pgpool-II 4.1.23 Documentation
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8.3. Pgpool-II + Watchdog Setup Example

This section shows an example of streaming replication configuration using Pgpool-II. In this example, we use 3 Pgpool-II servers to manage PostgreSQL servers to create a robust cluster system and avoid the single point of failure or split brain.

PostgreSQL 11 is used in this configuration example, all scripts have also been tested with PostgreSQL 12.

8.3.1. Requirements

We assume that all the Pgpool-II servers and the PostgreSQL servers are in the same subnet.

8.3.2. Cluster System Configuration

We use 3 servers with CentOS 7.4. Let these servers be server1, server2, server3. We install PostgreSQL and Pgpool-II on each server.

Figure 8-1. Cluster System Configuration

Note: The roles of Active, Standy, Primary, Standby are not fixed and may be changed by further operations.

Table 8-2. Hostname and IP address

Hostname	IP Address	Virtual IP
server1	192.168.137.101	192.168.137.150
server2	192.168.137.102
server3	192.168.137.103

Table 8-3. PostgreSQL version and Configuration

Item	Value	Detail
PostgreSQL Version	11.1	-
port	5432	-
$PGDATA	/var/lib/pgsql/11/data	-
Archive mode	on	/var/lib/pgsql/archivedir
Replication Slots	Enable	-
Start automatically	Disable	-

Table 8-4. Pgpool-II version and Configuration

Item	Value	Detail
Pgpool-II Version	4.1.0	-
port	9999	Pgpool-II accepts connections
	9898	PCP process accepts connections
	9000	watchdog accepts connections
	9694	UDP port for receiving Watchdog's heartbeat signal
Config file	/etc/pgpool-II/pgpool.conf	Pgpool-II config file
Pgpool-II start user	postgres (Pgpool-II 4.1 or later)	Pgpool-II 4.0 or before, the default startup user is root
Running mode	streaming replication mode	-
Watchdog	on	Life check method: heartbeat
Start automatically	Disable	-

8.3.3. Installation

In this example, we install Pgpool-II and PostgreSQL RPM packages with YUM.

Install PostgreSQL by using PostgreSQL YUM repository.

[all servers]# yum install -y https://download.postgresql.org/pub/repos/yum/reporpms/EL-7-x86_64/pgdg-redhat-repo-latest.noarch.rpm
[all servers]# yum install -y postgresql11-server

Since Pgpool-II related packages are also included in PostgreSQL YUM repository, add the "exclude" settings to /etc/yum.repos.d/pgdg-redhat-all.repo so that Pgpool-II is not installed from PostgreSQL YUM repository.

[all servers]# vi /etc/yum.repos.d/pgdg-redhat-all.repo

The following is a setting example of /etc/yum.repos.d/pgdg-redhat-all.repo.

[pgdg-common]
...
exclude=pgpool*

[pgdg14]
...
exclude=pgpool*

[pgdg13]
...
exclude=pgpool*

[pgdg12]
...
exclude=pgpool*

[pgdg11]
...
exclude=pgpool*

[pgdg10]
...
exclude=pgpool*

[pgdg96]
...
exclude=pgpool*

Install Pgpool-II from Pgpool-II YUM repository.

[all servers]# yum install -y http://www.pgpool.net/yum/rpms/4.1/redhat/rhel-7-x86_64/pgpool-II-release-4.1-3.noarch.rpm
[all servers]# yum install -y pgpool-II-pg11-*

8.3.4. Before Starting

Before you start the configuration process, please check the following prerequisites.

Set up PostgreSQL streaming replication on the primary server. In this example, we use WAL archiving.
First, we create the directory /var/lib/pgsql/archivedir to store WAL segments on all servers. In this example, only Primary node archives WAL locally.
```
[all servers]# su - postgres
[all servers]$ mkdir /var/lib/pgsql/archivedir
    
```
Initialize PostgreSQL on the primary server.
```
[server1]# su - postgres
[server1]$ /usr/pgsql-11/bin/initdb -D $PGDATA
    
```
Then we edit the configuration file $PGDATA/postgresql.conf on server1 (primary) as follows. Enable wal_log_hints to use pg_rewind. Since the Primary may become a Standby later, we set hot_standby = on.
```
listen_addresses = '*'
archive_mode = on
archive_command = 'cp "%p" "/var/lib/pgsql/archivedir/%f"'
max_wal_senders = 10
max_replication_slots = 10
wal_level = replica
hot_standby = on
wal_log_hints = on
    
```
We use the online recovery functionality of Pgpool-II to setup standby server after the primary server is started.
Because of the security reasons, we create a user repl solely used for replication purpose, and a user pgpool for streaming replication delay check and health check of Pgpool-II.
Table 8-5. Users
User Name Password Detail
repl repl PostgreSQL replication user
pgpool pgpool Pgpool-II health check and replication delay check user
postgres postgres User running online recovery
```
[server1]# psql -U postgres -p 5432
postgres=# SET password_encryption = 'scram-sha-256';
postgres=# CREATE ROLE pgpool WITH LOGIN;
postgres=# CREATE ROLE repl WITH REPLICATION LOGIN;
postgres=# \password pgpool
postgres=# \password repl
postgres=# \password postgres
    
```
If you want to show "replication_state" and "replication_sync_state" column in SHOW POOL NODES command result, role pgpool needs to be PostgreSQL super user or or in pg_monitor group (Pgpool-II 4.1 or later). Grant pg_monitor to pgpool:
```
GRANT pg_monitor TO pgpool;
    
```
Note: If you plan to use detach_false_primary(Pgpool-II 4.0 or later), role "pgpool" needs to be PostgreSQL super user or or in "pg_monitor" group to use this feature.
Assuming that all the Pgpool-II servers and the PostgreSQL servers are in the same subnet and edit pg_hba.conf to enable scram-sha-256 authentication method.
```
host    all             all             samenet                 scram-sha-256
host    replication     all             samenet                 scram-sha-256
    
```
To use the automated failover and online recovery of Pgpool-II, it is required to allow SSH public key authentication (passwordless SSH login) to all backend servers as Pgpool-II startup user (default is postgres. Pgpool-II 4.0 or before, default is root) and PostgreSQL startup user (default is postgres).
First, set postgres user's passwrod.
```
[all servers]# passwd postgres
    
```
Execute the following command on all servers to set up passwordless SSH. In this example, we assume that the generated key file name is id_rsa_pgpool.
```
[all servers]# mkdir ~/.ssh
[all servers]# chmod 700 ~/.ssh
[all servers]# cd ~/.ssh
[all servers]# ssh-keygen -t rsa -f id_rsa_pgpool
[all servers]# ssh-copy-id -i id_rsa_pgpool.pub postgres@server1
[all servers]# ssh-copy-id -i id_rsa_pgpool.pub postgres@server2
[all servers]# ssh-copy-id -i id_rsa_pgpool.pub postgres@server3

[all servers]# su - postgres
[all servers]$ mkdir ~/.ssh
[all servers]$ chmod 700 ~/.ssh
[all servers]$ cd ~/.ssh
[all servers]$ ssh-keygen -t rsa -f id_rsa_pgpool
[all servers]$ ssh-copy-id -i id_rsa_pgpool.pub postgres@server1
[all servers]$ ssh-copy-id -i id_rsa_pgpool.pub postgres@server2
[all servers]$ ssh-copy-id -i id_rsa_pgpool.pub postgres@server3
    
```
After setting SSH, make sure that you can run ssh postgres@serverX -i ~/.ssh/id_rsa_pgpool command as Pgpool-II startup user and PostgreSQL startup user to log in without entering a password.
Note: If you failed to login using SSH public key authentication, please check the following:
- Ensure the public key authentication option PubkeyAuthentication are allowed in /etc/ssh/sshd_config:
```
PubkeyAuthentication yes
      
```
- if the password authentication is disabled, you can fail to run ssh-copy-id, temporarily add the following configuration in /etc/ssh/sshd_config.
```
PasswordAuthentication yes
      
```
- If SELinux is enabled, SSH public key authentication (passwordless SSH) may fail. You need to run the following command on all servers.
```
[all servers]# su - postgres
[all servers]$ restorecon -Rv ~/.ssh
      
```

User Name	Password	Detail
repl	repl	PostgreSQL replication user
pgpool	pgpool	Pgpool-II health check and replication delay check user
postgres	postgres	User running online recovery

To allow repl user without specifying password for streaming replication and online recovery, and execute pg_rewind using postgres, we create the .pgpass file in postgres user's home directory and change the permission to 600 on each PostgreSQL server.

[all servers]# su - postgres
[all servers]$ vi /var/lib/pgsql/.pgpass
server1:5432:replication:repl:<repl user password>
server2:5432:replication:repl:<repl user password>
server3:5432:replication:repl:<repl user password>
server1:5432:postgres:postgres:<postgres user password>
server2:5432:postgres:postgres:<postgres user password>
server3:5432:postgres:postgres:<postgres user password>
[all servers]$ chmod 600  /var/lib/pgsql/.pgpass

When connect to Pgpool-II and PostgreSQL servers, the target port must be accessible by enabling firewall management softwares. Following is an example for CentOS/RHEL7.

[all servers]# firewall-cmd --permanent --zone=public --add-service=postgresql
[all servers]# firewall-cmd --permanent --zone=public --add-port=9999/tcp --add-port=9898/tcp --add-port=9000/tcp --add-port=9694/udp
[all servers]# firewall-cmd --reload

8.3.5. Pgpool-II Configuration

8.3.5.1. Common Settings

Here are the common settings on server1, server2 and server3.

When installing Pgpool-II from RPM, all the Pgpool-II configuration files are in /etc/pgpool-II. In this example, we copy the sample configuration file for streaming replication mode.

# cp -p /etc/pgpool-II/pgpool.conf.sample-stream /etc/pgpool-II/pgpool.conf

To allow Pgpool-II and PCP to accept all incoming connections, we set listen_addresses = '*'.

listen_addresses = '*'
pcp_listen_addresses = '*'

Specify replication delay check user and password. In this example, we leave sr_check_user empty, and create the entry in pool_passwd. From Pgpool-II 4.0, if these parameters are left blank, Pgpool-II will first try to get the password for that specific user from sr_check_password file before using the empty password.

sr_check_user = 'pgpool'
sr_check_password = ''

Enable health check so that Pgpool-II performs failover. Also, if the network is unstable, the health check fails even though the backend is running properly, failover or degenerate operation may occur. In order to prevent such incorrect detection of health check, we set health_check_max_retries = 3. Specify health_check_user and health_check_password in the same way like sr_check_user and sr_check_password.

health_check_period = 5
                                            # Health check period
                                            # Disabled (0) by default
health_check_timeout = 30
                                            # Health check timeout
                                            # 0 means no timeout
health_check_user = 'pgpool'
health_check_password = ''

health_check_max_retries = 3

Specify the PostgreSQL backend information. Multiple backends can be specified by adding a number at the end of the parameter name.

# - Backend Connection Settings -

backend_hostname0 = 'server1'
                                            # Host name or IP address to connect to for backend 0
backend_port0 = 5432
                                            # Port number for backend 0
backend_weight0 = 1
                                            # Weight for backend 0 (only in load balancing mode)
backend_data_directory0 = '/var/lib/pgsql/11/data'
                                            # Data directory for backend 0
backend_flag0 = 'ALLOW_TO_FAILOVER'
                                            # Controls various backend behavior
                                            # ALLOW_TO_FAILOVER or DISALLOW_TO_FAILOVER
backend_hostname1 = 'server2'
backend_port1 = 5432
backend_weight1 = 1
backend_data_directory1 = '/var/lib/pgsql/11/data'
backend_flag1 = 'ALLOW_TO_FAILOVER'

backend_hostname2 = 'server3'
backend_port2 = 5432
backend_weight2 = 1
backend_data_directory2 = '/var/lib/pgsql/11/data'
backend_flag2 = 'ALLOW_TO_FAILOVER'

To show "replication_state" and "replication_sync_state" column in SHOW POOL NODES command result, backend_application_name parameter is required. Here we specify each backend's hostname in these parameters. (Pgpool-II 4.1 or later)

...
backend_application_name0 = 'server1'
...
backend_application_name1 = 'server2'
...
backend_application_name2 = 'server3'

8.3.5.2. Failover configuration

Specify failover.sh script to be executed after failover in failover_command parameter. If we use 3 PostgreSQL servers, we need to specify follow_master_command to run after failover on the primary node failover. In case of two PostgreSQL servers, follow_master_command setting is not necessary.

Pgpool-II replaces the following special characters with the backend specific information while executing the scripts. See failover_command for more details about each character.

failover_command = '/etc/pgpool-II/failover.sh %d %h %p %D %m %H %M %P %r %R %N %S'
follow_master_command = '/etc/pgpool-II/follow_master.sh %d %h %p %D %m %H %M %P %r %R'

Note: %N and %S are added in Pgpool-II 4.1. Please note that these characters cannot be specified if using Pgpool-II 4.0 or earlier.

Sample scripts failover.sh and follow_master.sh are installed in /etc/pgpool-II/. Create failover scripts using these sample files.

[all servers]# cp -p /etc/pgpool-II/failover.sh{.sample,}
[all servers]# cp -p /etc/pgpool-II/follow_master.sh{.sample,}
[all servers]# chown postgres:postgres /etc/pgpool-II/{failover.sh,follow_master.sh}

Basically, it should work if you change PGHOME according to PostgreSQL installation directory.

[server1]# vi /etc/pgpool-II/failover.sh
...
PGHOME=/usr/pgsql-11
...

[server1]# vi /etc/pgpool-II/follow_master.sh
...
PGHOME=/usr/pgsql-11
...

Since user authentication is required to use the PCP command in follow_master_command script, we need to specify user name and md5 encrypted password in pcp.conf in format "username:encrypted password".

if pgpool user is specified in PCP_USER in follow_master.sh,

# cat /etc/pgpool-II/follow_master.sh
...
PCP_USER=pgpool
...

then we use pg_md5 to create the encrypted password entry for pgpool user as below:

[all servers]# echo 'pgpool:'`pg_md5 PCP passowrd` >> /etc/pgpool-II/pcp.conf

Since follow_master.sh script must execute PCP command without entering a password, we need to create .pcppass in the home directory of Pgpool-II startup user (postgres user) on each server.

[all servers]# su - postgres
[all servers]$ echo 'localhost:9898:pgpool:<pgpool user password>' > ~/.pcppass
[all servers]$ chmod 600 ~/.pcppass

Note: The follow_master.sh script does not support tablespaces. If you are using tablespaces, you need to modify the script to support tablespaces.

8.3.5.3. Pgpool-II Online Recovery Configurations

Next, in order to perform online recovery with Pgpool-II we specify the PostgreSQL user name and online recovery command recovery_1st_stage. Because Superuser privilege in PostgreSQL is required for performing online recovery, we specify postgres user in recovery_user. Then, we create recovery_1st_stage and pgpool_remote_start in database cluster directory of PostgreSQL primary server (server1), and add execute permission.

recovery_user = 'postgres'
                                            # Online recovery user
recovery_password = ''
                                            # Online recovery password

recovery_1st_stage_command = 'recovery_1st_stage'

Online recovery sample scriptsrecovery_1st_stage and pgpool_remote_start are installed in /etc/pgpool-II/. Copy these files to the data directory of the primary server (server1).

[server1]# cp -p /etc/pgpool-II/recovery_1st_stage.sample /var/lib/pgsql/11/data/recovery_1st_stage
[server1]# cp -p /etc/pgpool-II/pgpool_remote_start.sample /var/lib/pgsql/13/data/pgpool_remote_start
[server1]# chown postgres:postgres /var/lib/pgsql/11/data/{recovery_1st_stage,pgpool_remote_start}

Basically, it should work if you change PGHOME according to PostgreSQL installation directory.

[server1]# vi /var/lib/pgsql/11/data/recovery_1st_stage
...
PGHOME=/usr/pgsql-11
...

[server1]# vi /var/lib/pgsql/11/data/pgpool_remote_start
...
PGHOME=/usr/pgsql-11
...

In order to use the online recovery functionality, the functions of pgpool_recovery, pgpool_remote_start, pgpool_switch_xlog are required, so we need install pgpool_recovery on template1 of PostgreSQL server server1.

[server1]# su - postgres
[server1]$ psql template1 -c "CREATE EXTENSION pgpool_recovery"

Note: The recovery_1st_stage script does not support tablespaces. If you are using tablespaces, you need to modify the script to support tablespaces.

8.3.5.4. Client Authentication Configuration

Because in the section Before Starting, we already set PostgreSQL authentication method to scram-sha-256, it is necessary to set a client authentication by Pgpool-II to connect to backend nodes. When installing with RPM, the Pgpool-II configuration file pool_hba.conf is in /etc/pgpool-II. By default, pool_hba authentication is disabled, set enable_pool_hba = on to enable it.

enable_pool_hba = on

The format of pool_hba.conf file follows very closely PostgreSQL's pg_hba.conf format. Set pgpool and postgres user's authentication method to scram-sha-256.

host    all         pgpool           0.0.0.0/0          scram-sha-256
host    all         postgres         0.0.0.0/0          scram-sha-256

Note: Please note that in Pgpool-II 4.0 only AES encrypted password or clear text password can be specified in health_check_password, sr_check_password, wd_lifecheck_password, recovery_password in pgpool.conf.

The default password file name for authentication is pool_passwd. To use scram-sha-256 authentication, the decryption key to decrypt the passwords is required. We create the .pgpoolkey file in Pgpool-II start user postgres's (Pgpool-II 4.1 or later) home directory. (Pgpool-II 4.0 or before, by default Pgpool-II is started as root)

[all servers]# su - postgres
[all servers]$ echo 'some string' > ~/.pgpoolkey
[all servers]$ chmod 600 ~/.pgpoolkey

Execute command pg_enc -m -k /path/to/.pgpoolkey -u username -p to register user name and AES encrypted password in file pool_passwd. If pool_passwd doesn't exist yet, it will be created in the same directory as pgpool.conf.

[all servers]# su - postgres
[all servers]$ pg_enc -m -k ~/.pgpoolkey -u pgpool -p
db password: [pgpool user's password]
[all servers]$ pg_enc -m -k ~/.pgpoolkey -u postgres -p
db password: [postgres user's passowrd]

# cat /etc/pgpool-II/pool_passwd 
pgpool:AESheq2ZMZjynddMWk5sKP/Rw==
postgres:AESHs/pWL5rtXy2IwuzroHfqg==

8.3.5.5. Watchdog Configuration

Enable watchdog functionality on server1, server2, server3.

use_watchdog = on

Specify virtual IP address that accepts connections from clients on server1, server2, server3. Ensure that the IP address set to virtual IP isn't used yet.

delegate_IP = '192.168.137.150'

To bring up/down the virtual IP and send the ARP requests, we set if_up_cmd, if_down_cmd and arping_cmd. The network interface used in this example is "enp0s8". Since root privilege is required to execute if_up/down_cmd or arping_cmd command, use setuid on these command or allow Pgpool-II startup user, postgres user (Pgpool-II 4.1 or later) to run sudo command without a password.

Note: If Pgpool-II is installed using RPM, the postgres user has been configured to run ip/arping via sudo without a password.
postgres ALL=NOPASSWD: /sbin/ip
postgres ALL=NOPASSWD: /usr/sbin/arping
    

Here we configure the following parameters to run if_up/down_cmd or arping_cmd with sudo.

if_up_cmd = '/usr/bin/sudo /sbin/ip addr add $_IP_$/24 dev enp0s8 label enp0s8:0'
if_down_cmd = '/usr/bin/sudo /sbin/ip addr del $_IP_$/24 dev enp0s8'
arping_cmd = '/usr/bin/sudo /usr/sbin/arping -U $_IP_$ -w 1 -I enp0s8'

Note: If "Defaults requiretty" is set in the /etc/sudoers, please ensure that the pgpool startup user can execute the if_up_cmd, if_down_cmd and arping_cmd command without a tty.

Set if_cmd_path and arping_path according to the command path. If if_up/down_cmd or arping_cmd starts with "/", these parameters will be ignored.

if_cmd_path = '/sbin'
arping_path = '/usr/sbin'

Specify the hostname and port number of each Pgpool-II server.

server1

wd_hostname = 'server1'
wd_port = 9000

server2

wd_hostname = 'server2'
wd_port = 9000

server3

wd_hostname = 'server3'
wd_port = 9000

Specify the hostname, Pgpool-II port number, and watchdog port number of monitored Pgpool-II servers on each Pgpool-II server.

server1

# - Other pgpool Connection Settings -

other_pgpool_hostname0 = 'server2'
                                            # Host name or IP address to connect to for other pgpool 0
                                            # (change requires restart)
other_pgpool_port0 = 9999
                                            # Port number for other pgpool 0
                                            # (change requires restart)
other_wd_port0 = 9000
                                            # Port number for other watchdog 0
                                            # (change requires restart)
other_pgpool_hostname1 = 'server3'
other_pgpool_port1 = 9999
other_wd_port1 = 9000

server2

# - Other pgpool Connection Settings -

other_pgpool_hostname0 = 'server1'
                                            # Host name or IP address to connect to for other pgpool 0
                                            # (change requires restart)
other_pgpool_port0 = 9999
                                            # Port number for other pgpool 0
                                            # (change requires restart)
other_wd_port0 = 9000
                                            # Port number for other watchdog 0
                                            # (change requires restart)
other_pgpool_hostname1 = 'server3'
other_pgpool_port1 = 9999
other_wd_port1 = 9000

server3

# - Other pgpool Connection Settings -

other_pgpool_hostname0 = 'server1'
                                            # Host name or IP address to connect to for other pgpool 0
                                            # (change requires restart)
other_pgpool_port0 = 9999
                                            # Port number for other pgpool 0
                                            # (change requires restart)
other_wd_port0 = 9000
                                            # Port number for other watchdog 0
                                            # (change requires restart)
other_pgpool_hostname1 = 'server2'
other_pgpool_port1 = 9999
other_wd_port1 = 9000

Specify the hostname and port number of destination for sending heartbeat signal on server1, server2, server3.

server1

heartbeat_destination0 = 'server2'
                                            # Host name or IP address of destination 0
                                            # for sending heartbeat signal.
                                            # (change requires restart)
heartbeat_destination_port0 = 9694
                                            # Port number of destination 0 for sending
                                            # heartbeat signal. Usually this is the
                                            # same as wd_heartbeat_port.
                                            # (change requires restart)
heartbeat_device0 = ''
                                            # Name of NIC device (such like 'eth0')
                                            # used for sending/receiving heartbeat
                                            # signal to/from destination 0.
                                            # This works only when this is not empty
                                            # and pgpool has root privilege.
                                            # (change requires restart)

heartbeat_destination1 = 'server3'
heartbeat_destination_port1 = 9694
heartbeat_device1 = ''

server2

heartbeat_destination0 = 'server1'
                                            # Host name or IP address of destination 0
                                            # for sending heartbeat signal.
                                            # (change requires restart)
heartbeat_destination_port0 = 9694
                                            # Port number of destination 0 for sending
                                            # heartbeat signal. Usually this is the
                                            # same as wd_heartbeat_port.
                                            # (change requires restart)
heartbeat_device0 = ''
                                            # Name of NIC device (such like 'eth0')
                                            # used for sending/receiving heartbeat
                                            # signal to/from destination 0.
                                            # This works only when this is not empty
                                            # and pgpool has root privilege.
                                            # (change requires restart)

heartbeat_destination1 = 'server3'
heartbeat_destination_port1 = 9694
heartbeat_device1 = ''

server3

heartbeat_destination0 = 'server1'
                                            # Host name or IP address of destination 0
                                            # for sending heartbeat signal.
                                            # (change requires restart)
heartbeat_destination_port0 = 9694
                                            # Port number of destination 0 for sending
                                            # heartbeat signal. Usually this is the
                                            # same as wd_heartbeat_port.
                                            # (change requires restart)
heartbeat_device0 = ''
                                            # Name of NIC device (such like 'eth0')
                                            # used for sending/receiving heartbeat
                                            # signal to/from destination 0.
                                            # This works only when this is not empty
                                            # and pgpool has root privilege.
                                            # (change requires restart)

heartbeat_destination1 = 'server2'
heartbeat_destination_port1 = 9694
heartbeat_device1 = ''

8.3.5.6. Logging

In the example, we output Pgpool-II's log to syslog.

log_destination = 'syslog'
                                    # Where to log
                                    # Valid values are combinations of stderr,
                                    # and syslog. Default to stderr.

syslog_facility = 'LOCAL1'
                                    # Syslog local facility. Default to LOCAL0

Create Pgpool-II log file.

[all servers]# mkdir /var/log/pgpool-II
[all servers]# touch /var/log/pgpool-II/pgpool.log

Edit config file of syslog /etc/rsyslog.conf.

[all servers]# vi /etc/rsyslog.conf
...
*.info;mail.none;authpriv.none;cron.none;LOCAL1.none    /var/log/messages
LOCAL1.*                                                /var/log/pgpool-II/pgpool.log

Setting logrotate same as /var/log/messages.

[all servers]# vi /etc/logrotate.d/syslog
...
/var/log/messages
/var/log/pgpool-II/pgpool.log
/var/log/secure

Restart rsyslog service.

[all servers]# systemctl restart rsyslog

The settings of Pgpool-II is completed.

8.3.6. Starting/Stopping Pgpool-II

Next we start Pgpool-II. Before starting Pgpool-II, please start PostgreSQL servers first. Also, when stopping PostgreSQL, it is necessary to stop Pgpool-II first.

Starting Pgpool-II
In section Before Starting, we already set the auto-start of Pgpool-II. To start Pgpool-II, restart the whole system or execute the following command.
```
# systemctl start pgpool.service
    
```
Stopping Pgpool-II
```
# systemctl stop pgpool.service
    
```

8.3.7. How to use

Let's start to use Pgpool-II. First, we start the primary PostgreSQL.

[server1]# su - postgres
[server1]$ /usr/pgsql-11/bin/pg_ctl start -D $PGDATA

Then let's start Pgpool-II on server1, server2, server3 by using the following command.

# systemctl start pgpool.service

8.3.7.1. Set up PostgreSQL standby server

First, we should set up PostgreSQL standby server by using Pgpool-II online recovery functionality. Ensure that recovery_1st_stage and pgpool_remote_start scripts used by pcp_recovery_node command are in database cluster directory of PostgreSQL primary server (server1).

# pcp_recovery_node -h 192.168.137.150 -p 9898 -U pgpool -n 1
Password: 
pcp_recovery_node -- Command Successful

# pcp_recovery_node -h 192.168.137.150 -p 9898 -U pgpool -n 2
Password: 
pcp_recovery_node -- Command Successful

After executing pcp_recovery_node command, verify that server2 and server3 are started as PostgreSQL standby server.

# psql -h 192.168.137.150 -p 9999 -U pgpool postgres -c "show pool_nodes"
Password for user pgpool
node_id | hostname | port | status | lb_weight |  role   | select_cnt | load_balance_node | replication_delay | replication_state | replication_sync_state | last_status_change  
---------+----------+------+--------+-----------+---------+------------+-------------------+-------------------+-------------------+------------------------+---------------------
0       | server1  | 5432 | up     | 0.333333  | primary | 0          | false             | 0                 |                   |                        | 2019-08-06 11:13:17
1       | server2  | 5432 | up     | 0.333333  | standby | 0          | true              | 0                 | streaming         | async                  | 2019-08-06 11:13:25
2       | server3  | 5432 | up     | 0.333333  | standby | 0          | false             | 0                 | streaming         | async                  | 2019-08-06 11:14:20
(3 rows)

8.3.7.2. Switching active/standby watchdog

Confirm the watchdog status by using pcp_watchdog_info. The Pgpool-II server which is started first run as MASTER.

# pcp_watchdog_info -h 192.168.137.150 -p 9898 -U pgpool
Password:
3 YES server1:9999 Linux server1 server1

server1:9999 Linux server1 server1 9999 9000 4 MASTER  #The Pgpool-II server started first becames "MASTER".
server2:9999 Linux server2 server2 9999 9000 7 STANDBY #run as standby
server3:9999 Linux server3 server3 9999 9000 7 STANDBY #run as standby

Stop active server server1, then server2 or server3 will be promoted to active server. To stop server1, we can stop Pgpool-II service or shutdown the whole system. Here, we stop Pgpool-II service.

[server1]# systemctl stop pgpool.service

# pcp_watchdog_info -p 9898 -h 192.168.137.150 -U pgpool
Password:
3 YES server2:9999 Linux server2 server2

server2:9999 Linux server2 server2 9999 9000 4 MASTER     #server2 is promoted to MASTER
server1:9999 Linux server1 server1 9999 9000 10 SHUTDOWN  #server1 is stopped
server3:9999 Linux server3 server3 9999 9000 7 STANDBY    #server3 runs as STANDBY

Start Pgpool-II (server1) which we have stopped again, and verify that server1 runs as a standby.

[server1]# systemctl start pgpool.service

[server1]# pcp_watchdog_info -p 9898 -h 192.168.137.150 -U pgpool
Password:
3 YES server2:9999 Linux server2 server2

server2:9999 Linux server2 server2 9999 9000 4 MASTER
server1:9999 Linux server1 server1 9999 9000 7 STANDBY
server3:9999 Linux server3 server3 9999 9000 7 STANDBY

8.3.7.3. Failover

First, use psql to connect to PostgreSQL via virtual IP, and verify the backend information.

# psql -h 192.168.137.150 -p 9999 -U pgpool postgres -c "show pool_nodes"
Password for user pgpool:
node_id | hostname | port | status | lb_weight |  role   | select_cnt | load_balance_node | replication_delay | replication_state | replication_sync_state | last_status_change  
---------+----------+------+--------+-----------+---------+------------+-------------------+-------------------+-------------------+------------------------+---------------------
0       | server1  | 5432 | up     | 0.333333  | primary | 0          | false             | 0                 |                   |                        | 2019-08-06 11:13:17
1       | server2  | 5432 | up     | 0.333333  | standby | 0          | true              | 0                 | streaming         | async                  | 2019-08-06 11:13:25
2       | server3  | 5432 | up     | 0.333333  | standby | 0          | false             | 0                 | streaming         | async                  | 2019-08-06 11:14:20
(3 rows)

Next, stop primary PostgreSQL server server1, and verify automatic failover.

    [server1]$ pg_ctl -D /var/lib/pgsql/11/data -m immediate stop

After stopping PostgreSQL on server1, failover occurs and PostgreSQL on server2 becomes new primary DB.

# psql -h 192.168.137.150 -p 9999 -U pgpool postgres -c "show pool_nodes"
Password for user pgpool:
node_id | hostname | port | status | lb_weight |  role   | select_cnt | load_balance_node | replication_delay | replication_state | replication_sync_state | last_status_change  
---------+----------+------+--------+-----------+---------+------------+-------------------+-------------------+-------------------+------------------------+---------------------
0       | server1  | 5432 | down   | 0.333333  | standby | 0          | false             | 0                 |                   |                        | 2019-08-06 11:36:03
1       | server2  | 5432 | up     | 0.333333  | primary | 0          | true              | 0                 |                   |                        | 2019-08-06 11:36:03
2       | server3  | 5432 | up     | 0.333333  | standby | 0          | false             | 0                 | streaming         | async                  | 2019-08-06 11:36:15
(3 rows)

server3 is running as standby of new primary server2.

[server3]# psql -h server3 -p 5432 -U pgpool postgres -c "select pg_is_in_recovery()"
pg_is_in_recovery 
-------------------
t

[server2]# psql -h server2 -p 5432 -U pgpool postgres -c "select pg_is_in_recovery()"
pg_is_in_recovery 
-------------------
f

[server2]# psql -h server2 -p 5432 -U pgpool postgres -c "select * from pg_stat_replication" -x
-[ RECORD 1 ]----+------------------------------
pid              | 11059
usesysid         | 16392
usename          | repl
application_name | server3
client_addr      | 192.168.137.103
client_hostname  | 
client_port      | 48694
backend_start    | 2019-08-06 11:36:07.479161+09
backend_xmin     | 
state            | streaming
sent_lsn         | 0/75000148
write_lsn        | 0/75000148
flush_lsn        | 0/75000148
replay_lsn       | 0/75000148
write_lag        | 
flush_lag        | 
replay_lag       | 
sync_priority    | 0
sync_state       | async
reply_time       | 2019-08-06 11:42:59.823961+09

8.3.7.4. Online Recovery

Here, we use Pgpool-II online recovery functionality to restore server1 (old primary server) as a standby. Before restoring the old primary server, please ensure that recovery_1st_stage and pgpool_remote_start scripts exist in database cluster directory of current primary server server2.

# pcp_recovery_node -h 192.168.137.150 -p 9898 -U pgpool -n 0
Password: 
pcp_recovery_node -- Command Successful

Then verify that server1 is started as a standby.

# psql -h 192.168.137.150 -p 9999 -U pgpool postgres -c "show pool_nodes"
Password for user pgpool:
node_id | hostname | port | status | lb_weight |  role   | select_cnt | load_balance_node | replication_delay | replication_state | replication_sync_state | last_status_change  
---------+----------+------+--------+-----------+---------+------------+-------------------+-------------------+-------------------+------------------------+---------------------
0       | server1  | 5432 | up     | 0.333333  | standby | 0          | false             | 0                 | streaming         | async                  | 2019-08-06 11:48:05
1       | server2  | 5432 | up     | 0.333333  | primary | 0          | false             | 0                 |                   |                        | 2019-08-06 11:36:03
2       | server3  | 5432 | up     | 0.333333  | standby | 0          | true              | 0                 | streaming         | async                  | 2019-08-06 11:36:15
(3 rows)

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