Comment 8 for bug 1506877

Reviewed: https://review.fuel-infra.org/10641
Submitter: Vitaly Sedelnik <email address hidden>
Branch: openstack-ci/fuel-6.1/2014.2

Commit: 2d7821db1699da1a688c605fdd91aea26e37c136
Author: Ilya Tyaptin <email address hidden>
Date: Fri Oct 30 10:54:10 2015

[MongoDB] Use a aggregate pipeline in statistics

Currently, we use a native mapreduce jobs for highload requests
in MongoDb backend, but this approach have insufficient performance.
For example, at test environment mapreduce job processes a 10k samples/sec.
It's not good result for big collections.
Aggregation framework has a better performance and enough syntax
for our needs. At test environment it shows a improving "statistics" request
performance up to 10 times.

Closes-Bug: #1506877
Implements: blueprint mongodb-aggregation-pipeline
Change-Id: I60040b4472529d460f03cc4d1b55d883ea339124
(cherry-picked from c41a8856b98a435bc9af4ea80d42f5d8139b7fe9)