HOW TO SETUP/CONFIGURE THE POSTGRESQL STREAMING REPLICATION ON POSTGRESQL 10?

what is the postgresql Streaming Replication (SR) ?
Streaming Replication (SR) provides the capability to continuously ship and apply the WAL XLOG records to some number of standby servers in order to keep them current. This feature was added to PostgreSQL 9.0. 

Advantages of postgresql Streaming Replication (SR):
1.Switch over/Fail over after the primary fails.
2.Data loss so less and data integrity.
3.No need more down time after primary fail.
4.synchronous mode Zero data loss.
5. Load balancing using load balancer ex.pgpool-II,pgbouncer.
6.Auto failover using repmgr.

Now We can go postgresql streaming replication setup using postgresql-10.3 versionmaster IP: 192.168.2.2  slave IP: 192.168.2.3

NetWork Configuration :

On Master:

[postgres@master ]$ cat /etc/redhat-release Red Hat Enterprise Linux Server release 7.3 Beta (Maipo)--Netcard Entrycd /etc/sysconfig/network-scripts/vi ifcfg-ens33BOOTPROTO=staticIPADDR=192.168.2.2NETMASK=255.255.255.0DEVICE="ens33"ONBOOT=yesvi /etc/sysconfig/networkNETWORKING=yesHOSTNAME=masterGATEWAY=192.168.2.1## Configure DNS Server# vi /etc/resolv.confnameserver 8.8.8.8 # Replace with your nameserver ipnameserver 192.168.2.1  # Replace with your nameserver ip--Host Entryvi /etc/hosts192.168.2.2 master --Restart the network services#systemctl restart network(OR)#service network restart

FOR SLAVE SERVER:

--Netcard Entrycd /etc/sysconfig/network-scripts/vi ifcfg-ens33BOOTPROTO=staticIPADDR=192.168.2.3NETMASK=255.255.255.0DEVICE="ens33"ONBOOT=yesvi /etc/sysconfig/networkNETWORKING=yesHOSTNAME=slaveGATEWAY=192.168.2.1## Configure DNS Server# vi /etc/resolv.confnameserver 8.8.8.8 # Replace with your nameserver ipnameserver 192.168.2.1  # Replace with your nameserver ip--Host Entryvi /etc/hosts192.168.2.3 slave --Restart the network services#systemctl restart network(Or)#service network restart

On Server 192.168.2.2:-

ping 192.168.2.2ping 192.168.2.3If not ping use Telnet :telnet 192.168.2.2 5432telnet 192.168.2.3 5432

On Server 192.168.2.3:-

ping 192.168.2.2ping 192.168.2.3If not ping use Telnet :telnet 192.168.2.2 5432telnet 192.168.2.3 5432

Note : 5432 is database port for EDB 5444 you can give what you given at the time of postgres installation, if not reaching the destination host issue with Firewall you have add firewall rule else open the Database port  of 5444 or 5432

ON SLAVE:
stop the slave server

/usr/pgsql-10/bin/pg_ctl -D /var/lib/pgsql/10/data/ stop 

--move the data directory to backup location:mv /var/lib/pgsql/10/data/* /home/postgres/backup/

ON MASTER:on postgresql.conf:

listen_addresses = 'localhost,192.168.2.2'  wal_level = replica # minimal, replica, or logicalarchive_mode = on archive_command =  'rsync -av %p /home/postgres/archive/%f && rsync -av %p postgres@192.168.2.3:/home/postgres/archive/%f'max_wal_senders = 2 wal_keep_segments = 10

on pg_hba.conf:

hostreplication postgres192.168.2.3/24  md5

Restart the master server:

/usr/pgsql-10/bin/pg_ctl -D /var/lib/pgsql/10/data/ restart

taking consistancy backup:

$ psql -c "select pg_start_backup('initial_backup');"$ rsync -cva --inplace /var/lib/pgsql/10/data/* postgres@192.168.2.3:/var/lib/pgsql/10/data/$ psql -c "select pg_stop_backup();"

ON SLAVE:
on postgresql.conf:

listen_addresses = 'localhost,192.168.2.2'  wal_level = replica # minimal, replica, or logicalarchive_mode = on archive_command = '/bin/cp -av %p /home/postgres/archive/%f'max_wal_senders = 2 wal_keep_segments = 10hot_standby = on

on pg_hba.conf:

hostreplication postgres192.168.2.2/24  md5

On recovery.conf

cat /var/lib/pgsql/10/data/recovery.confstandby_mode = 'on'  # to enable the standby (read-only) mode.primary_conninfo = 'host=192.168.2.2 port=5432 user=postgres password=postgres' # to specify a connection info to the master node.trigger_file = '/tmp/pg_failover_trigger' # to specify a trigger file to recognize a fail over.restore_command = 'cp /home/postgres/archive/%f "%p"'archive_cleanup_command = '/usr/pgsql-10/bin/pg_archivecleanup /home/postgres/archive/ %r'

Restart the slave server:

/usr/pgsql-10/bin/pg_ctl -D /var/lib/pgsql/10/data/ restart

if you get any error error like arch missing wal log ...etc while restarting slave server again take the incremental physical backup

$ psql -c "select pg_start_backup('initial_backup');"$ rsync -cva --inplace --exclude=pg_hba.conf --exclude=postgresql.conf --exclude=recovery.conf /var/lib/pgsql/10/data/* postgres@192.168.2.3:/var/lib/pgsql/10/data/$ psql -c "select pg_stop_backup();"

WHILE RESTARTING SLAVE SERVER GOT FOLLOWING ERROR:

[postgres@slave root]$ /usr/pgsql-10/bin/pg_ctl -D /var/lib/pgsql/10/data/ restartcould not change directory to "/root": Permission deniedpg_ctl: PID file "/var/lib/pgsql/10/data/postmaster.pid" does not existIs server running?starting server anywaywaiting for server to start....2018-05-26 20:36:34.834 IST [45453] LOG:  listening on IPv6 address "::1", port 54322018-05-26 20:36:34.834 IST [45453] LOG:  listening on IPv4 address "127.0.0.1", port 54322018-05-26 20:36:34.836 IST [45453] LOG:  listening on IPv4 address "192.168.2.3", port 54322018-05-26 20:36:34.840 IST [45453] LOG:  listening on Unix socket "/var/run/postgresql/.s.PGSQL.5432"2018-05-26 20:36:34.849 IST [45453] LOG:  listening on Unix socket "/tmp/.s.PGSQL.5432".2018-05-26 20:36:35.685 IST [45453] LOG:  redirecting log output to logging collector process2018-05-26 20:36:35.685 IST [45453] HINT:  Future log output will appear in directory "log".

ON LOG FILE:

tail -f postgresql-2018-05-26_203635.log2018-05-26 20:36:35.957 IST [45461] FATAL:  could not connect to the primary server: FATAL:  password authentication failed for user "postgres"cp: cannot stat ‘/home/postgres/archive/000000010000000000000006’: No such file or directory2018-05-26 20:36:40.964 IST [45465] FATAL:  could not connect to the primary server: FATAL:  password authentication failed for user "postgres"cp: cannot stat ‘/home/postgres/archive/000000010000000000000006’: No such file or directory2018-05-26 20:36:45.963 IST [45467] FATAL:  could not connect to the primary server: FATAL:  password authentication failed for user "postgres"cp: cannot stat ‘/home/postgres/archive/000000010000000000000006’: No such file or directory2018-05-26 20:36:50.977 IST [45471] FATAL:  could not connect to the primary server: FATAL:  password authentication failed for user "postgres"2018-05-26 20:36:55.459 IST [45453] LOG:  received fast shutdown request2018-05-26 20:36:55.465 IST [45457] LOG:  shutting down2018-05-26 20:36:55.472 IST [45453] LOG:  database system is shut down

on master:
--change the postgres password becouse you given wrong password on recovery.conf file for postgres user so change the password as per recovery.conf

alter user postgres with password 'postgres';

Then Restart the slave server:

 /usr/pgsql-10/bin/pg_ctl -D /var/lib/pgsql/10/data/ restart

MONITORING STREAMING REPLICATION:
At MASTER:
1.create some dummy table check the slave server whther is replicated or not.

postgres=# create table t(id int);CREATE TABLE

--check master server whether is recovery mode or not, 

master will not be recovery mode slave only will be recovery mode.

 postgres=# select pg_is_in_recovery(); pg_is_in_recovery ------------------- f(1 row)2.Using pg_stat_replication viewspostgres=# select client_addr,client_hostname,client_port,state,sent_lsn,write_lsn,flush_lsn,replay_lsn,write_lag,replay_lag,flush_lag,sync_state from pg_stat_replication; client_addr | client_hostname | client_port | state | sent_lsn  | write_lsn | flush_lsn | replay_lsn | write_lag | replay_lag | flush_lag | sync_state-------------+-----------------+-------------+-----------+-----------+-----------+-----------+------------+-----------+------------+-----------+------------ 192.168.2.3 | | 60000 | streaming | 0/8017A28 | 0/8017A28 | 0/8017A28 | 0/8017A28  | || | async(1 row)

3.using linux command check the wal sender process whether started or not:

[postgres@mster ]$ ps -ef|grep postgresroot  82472  82437  0 08:34 pts/100:00:00 su postgrespostgres  82473  82472  0 08:34 pts/100:00:00 bashroot  94549  94494  0 20:36 pts/300:00:00 su postgrespostgres  94550  94549  0 20:36 pts/300:00:00 bashpostgres  94582  1  0 20:36 pts/300:00:00 /usr/pgsql-10/bin/postgres -D /var/lib/pgsql/10/datapostgres  94584  94582  0 20:36 ?00:00:00 postgres: logger processpostgres  94586  94582  0 20:36 ?00:00:00 postgres: checkpointer processpostgres  94587  94582  0 20:36 ?00:00:00 postgres: writer processpostgres  94588  94582  0 20:36 ?00:00:00 postgres: wal writer processpostgres  94589  94582  0 20:36 ?00:00:00 postgres: autovacuum launcher processpostgres  94591  94582  0 20:36 ?00:00:00 postgres: stats collector processpostgres  94592  94582  0 20:36 ?00:00:00 postgres: bgworker: logical replication launcherpostgres  94741  94582  0 20:43 ?00:00:00 postgres: wal sender process postgres 192.168.2.3(60000) streaming 0/8017B08postgres  95178  94550  0 21:08 pts/300:00:00 ps -efpostgres  95179  94550  0 21:08 pts/300:00:00 grep --color=auto postgres

--you can calculate using this linux command how many wal sender is replicated to slave.

$ ps -ef|grep senderpostgres 7585 3383  0 15:59 ?00:00:00 postgres: wal sender process postgres 192.168.2.2(42586) streaming 0/18017CD8postgres 7598 6564  0 15:59 pts/200:00:00 grep --color=auto sender

AT SLAVE SERVER:
1.check the previously created table whether is replicated or not

postgres=# \dt List of relations Schema | Name  | Type  |  Owner--------+---------------+-------+---------- public | qrtransaction | table | postgres public | t | table | postgres(2 rows)

yes! it is successfully replicated the table.
--check the slave mode using following function whether is recovery mode or not

postgres=# select pg_is_in_recovery(); pg_is_in_recovery ------------------- t(1 row)

--and try to insert the valuse on slave server, slave is a read only mode it will not permitted write transaction.

postgres=# insert into t values(1);ERROR:  cannot execute INSERT in a read-only transaction

2. using pg_stat_replication view:

postgres=# select status,receive_start_lsn,received_lsn,last_msg_send_time,latest_end_lsn,latest_end_time,conninfo from pg_stat_wal_receiver ;  status | receive_start_lsn | received_lsn |last_msg_send_time| latest_end_lsn | latest_end_time  | conninfo-----------+-------------------+--------------+----------------------------------+----------------+----------------------------------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- streaming | 0/6000000 | 0/8017B08| 2018-05-26 21:26:34.577733+05:30 | 0/8017B08  | 2018-05-26 21:06:32.309548+05:30 | user=postgres password=******** dbname=replication host=192.168.2.2 port=5432 fallback_application_name=walreceiver sslmode=prefer sslcompression=1 krbsrvname=postgres target_session_attrs=any(1 row)

3.using linux command you can monitor wether wal receiver is started or not.this linux command will be helpful for finding out the postgres data directory as well as postgres utility path means bin path

[postgres@slave data]$ ps -ef|grep postgresroot 3971 3573  0 10:27 pts/000:00:00 su postgrespostgres 3972 3971  0 10:27 pts/000:00:00 bashroot  45410  45321  0 20:36 pts/100:00:00 su postgrespostgres  45411  45410  0 20:36 pts/100:00:00 bashpostgres  45606  1  0 20:43 pts/100:00:00 /usr/pgsql-10/bin/postgres -D /var/lib/pgsql/10/datapostgres  45607  45606  0 20:43 ?00:00:00 postgres: logger processpostgres  45608  45606  0 20:43 ?00:00:00 postgres: startup process recovering 000000010000000000000008postgres  45610  45606  0 20:43 ?00:00:00 postgres: checkpointer processpostgres  45611  45606  0 20:43 ?00:00:00 postgres: writer processpostgres  45612  45606  0 20:43 ?00:00:06 postgres: wal receiver process streaming 0/8017B08postgres  45613  45606  0 20:43 ?00:00:00 postgres: stats collector processpostgres  45995  45411  0 21:16 pts/100:00:00 ps -efpostgres  45996  45411  0 21:16 pts/100:00:00 grep --color=auto postgres

4.this command will be helpful for how many wal segment get postgres receiver 

[postgres@slave data]$ ps -ef|grep receiver;postgres  45612  45606  0 20:43 ?00:00:06 postgres: wal receiver process streaming 0/8017B08postgres  46018  45411  0 21:18 pts/100:00:00 grep --color=auto receiver

5.If the slave is up in hot standby mode, you can tell the time in seconds the delay of transactions applied on the slave with this query:

postgres=# select now() - pg_last_xact_replay_timestamp() AS replication_delay; replication_delay------------------- 00:18:35.207663(1 row)

Note: above timing is noted for last 18 minutes slave not get any transaction

Know More About Replication:  https://www.agussyarif.com/search/label/Replication

cascaded replication setup/configuration : https://www.agussyarif.com/2018/03/how-to-configure-cascade-replication-on.html