Revision as of 16:00, 6 May 2014

Architecture

REST resource

The new solution includes new REST resources for provide complex queries for sample statistics:

AlarmStatistics

Example:

{ "aggregate": {"count": 19.0},
  "duration": 328.478029,
  "duration_start": "2014-01-31T10:00:41.823919",
  "duration_end": "2014-01-31T10:06:10.301948",
  "period": 900,
  "period_start": "2014-01-31T10:00:00",
  "period_end": "2014-01-31T10:15:00",
  "groupby": {"project_id": "061a5c91811e4044b7dc86c6136c4f99"}
}

As new resource is defined, the simple statistics query support remained as it is now, which means that the API is backward compatible and also a new query grammar could be defined without limitations.

Filter Expression Language

The same expression language is used as in Ceilometer/ComplexFilterExpressionsInAPIQueries#Filter_Expression_Language

Supported DB drivers

Planned to be supported:

• SqlAlchemy
• MongoDB

API examples

Consider a requirement for determining, for some tenant, the number of distinct instances (cardinality) as well as the total number of instance samples (count). You might also want to see this information with 15 minute long intervals. Then, using current API the query would look like the following:

GET /v2/meters/instance/statistics?aggregate.func=cardinality
                                  &aggregate.param=resource_id
                                  &aggregate.func=count
                                  &groupby=project_id&period=900

With the new API it would look like the following

POST /v2/query/samples/statistics

With the body:

{
filter: {"=": {"counter_name": "instance"}},
aggregates: [{"func": "cardinality", "param": ["resource_id"]}, {"func": "count", "param": []}],
groupby: ["project_id"],
period: 900,
}

You can also limit and order the result with the following extended body:

{
filter: {"=": {"counter_name": "instance"}},
aggregates: [{"func": "cardinality", "param": ["resource_id"]}, {"func": "count", "param": []}],
groupby: ["project_id"],
period: 900,
orderby: [{"count": "ASC"}, {"cardinality/resource_id": "DESC"}],
limit: 10
}

Possible extensions

Request: Return the last sample for each resource for a meter Problems:

• The "last" function is not a valid aggregate function as it does not generate a single field for every row in the result. We can fix that by changing the request to "Return the last 'field_name' for each resource for a meter". Where 'field_name' is a field of the sample (e.g. counter_volume). This way last(field_name) becomes a valid aggregate function.
• SQL does not provide last(field_name) kind of aggregate out of the box. To implement it we need to issue a subquery.