walmgr3 - Online in the Cloud

PROGRAM:

NAME

walmgr3 - tool for managing WAL-based replication for PostgreSQL.

SYNOPSIS

walmgr3 <config.ini> command [--not-really] [options]

DESCRIPTION

Walmgr3 is a tool to handle replication of PostgreSQL with PITR (also known as Log
Shipping).

This script allows to setup and administer the replication, it is also used by PostgreSQL
to archive and restore the WAL files.

See QUICK START below to start your first log shipping in few steps.

The command is one of the Master, Slave, Common or Internal commands listed below.

GENERAL OPTIONS

-V, --version
Print version info and exit.

-h, --help
Show this help message and exit.

-q, --quiet
Log only errors and warnings.

-v, --verbose
Log verbosely.

-d, --daemon
Run in daemon mode (go background).

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

SPECIFIC OPTIONS

--ini
Display sample ini file.

--set="param=val[,param=value]"
Override config setting

--init-master
Initialize Master walmgr3 configuration.

--init-slave
Initialize Slave walmgr3 configuration.

--config-dir=filepath
Configuration file location for --init-X commands.

--slave=hostname
Slave host name.

--pgdata=path
PostgreSQL data directory.

--ssh-keygen
Generate a SSH key pair if needed (used in Master).

--ssh-add-key=keyfile.pub
Add the public key file to authorized_hosts file (used in Slave).

--ssh-remove-key=ssh_key
Remove Master ssh key from authorized_hosts file (used in Slave).

--primary-conninfo=connection_string
Provide the connection string to the streaming replication Master (used in Slave).

--add-password=plaintext_file
Add password for streaming replication from plain text file to .pgpass. Additional
fields for password file entry will be extracted from primary-conninfo (used in
Slave).

--remove-password
Remove .pgpass entry, which was used for streaming replication (used in Slave)

--synch-standby=synchronous_standby_names
Do the same thing as command synch-standby, but walmgr ini file is not used. This
option can be used when walmgr ini is not available. It tries to guess the postgres
config location, --pgdata option may also be needed. (used in Master)

DAEMON OPTIONS

-r, --reload
Reload config (send SIGHUP).

-s, --stop
Stop program safely (send SIGINT).

-k, --kill
Kill program immediately (send SIGTERM).

MASTER COMMANDS

setup
Sets up PostgreSQL for WAL archiving, creates necessary directory structures on Slave.

sync
Copies 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 configuration 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
Stop archiving and de-configure PostgreSQL archiving.

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

synch-standby
Enables/disables synchronous streaming replication for given application name(s). Does
additional check before enabling synchronous mode.

SLAVE COMMANDS

boot
Stop WAL playback and bring the database up so it can accept queries.

pause
Pauses WAL playback.

continue
Continues previously paused WAL playback.

createslave
Creates backup from Master database using streaming replication. Also creates
recovery.conf and starts slave standby. Backup is created with pg_basebackup and
pg_receivexlog (available in 9.2 and up).

COMMON COMMANDS

listbackups
Lists available backups 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 not 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.

EXPERIMENTAL: If run on Slave, creates backup from in-recovery Slave data. WAL playback is
paused, Slave data directory is backed up to full_backup directory and WAL playback is
resumed. Backups are rotated as needed. The idea is to move the backup load away from
production node. Usable from PostgreSQL 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 moved). Alternative destination
directory can be specified with dst.

cleanup
Cleanup any walmgr3 files after stop.

INTERNAL COMMANDS

xarchive <srcpath> <srcname>
On Master, archive one WAL file.

xrestore <srcname> <dstpath> [last restartpoint wal]
On Slave, restore one WAL file.

xlock
On Master, create lock file to deny other concurrent backups.

xrelease
On Slave, remove backup lock file, allow other backup to run.

xrotate
Rotate backups by increasing backup directory suffixes. Note that since we also have to
make room for next backup, we actually have keep_backups - 1 backups available after this.

Unneeded WAL files are not removed here, it is handled by xpurgewals command instead.

xpurgewals
On Slave, remove WAL files not needed for recovery.

xpartialsync <filename> <offset> <bytes>
Read bytes worth of data from stdin, append to the partial WAl file starting from offset.
On error it is assumed that master restarts from zero.

The resulting file is always padded to XLOG_SEGMENT_SIZE bytes to simplify recovery.

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 walmgr3.

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
Optional. Slave directory where configuration file backups are stored.

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. It reduces network traffic at the
cost of extra CPU time.

keep_symlinks
Keep symlinks for pg_xlog and pg_log.

hot_standby
If set to 1, walmgr3 setup will set wal_level to hot_standby (PostgreSQL 9.0 and
newer).

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

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

Sample master.ini
[walmgr]
job_name = wal-master
logfile = ~/log/%(job_name)s.log
pidfile = ~/pid/%(job_name)s.pid
use_skylog = 1

master_db = dbname=my_db
master_data = /var/lib/postgresql/9.1/main
master_config = /etc/postgresql/9.1/main/postgresql.conf
master_bin = /usr/lib/postgresql/9.1/bin

# set this only if you can afford database restarts during setup and stop.
#master_restart_cmd = /etc/init.d/postgresql-9.1 restart

slave = slave-host
slave_config = /var/lib/postgresql/conf/wal-slave.ini

walmgr_data = /var/lib/postgresql/walshipping
completed_wals = %(walmgr_data)s/logs.complete
partial_wals = %(walmgr_data)s/logs.partial
full_backup = %(walmgr_data)s/data.master
config_backup = %(walmgr_data)s/config.backup

# syncdaemon update frequency
loop_delay = 10.0
# use record based shipping available since 8.2
use_xlog_functions = 0

# pass -z to rsync, useful on low bandwidth links
compression = 0

# keep symlinks for pg_xlog and pg_log
keep_symlinks = 1

# tell walmgr to set wal_level to hot_standby during setup
#hot_standby = 1

# periodic sync
#command_interval = 600
#periodic_command = /var/lib/postgresql/walshipping/periodic.sh

Slave settings
slave_data
PostgreSQL data directory for the Slave. This is where the restored backup is
copied/moved.

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

slave_stop_cmd
Script to stop PostgreSQL on Slave.

slave_start_cmd
Script to start PostgreSQL on Slave.

slave_config_dir
Directory for PostgreSQL configuration files. If specified, walmgr3 restore attempts
to restore configuration files from config_backup directory.

slave_pg_xlog
Set to the directory on the Slave where pg_xlog files get written to. On a restore to
the Slave walmgr3 will create a symbolic link from data/pg_xlog to this location.

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.

config_backup
Optional. Slave directory where configuration file backups are stored.

backup_datadir
Set backup_datadir to no to prevent walmgr3 from making a backup of the data directory
when restoring to the Slave. This defaults to yes.

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.

primary_conninfo
Primary database connection string for hot standby - enabling this will cause the
Slave to be started in hot standby mode.

Sample slave.ini
[walmgr]
job_name = wal-slave
logfile = ~/log/%(job_name)s.log
use_skylog = 1

slave_data = /var/lib/postgresql/9.1/main
slave_bin = /usr/lib/postgresql/9.1/bin
slave_stop_cmd = /etc/init.d/postgresql-9.1 stop
slave_start_cmd = /etc/init.d/postgresql-9.1 start
slave_config_dir = /etc/postgresql/9.1/main

# alternative pg_xlog directory for slave, symlinked to pg_xlog on restore
#slave_pg_xlog = /vol2/pg_xlog

walmgr_data = ~/walshipping
completed_wals = %(walmgr_data)s/logs.complete
partial_wals = %(walmgr_data)s/logs.partial
full_backup = %(walmgr_data)s/data.master
config_backup = %(walmgr_data)s/config.backup

backup_datadir = yes
keep_backups = 0
archive_command =

# primary database connect string for hot standby -- enabling
# this will cause the slave to be started in hot standby mode.
#primary_conninfo = host=master port=5432 user=postgres

EXIT STATUS

0
Successful program execution.

ENVIRONMENT

PostgreSQL environment variables can be used.

QUICK START

1. Set up passwordless ssh-key on Master and write configuration file

master$ walmgr3 --ssh-keygen --init-master --slave <slave_hostname>

2. Set up passwordless ssh authentication from Master to Slave and write configuration
file on Slave

slave$ walmgr3 --init-slave --ssh-add-key=/tmp/id_rsa.pub

3. Logging setup on Master and Slave

master$ cp skylog.ini ~postgres/
slave$ cp skylog.ini ~postgres/

4. Start archival process and create a base backup

master$ walmgr3 /var/lib/postgresql/conf/wal-master.ini setup
master$ walmgr3 /var/lib/postgresql/conf/wal-master.ini backup

CAUTION: 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.

5. Prepare postgresql.conf and pg_hba.conf on Slave and start replay

slave$ walmgr3 /var/lib/postgresql/conf/wal-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.

'walmgr3 restore' moves data in place, creates recovery.conf and
starts postmaster in recovery mode.

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

master$ walmgr3 /var/lib/postgresql/conf/wal-master.ini sync

7. If need to stop replay on Slave and boot into normal mode, do:

slave$ walmgr3 /var/lib/postgresql/conf/wal-slave.ini boot

01/15/2016 WALMGR3(1)

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