Aggregate - Is $project really effective in a two step ($match->$group) aggregate operation?

[Manoj Vivek]

Hi All,

The question here is, Will $project really necessary for in a two step aggregate with $match and $group.

Operation 1 : $match->$group

Operation 2 : $match->$project->$group

Will operation 2 be faster and efficient than Operation 1?

I see, Operation 2 with $project is unnecessary as it has only one step after the $project. no?

-Manoj Vivek

[Asya Kamsky]

You do not need project unless it's actually computing a new field.

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[Manoj Vivek]

We dont need $project to reduce the size of aggregate document?

[Asya Kamsky]

No, you don't, the aggregation framework scans the full pipeline and
only passes through the fields that are actually going to be
needed/used in later stages.

Asya

On Wed, Apr 9, 2014 at 11:07 AM, Manoj Vivek <p.mano...@gmail.com> wrote:
> We dont need $project to reduce the size of aggregate document?
>

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