tx canceled on standby despite infinite max_standby_streaming_delay

[Jay Howard <jhoward@xxxxxxxxxxxxxxxxx>]

I'm seeing long-running transactions (pg_dump) canceled on the standby when there are a lot of inserts happening on the master.  This despite my having set max_standby_streaming_delay to -1 on the standby.

Why might that happen?

This is pg 9.3.12.  When it happens I see:

pg_dump: Dumping the contents of table "TABLE" failed: PQgetResult() failed.
pg_dump: Error message from server: ERROR:  canceling statement due to conflict with recovery
DETAIL:  User query might have needed to see row versions that must be removed.
pg_dump: The command was: COPY public.TABLE (COLUMNS) TO stdout;