Under-utilised Features - Long Term Plan

[martinsumner]

There are some features within riak_core, that are rarely or never used. Should these features simply be removed going forward.

riak_core_bg_manager

• Used potentially in three places: riak_repl fullsync (riak_repl.fullsync_use_background_manager); riak_kv handoff (riak_kv.handoff_use_background_manager); riak_kv hashtree aae (riak_kv.aae_use_background_manager).
• In all three cases by default the use of background manager is configured to off.

riak_core_throttle

• Used only within riak_kv_entropy_manager.

riak_core_table_owner

• Used only by riak_core_throttle (see above).

gen_nb_server

• Used in riak_core_handoff_listener, and in riak_api in riak_api_pb_listener.
• Reason why a specific non-block server for TCP handling is required unknown.
• Was previously used in riak_repl, but since replaced by use of ranch.
• Question whether dedicated riak_core_handoff_listener is needed, with improvements to Erlang Distribution Protocol that may help with potential issues with inter-node traffic being overwhelmed with handoff data?
• An alternative may be to use approach in nextgenrepl i.e. make handoff part of the API, and use the riak erlang client for handoff as this helps with issues with maintaining SSL/TLS compatability.

process_proxy

• Used only in riak_core_handoff_listener.
• Reasons unclear as to why it is required.

bloom

• Not used anywhere. riak_repl uses ebloom.

riak_core_tracer|riak_core_dtrace

• riak_core_tracer only used in riak_kv, within riak_kv_get_fsm eunit test.
• Do real-world Riak users use this?

riak_core_gen_server

• Taken from LShift/RabbitMQ originally - adds a priority queue in-front of the standard process mailbox. The RabbitMQ code still includes gen_server2 which appears to be an updated version of this.
• Used only in riak_core_handoff_receiver and within riak_repl in riak_repl_fullsync_helper, but no use of priority.
• Related PR for vernemq

riak_core_priority_queue

• Used only within riak_core_gen_server (see above).

[martinsumner]

Also:

riak_core_exo_monitor

• Is advertised as a way of bridging between "legacy" folsom stats i.e. defined as legacy mapping module folsom metrics to exometer.
• Only referred to in riak_repl.app.src.
• There appears to be a complicating issue with riak_repl stats in that it is directly referring to folsom, and the latest release of exometer_core removes folsom (as well as bear).
• Is the migration from folsom partial, managed in riak_kv but not in riak_repl?

[Bob-The-Marauder]

I've asked internally and as far as I know, the only potential candidate we have for retention is the riak_core_bg_manager for a little relief for overstressed systems. Even then, it is rarely used.

Possibly add dtrace to the list of items for removal as well?