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Is there any way to have more than one PostgreSQL slave servers in the same system.

If yes, how come a master detect each server as different slaves from the below query

select * from pg_stat_replication;

will give one row for each slave which are connected to it, with PID, IP-address/client_address, client_port, etc..

If two servers are running in the same machine gives the same IP-address so it is not a unique identifier.

If slave got restarted then both client_port and PID will change so these are also cant be a unique identifier.

So, what is the unique identifier used by Postgres master to identify each slave server uniquely? Or how it is finding its slave servers differently?

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The master does not "find" the replicas. The replicas find the master.

The master identifies the replicas by either their slot_name, or their application_name, or not at all, depending on the context.

What are you trying to do?

  • In that case how come master is generating pg_stat_repication view with different slaves uniquely? – manvith Apr 23 at 8:50
  • Active WAL senders are identified by their process id. This isn't much of an identifier, as it is not stable across system (or just WAL sender) restarts. – jjanes Apr 23 at 16:06

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