How to create a compound index in MongoDB

Question

Recently I have created a collection that contains a limited number (<5 by now) of kind of data, I created the collection with entity_type and entity_id, as following shown

+-------------+-----------+---------+------
| entity_type | entity_id | date    | ...
+-------------+-----------+---------+------

And since the query for the latest records are more frequency. So I created the following compound index (note that the entity_id is not globally unique)

[('date': -1), ('entity_type': 1), ('entity_id': 1)]

However, I am not sure if such index is okay since someone said that the index should not created on a field (here it is entity_type) which only has limited values.

Since your index includes other fields as well, which look like they will have a high cardinality (many possible values), I think this compound index will be fine. — PaulMcG
– PaulMcG, Commented May 26, 2016 at 5:30

Sandesh · Accepted Answer · 2016-05-26 03:22:13Z

1

It's recommended to create mongodb index on fields which ensures high selectivity.

So if entity_type column contains limited values, I would suggest to remove this column from compound index.

MongoDB Index Selectivity

answered May 26, 2016 at 3:22

Sandesh

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1 Comment

Jacky Wang Over a year ago

The link you given said

A better strategy, depending on your queries, would be to create a compound index that includes the low-selectivity field and another field

. So the above index is also okay even with entity_type included.

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