Postgresql BDR(Bi-Directional Replication) Latency Monitoring

Hi All,

I'm looking at BDR monitoring documentation at this location
https://wiki.postgresql.org/wiki/BDR_Monitoring

I understand the query in documentation:

select slot_name, plugin, database, active, xmin,
pg_get_transaction_committime(xmin)
FROM pg_stat_logical_decoding ;

Should be:

select slot_name, plugin, database, active, xmin,
pg_get_transaction_committime(xmin)
FROM pg_replication_slots ;

I am running PostgreSQL 9.4.0 bits on Centos:

postgresql-bdr94-contrib-9.4.0_bdr1-1_2ndQuadrant.el6.x86_64
postgresql-bdr94-libs-9.4.0_bdr1-1_2ndQuadrant.el6.x86_64
postgresql-bdr94-bdr-0.8.0beta1-1_2ndQuadrant.el6.x86_64
postgresql-bdr94-2ndquadrant-redhat-1.0-2.noarch
postgresql-bdr94-devel-9.4.0_bdr1-1_2ndQuadrant.el6.x86_64
postgresql-bdr94-server-9.4.0_bdr1-1_2ndQuadrant.el6.x86_64
postgresql-bdr94-9.4.0_bdr1-1_2ndQuadrant.el6.x86_64

We have 3 nodes set-up. We would like to understand the latency between
nodes.

When using http://oltpbenchmark.com/ to create a load on one node, I would
expect the 'xmin' value not to be null but is.

What is the best way to monitor replication latency when using Postgresql
BDR?

Regards,

Bill