Streaming replication problem: Master makes committed change which standby follows but master gets locked

Problem

Streaming replication works somewhat in the sense that a transaction in master gets locked after commit but the changes can be seen in standby.

Cause

Master cannot associate success of replication with standby. I do not now why this is needed anyway, why it is not sufficient to know that there are as many success stories.

Solution

resolve.config (standby) contains the variable primary_conninfo which needs to contain the parameter application_name. Its associated value must show up in the list of masters postgres.config synchronous_standby_names.

primary_conninfo = 'application_name=main2 ...'
synchronous_standby_names = main2,main3,main4