Non-Indexed match query should be before or after project?

Pavel_Duchovny · January 7, 2021, 6:08am

Welcome to MongoDB community!

First if you have a set of “and” expressions that could be placed in first stage you should do that to pass as minimum data to the next stage as possible. Now if this query is often reoccurring why not to have a compound index on all 3 fields? This will speedup the query regardless of doc access or not.

Additionally, the order of the fields in the index matter. We call it Equility Sort and Range order.

So in your case n optimal index will be {field1: 1, ts : 1, field2 : 1}.

Additionally if an index can cover all return data it can be a covered query and speed performance so having all fields can help avoid document scans.

I suggest to read the following material:

Thanks
Pavel