Mongodb聚合框架: Does $group use index?

Question

我正在尝试将聚合框架与 $match 和 $group 阶段一起使用。 $group 阶段是否使用索引数据？我正在使用最新的可用 mongodb 版本 - 2.5.4

Answer 1

$group 不使用索引数据。

来自 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.