fix forward iterator bug

Summary: obvious

Test Plan: db_test

Reviewers: sdong, haobo, igor

Reviewed By: igor

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D18987
collect metrics for in memory workload get/seek

Summary:
collect in-memory workload get/seek metrics so that we can alert on
regression

Test Plan: ran locally

Reviewers: igor

Reviewed By: igor

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D18969
BlockBasedTable::PrefixMayMatch() to bloom setting to the beginning of the function

Summary: In BlockBasedTable::PrefixMayMatch() we calculate prefix even if bloom is not config. Move the check before

Test Plan: make all check

Reviewers: igor, ljin

Reviewed By: ljin

Subscribers: wuj, leveldb, haobo, yhchiang, dhruba

Differential Revision: https://reviews.facebook.net/D18993