Comment 4 for bug 1193906

Reviewed: https://review.openstack.org/39463
Committed: http://github.com/openstack/ceilometer/commit/8ddafe40532619bbb3c4055be3f74471f0dcc518
Submitter: Jenkins
Branch: stable/grizzly

commit 8ddafe40532619bbb3c4055be3f74471f0dcc518
Author: terriyu <email address hidden>
Date: Tue Jul 9 02:29:36 2013 +0000

    Add index for db.meter by descending timestamp

    Fixes bug #1193906

    Added an index for db.meter to sort by descending time stamp for class
    Connection in ceilometer/storage/impl_mongodb.py

    ensure_index() is used rather than create_index() to be more efficient.

    This index is needed because get_samples() in
    ceilometer/storage/impl_mongodb.py sorts by descending timestamp. Without an
    index, MongoDB will fail to sort if the database is too large.

    Change-Id: I23070f153ce03a8d6d8c9f17f05e2d5dae38647e
    (cherry picked from commit e984f28b00e3a073c176f6435507f5bce1c82d30)