Re: Broken replication in 3 node setup, master halt, standby 1 promoted, standby 2 - replication not working

[Shreeyansh Dba <shreeyansh2014@xxxxxxxxx>]

Hi Pritam Barhate,

Please check after promoting pg2 as master pg3 is up and running.
Provide Ip address of pg2 in recovery.conf of pg3 instead  hostname and pass recovery_target_timeline='latest'  ​

Also check archive_command in postgresql.conf of pg2 and restore_command in recovery.conf of pg3 is identical. and permission for pgbackrest.

​​

Hope this helps..

Best Regards,

Shreeyansh

On Thu, Jan 11, 2018 at 12:36 AM, Pritam Barhate <pritambarhate@xxxxxxxxx> wrote:

Hi,

I am trying to test the failover scenario on a brand new 3 node setup. 

pg1 is master

pg2 and pg3 are standby hosts in streaming replication, both following pg1. 

When I halt pg1, promote pg2 and update recovery.conf on pg3 to point to pg2, the replication is broken. Can you please help me identify the correct procedure to achieve this failover? 

Here are the details:

Software Versions:

PostgreSQL: 9.6

Ubuntu 16.04

PgBackRest 1.25

Here is the scenario:

Set up 3 nodes in streaming replication:

master (pg1), standby 1 (pg2), standby 2 (pg3)

Also, I have set up pgbackrest, to back up from standby. It's working correctly.

Run the following on pg1:

sudo -u postgres psql -x -c "select * from pg_stat_replication;"

-[ RECORD 1 ]----+------------------------------

pid              | 20714

usesysid         | 16384

usename          | replicator

application_name | walreceiver

client_addr      | 10.0.15.11

client_hostname  | 

client_port      | 48640

backend_start    | 2018-01-10 18:17:46.105694+00

backend_xmin     | 

state            | streaming

sent_location    | 0/6000060

write_location   | 0/6000060

flush_location   | 0/6000060

replay_location  | 0/6000060

sync_priority    | 0

sync_state       | async

-[ RECORD 2 ]----+------------------------------

pid              | 20715

usesysid         | 16384

usename          | replicator

application_name | walreceiver

client_addr      | 10.0.15.12

client_hostname  | 

client_port      | 42198

backend_start    | 2018-01-10 18:17:48.712575+00

backend_xmin     | 

state            | streaming

sent_location    | 0/6000060

write_location   | 0/6000060

flush_location   | 0/6000060

replay_location  | 0/6000060

sync_priority    | 0

sync_state       | async

It reports both the standbys working correctly. 

Halt pg1. 

On pg2:

sudo -u postgres pg_ctlcluster 9.6 main promote

On pg3:

sudo service postgresql stop

sudo -u postgres vim /var/lib/postgresql/9.6/main/recovery.conf

modify it's contents are as follows:

```

primary_conninfo = 'host=pg2 port=5432 user=replicator'

standby_mode = 'on'

restore_command = '/usr/bin/pgbackrest --stanza=main archive-get %f "%p"'

```

sudo service postgresql start

On pg2:

sudo -u postgres psql -x -c "select * from pg_stat_replication;"

-[ RECORD 1 ]----+------------------------------

pid              | 21238

usesysid         | 16384

usename          | replicator

application_name | walreceiver

client_addr      | 10.0.15.12

client_hostname  | 

client_port      | 44852

backend_start    | 2018-01-10 18:22:20.980701+00

backend_xmin     | 

state            | startup

sent_location    | 

write_location   | 

flush_location   | 

replay_location  | 

sync_priority    | 0

sync_state       | async

As you can see sent_location, write_location, flush_location all are empty. 

On pg3:

tail -f /var/log/postgresql/postgresql-9.6-main.log 

2018-01-10 18:22:19.490 UTC [21229] LOG:  restored log file "000000010000000000000005" from archive

2018-01-10 18:22:19.497 UTC [21229] LOG:  redo starts at 0/5000028

2018-01-10 18:22:19.757 UTC [21243] postgres@postgres FATAL:  the database system is starting up

2018-01-10 18:22:20.188 UTC [21229] LOG:  restored log file "000000010000000000000006" from archive

2018-01-10 18:22:20.195 UTC [21229] LOG:  consistent recovery state reached at 0/7000000

2018-01-10 18:22:20.195 UTC [21228] LOG:  database system is ready to accept read only connections

2018-01-10 18:22:20.812 UTC [21229] LOG:  invalid magic number 0000 in log segment 000000010000000000000007, offset 0

2018-01-10 18:22:20.824 UTC [21255] LOG:  fetching timeline history file for timeline 2 from primary server

2018-01-10 18:22:20.828 UTC [21255] LOG:  primary server contains no more WAL on requested timeline 1

2018-01-10 18:22:21.417 UTC [21255] LOG:  primary server contains no more WAL on requested timeline 1

At this point is I insert data in pg2, it doesn't reflect in pg3. 

Please help. 

Regards,

Pritam.

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