command

Shell script to be executed at specified time interval. Can be used for synchronizing scripts, config
files etc.

command_interval

How ofter to run periodic command script. In seconds, and only evaluated at log switch times.

hot_standby ===

Boolean. If set to true, walmgr setup will set wal_level to hot_standby (9.0 and newer).

Sample master.ini
[wal-master]
logfile = master.log
pidfile = master.pid
master_db = dbname=template1
master_data = /var/lib/postgresql/8.0/main
master_config = /etc/postgresql/8.0/main/postgresql.conf
slave = slave:/var/lib/postgresql/walshipping
completed_wals = %(slave)s/logs.complete
partial_wals = %(slave)s/logs.partial
full_backup = %(slave)s/data.master
loop_delay = 10.0
use_xlog_functions = 1
compression = 1

Slave settings
slave_data

Postgres data directory for the slave. This is where the restored backup is copied/moved.

slave_config_dir

Directory for postgres configuration files. If specified, "walmgr restore" attempts to restore
configuration files from config_backup directory.

slave_stop_cmd

Script to stop postmaster on slave.

slave_start_cmd

Script to start postmaster on slave.

slave

Base directory for slave files (logs.complete, data.master etc)

slave_bin

Specifies the location of postgres binaries (pg_controldata, etc). Needed if they are not already in
the PATH.

completed_wals

Directory where complete WAL files are stored. Also miscellaneous control files are created in this
directory (BACKUPLOCK, STOP, PAUSE, etc.).

partial_wals

Directory where partial WAL files are stored.

full_backup

Directory where full backups are stored.

keep_backups

Number of backups to keep. Also all WAL files needed to bring earliest

backup up to date are kept. The backups are rotated before new backup is started, so at one point
there is actually one less backup available.

It probably doesn’t make sense to specify keep_backups if periodic backups are not performed - the
WAL files will pile up quickly.

Backups will be named data.master, data.master.0, data.master.1 etc.

archive_command

Script to execute before rotating away the oldest backup. If it fails backups will not be rotated.

slave_pg_xlog

Set slave_pg_xlog to the directory on the slave where pg_xlog files get written to. On a restore to
the slave walmgr.py will create a symbolic link from data/pg_xlog to this location.

backup_datadir

Set backup_datadir to no to prevent walmgr.py from making a backup of the data directory when
restoring to the slave. This defaults to yes

Sample slave.ini
[wal-slave]
logfile = slave.log
slave_data = /var/lib/postgresql/8.0/main
slave_stop_cmd = /etc/init.d/postgresql-8.0 stop
slave_start_cmd = /etc/init.d/postgresql-8.0 start
slave = /var/lib/postgresql/walshipping
completed_wals = %(slave)s/logs.complete
partial_wals = %(slave)s/logs.partial
full_backup = %(slave)s/data.master
keep_backups = 5
backup_datadir = yes

03/13/2012 WALMGR(1)