BUG #12910: Memory leak with logical decoding

The following bug has been logged on the website:

Bug reference:      12910
Logged by:          Peter Slavov
Email address:      pet.slavov@gmail.com
PostgreSQL version: 9.4.1
Operating system:   Debian wheezy
Description:

Hi,
I am trying to use logical decoding to replay the data modifying queries on
a different server, to synchronize some of the tables. The primary server
has some load, but not so much. I am getting the changes with
pg_logical_slot_get_changes limiting the changes to 50 at a time.
At some point pg_logical_slot_get_changes queries become slow and starts to
eat all the ram and swap, which eventually kills the primary database with
this error:
 FATAL:  the database system is in recovery mode.

The nature of changes on the primary can have a lot of data in one
transaction. Which I guess is the reason of the slow
pg_logical_slot_get_changes.