performance - Mongodb Aggregation Framework: Does $group use index?

Question

I'm trying to use aggregation framework with $match and $group stages. Does $group stage use index data? I'm using latest available mongodb version - 2.5.4

Answer 1

$group does not use index data.

From the mongoDB docs:

The $match and $sort pipeline operators can take advantage of an index when they occur at the beginning of the pipeline.

The $geoNear pipeline operator takes advantage of a geospatial index. When using $geoNear, the $geoNear pipeline operation must appear as the first stage in an aggregation pipeline.