Pgsql resource agent of pacemaker

Need advise on below situation:

Postgres 9.6

We are testing HA setup on a two node cluster using pacemaker, corosync stack. The replication is streaming replication in async mode.

Whenever there is a failover to standby, pgsql created a PGSQL.lock file in /var/lib/pgsql/tmp/ folder. We noticed that this file is created at random on any one of the nodes. 

Want to know:

- Is there any logic behind which node it creates the lock file? 

- When a node in kept in HS:alone state ? 

- How can we check if failed node is at a log location behind current primary? So that we can force RA to start by deleting lock file? 

Please help to understand

Thanks.