ETS table with only counters

Hi guys,

I've a ETS (type of "set") which contains ONLY counters
(ets:update_counter/3).

This table is heavily used and the counters get incremented and decremented
at different rates.

Question: how should i set my table?
1. both concurrency set to true:
    [ set
    , {read_concurrency, true}
    , {write_concurrency, true} ].

2. only read concurrency set to true:
    [ set
    , {read_concurrency, true}
    , {write_concurrency, false} ].

3. only write concurrency set to true:
    [ set
    , {read_concurrency, false}
    , {write_concurrency, true} ].

Please explain why?

/Frank