Using the recently added IndexedSet::const_iterator
(https://github.com/apple/foundationdb/pull/3185), we can improve the
const-correctness of many functions. In this PR const is added where
applicable. Also, wherever I came across the following while adding
const, I made the following changes:
- virtual function overrides are marked as override
- NULL is replaced with nullptr
- git clang-format is applied
Added an optimization to use a separate set for throttled events. Since this set is expected to be small, comparison of every event against this set is going to be cheaper.
Trace Events are sampled and cached with an expiration set. Every TraceEvent above SevDebug is checked against this cache to see if it exceeded a set threshold. If yes, then throttle the TraceEvent.
If a TraceEvent is throttled, a warning msg is logged.