Re: [External] JDBC Postgres Failover with quorum based synchronous replication

I guess the distinction between master and secondary logic can be looked up here(isMaster)
https://github.com/pgjdbc/pgjdbc/blob/f78a639d1ed3c64e80e1fa107691b4af5945cb84/pgjdbc/src/main/java/org/postgresql/core/v3/ConnectionFactoryImpl.java
and from within slaves iirc we did check the code and it is random shuffle and does not support any custom logic to pick any slaves.
I might be wrong but I do remember looking it up in the source :)

Regards,
Vijay

________________________________________
From: Debraj Manna <subharaj.manna@gmail.com>
Sent: Sunday, June 17, 2018 11:31:32 AM
To: pgsql-admin
Subject: [External] JDBC Postgres Failover with quorum based synchronous replication

Hi

Let's say I am using quorum based synchronous replication<https://wiki.postgresql.org/wiki/New_in_postgres_10#Quorum_Commit_for_Synchronous_Replication> either ANY or FIRST in synchronous_standby_names

I am trying to read from slave as discussed here<https://jdbc.postgresql.org/documentation/head/connect.html>.

jdbc:postgresql://node1,node2,node3/accounting?targetServerType=preferSlave&loadBalanceHosts=true

Can someone let me know

  1.  How does a slave is selected? Is a slave randomly selected or a slave is preferred which has zero lag or the minimum lag?
  2.  Is there any setting in jdbc url which will only select the slave with zero replication and if no such slave exists then read will be sent to master ?

Thanks,