Re: postgres streaming replication for HA

Hi Samed,

This is the output of ps –ef | grep post, on slave node , after I followed the steps given in my last email.

00:00:00 -bash
00:00:00 /usr/pgsql-9.6/bin/postmaster -D /var/lib/pgsql/9.6/data/
00:00:00 postgres: logger process
00:00:00 postgres: startup process recovering 000000040000000000000014
00:00:00 postgres: checkpointer process
00:00:00 postgres: writer process
00:00:00 postgres: stats collector process
00:00:01 postgres: wal receiver process streaming 0/140030E8
00:00:00 ps -ef
00:00:00 grep --color=auto post

Thanks,
Sunil

From: Sunil N Shinde
Sent: 08 September 2017 16:41
To: 'Samed YILDIRIM' <samed(at)reddoc(dot)net>; pgsql-admin(at)postgresql(dot)org
Subject: RE: [ADMIN] postgres streaming replication for HA

Hi Samed,

Thanks a lot. Will try this.

Please find below the contents of recovery.conf file.

standby_mode = 'on'
primary_conninfo = 'host=*.*.*.* port=5432 user=replica password=***** application_name=****'
restore_command = 'cp /var/lib/pgsql/9.6/data/archive/%f %p'
trigger_file = '/tmp/postgresql.trigger.5432'
recovery_target_timeline = 'latest'

I have tried below steps. Can you please tell me whether this is right way?

1. Brought down master node.

2. Copied missing archive logs from master to slave.

3. On slave --- touch /tmp/postgresql.trigger.5432 --- Hence it has became NEW MASTER.

4. On old master --- rm /tmp/postgresql.trigger.5432 & addred recovery.conf file with old slave’s connectinfo --- Hence it has become NEW SLAVE.

Thanks & Regards,
Sunil N Shinde
Assistant Manager – DBA
Mastek Ltd | Mastek Millennium Center, Millennium Business Park, Mahape, Navi Mumbai-400710 .
Mob:- 9819002393

From: Samed YILDIRIM [mailto:samed(at)reddoc(dot)net]
Sent: 08 September 2017 16:25
To: Sunil N Shinde <Sunil(dot)Shinde(at)mastek(dot)com<mailto:Sunil(dot)Shinde(at)mastek(dot)com>>; pgsql-admin(at)postgresql(dot)org<mailto:pgsql-admin(at)postgresql(dot)org>
Subject: Re: [ADMIN] postgres streaming replication for HA

Hi Shinde,

Could you please share recovery.conf file?

Logs means that xlog file (000000030000000000000013) which is required by your standby has been removed before streamed to standby. To avoid this kind of situations you can use replication slot or you should set wal_keep_segment high enough.

Best regards.
Samed YILDIRIM

08.09.2017, 11:40, "Sunil N Shinde" <sunil(dot)shinde(at)mastek(dot)com<mailto:sunil(dot)shinde(at)mastek(dot)com>>:

Hi Samed,

Please find below the log details also :

cp: cannot stat ‘/var/lib/pgsql/9.6/data/archive/000000030000000000000013’: No such file or directory

< 2017-09-08 08:36:25.852 UTC > LOG: started streaming WAL from primary at 0/13000000 on timeline 3

< 2017-09-08 08:36:25.852 UTC > FATAL: could not receive data from WAL stream: ERROR: requested starting point 0/13000000 is ahead of the WAL flush position of this server 0/1102FFF0

Thanks & Regards,
Sunil N Shinde
Assistant Manager – DBA
Mastek Ltd | Mastek Millennium Center, Millennium Business Park, Mahape, Navi Mumbai-400710 .
Mob:- 9819002393

From: pgsql-admin-owner(at)postgresql(dot)org<mailto:pgsql-admin-owner(at)postgresql(dot)org> [mailto:pgsql-admin-owner(at)postgresql(dot)org<mailto:pgsql-admin-owner(at)postgresql(dot)org>] On Behalf Of Sunil N Shinde
Sent: 08 September 2017 12:38
To: Samed YILDIRIM <samed(at)reddoc(dot)net<mailto:samed(at)reddoc(dot)net>>; pgsql-admin(at)postgresql(dot)org<mailto:pgsql-admin(at)postgresql(dot)org>
Subject: Re: [ADMIN] postgres streaming replication for HA

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Hi Samed,

Thanks for the quick reply.

I am trying it manually with below step:

1. Shut down the primary node

2. Creating trigger file on standby node before promoting it to primay.

3. "recovery_target_timline='latest'” adding this parameter in recovery file on standby and restarting it.

On current standby :

psql -p 5432 -c "select pg_is_in_recovery();"

pg_is_in_recovery

-------------------

t

(1 row)

But on Current Primary:

psql -c "select application_name, state, sync_priority, sync_state from pg_stat_replication;"

application_name | state | sync_priority | sync_state

------------------+-------+---------------+------------

(0 rows)

Thanks & Regards,
Sunil N Shinde

From: Samed YILDIRIM [mailto:samed(at)reddoc(dot)net]
Sent: 08 September 2017 12:22
To: pgsql-admin(at)postgresql(dot)org<mailto:pgsql-admin(at)postgresql(dot)org>; Sunil N Shinde <Sunil(dot)Shinde(at)mastek(dot)com<mailto:Sunil(dot)Shinde(at)mastek(dot)com>>
Subject: Re: [ADMIN] postgres streaming replication for HA

Hi Shinde,

Do you trying swithover manually? Or do you use any manager or script to handle switchover operation?

Best regards.

--
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08:51, 8 Eylül 2017, Sunil N Shinde <sunil(dot)shinde(at)mastek(dot)com<mailto:sunil(dot)shinde(at)mastek(dot)com>>:

Hi,

I am forming 2 node cluster of streaming replication for HA. I could able to succeed with the replication process.

But I am not able to complete the “switchover”.

Version : postgresql-9.6

OS :RHEL7

Master Node Parameters:

wal_level = hot_standby

synchronous_commit = local

archive_mode = on

archive_command = 'cp %p /var/lib/pgsql/9.6/data/archive/%f'

max_wal_senders = 2

wal_keep_segments = 10

synchronous_standby_names = 'UWPGRECLUS2'

pb_hba.conf

# Localhost

host replication replica 127.0.0.1/32 md5

# PostgreSQL Master IP address

host replication replica 10.0.3.4/32 md5

# PostgreSQL SLave IP address

host replication replica 10.0.3.5/32 md5

Slave Node Parameters:

wal_level = hot_standby

synchronous_commit = local

max_wal_senders = 2

wal_keep_segments = 10

synchronous_standby_names = 'UWPGRECLUS2'

hot_standby = on

Replication is properly happening from master to slave. But I am not able to switchover between the nodes.

Can anyone please guide me in this regard?

Thanks & Regards,

Sunil N Shinde

Assistant Manager – DBA

Mastek Ltd | Mastek Millennium Center, Millennium Business Park, Mahape, Navi Mumbai-400710 .

Mob:- 9819002393