Comment 8 for bug 1506738

Reviewed: https://review.openstack.org/239429
Committed: https://git.openstack.org/cgit/openstack/ceilometer/commit/?id=16af61a0de1ae1d6165babac0f026c4d4c3b5cb9
Submitter: Jenkins
Branch: stable/liberty

commit 16af61a0de1ae1d6165babac0f026c4d4c3b5cb9
Author: ZhiQiang Fan <email address hidden>
Date: Fri Oct 16 02:45:45 2015 -0700

    avoid generate temporary table when query samples

    Currently, when we call query-samples API, for SQL backend, we do
    an inner join to get a temporary table, then apply filters, orderby
    and limit options on it. Such implementation will drain disk space
    or cause timeout exception when data set is growing, even with specified
    limit and filters.

    This patch applies filters and limit on the inner join itself, and
    uses a fake mapper object instead of temporary table to suit current
    query transformer.

    Change-Id: I261a2dd362ed51c16a6fa191dadcce1b45fce2e4
    Closes-Bug: #1506738
    (cherry picked from commit b9bf5f1f571f21aee4347c80a5a7ac8a1c456e45)