commit b5fda565d4bad66f3b5a6432236b96743ccfd323
Author: Steaphan Greene <steaphan@fb.com>
Date:   Fri Feb 7 21:34:04 2014 -0800

    Add basic atomic_stats type

    Summary:
    WebScaleSQL Feature: Basic Stats Support

    This is a simple class template that implements an atomic stats variable.

    The focus is on performance, not accuracy.  No set operations are
    guaranteed.  The other operations are all atomic, so values should not
    actually be lost - however, there is no attempt to be consistent in
    reading multiple stats, nor any concern that different threads see any
    consistent view across multiple stats.

    Test Plan:
    This has been tested quite a bit in isolation, and no problems have been
    found.  However, this has never been used in production.  Also, a newer,
    more sophisticated, version of this is already in development.

    It also shows a small perf gain in the larger stats diffs (Table Stats,
    User Stats, etc...), when compared to the built-in MySQL atomics.

    Reviewers: pivanof

    Reviewed By: pivanof

    CC: jtolmer, MarkCallaghan, flamingcow, jeremycole, andrew-ford, inaam-rana, liang.guo.752

    Differential Revision: https://reviews.facebook.net/D16029
    Differential Revision: https://reviews.facebook.net/D16449