Add switch to choose listkeys or fold_objects in storage calclation

[kuenishi]

Rebased version of and supersedes #1051 (RCS-34).

[shino]

This setting item is already deprecated one. Should we care about it?

[kuenishi]

The deprecation plan is to mention in 2.0 release notes and remove the code later, like late 2.0.x or 2.1. That's why I still hold this config.

[kuenishi]

Actually, this was to ensure Riak is later than 1.4 - having 2i <<"key">> index and return_value=true in vnode folding. CS can know this thanks to riak_pb_csbucket.

[shino]

OK, understood.

[shino]

Will the new configuration item go into cuttlefish schema?

[kuenishi]

The reason why I still keep default value of use_2i_for_storage_calc as false is just I don't want to change many things at once. But I'd like to change default as true until all Riak <= 2.0.5 updated later version, at least. Maybe timing is good at 1.4 deprecation.

[kuenishi]

I don't think we have to introduce this configuration in riak-cs.conf.
With the same reason I want to keep this parameter rather well-unknown. If we change default value, then do really operators have to know it? This is minor optimisation, so we'd better omit the responsibility to explain (or even announce loud) what the configuration exactly is. Just enough and worth for advanced operators.

[kuenishi]

• Added very stupid riak_test
• Get rid of unnecessary configuration (fold_objects_for_list_keys)
• Bigger upper bound of 2i input

Ready for review again.

[shino]

The reason why I still keep default value of use_2i_for_storage_calc as false is just I don't want to change many things at once.

Understood. I won't test use_2i_for_storage_calc=true with Riak 2.0.5- .

[shino]

Not disk intensive, but did micro benchmark on my laptop, with riak_ee 2.0 branch and got similar results as you had.

About 830 K keys

> application:set_env(riak_cs, use_2i_for_storage_calc, true).

13:07:46.817 [info] Finished storage calculation in 43 seconds.
13:09:20.953 [info] Finished storage calculation in 42 seconds.
13:10:22.254 [info] Finished storage calculation in 42 seconds.

> application:set_env(riak_cs, use_2i_for_storage_calc, false).

13:12:45.069 [info] Finished storage calculation in 81 seconds.
13:14:04.226 [info] Finished storage calculation in 75 seconds.
13:15:24.673 [info] Finished storage calculation in 78 seconds.

> application:set_env(riak_cs, use_2i_for_storage_calc, true). %% sanity check

13:16:23.934 [info] Finished storage calculation in 41 seconds.

[shino]

riak_test passed with riak_ee 2.0 branch.

[shino]

@borshop merge

[shino]

Memo: The change basho/riak_kv#1072 is included in Riak 2.0.6 and 2.1.0+.