Summary:
Earlier way to record in histogram=>
Linear search BucketLimit array to find the bucket and increment the
counter
Current way to record in histogram=>
Store a HistMap statically which points the buckets of each value in the
range [kFirstValue, kLastValue);
In the proccess use vectors instead of array's and refactor some code to
HistogramHelper class.
Test Plan:
run db_bench with histogram=1 and see a histogram being
printed.
Reviewers: dhruba, chip, heyongqiang
Reviewed By: chip
CC: leveldb
Differential Revision: https://reviews.facebook.net/D8265
