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Why is MongoDB not using index?
The reason is the way that MongoDB creates compound indexes. If you skip the leading member of the index, then the index traversal will have to skip lots of blocks. If that performance is slow, then the query optimizer will choose to use a full-collection scan rather than use the index.
Does MongoDB aggregate use index?
$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.
Which type of indexes does MongoDB support?
To query geospatial data, MongoDB supports two types of indexes – 2d indexes and 2d sphere indexes. 2d indexes use planar geometry when returning results and 2dsphere indexes use spherical geometry to return results.
Is find faster than aggregate?
Without seeing your data and your query it is difficult to answer why aggregate+sort is faster than find+sort. A well indexed(Indexing that suits your query) data will always yield faster results on your find query.
Does aggregation use index?
If the added $match stage is at the start of a pipeline, the aggregation can use an index as well as query the collection to limit the number of documents that enter the pipeline.
Can we create multiple index on same column mysql?
Yes, it can have an effect. Of course the two indexes take extra space on disk and also in memory if they are used. But they also cause the query optimizer to do more work to calculate the benefit of each index during every SELECT. The more indexes you have, the more cases it has to compare.
When to use the$ setissubset operator in MongoDB?
The following operation uses the $setIsSubset operator to determine if the A array is a subset of the B array: The operation returns the following results: © MongoDB, Inc 2008-present. MongoDB, Mongo, and the leaf logo are registered trademarks of MongoDB, Inc.
What happens if an array contains duplicates in MongoDB?
If an array contains duplicate entries, $setIsSubset ignores the duplicate entries. $setIsSubset ignores the order of the elements. If a set contains a nested array element, $setIsSubset does not descend into the nested array but evaluates the array at top-level. Consider an experiments collection with the following documents:
What kind of syntax does$ setissubset use?
$setIsSubset has the following syntax: The arguments can be any valid expression as long as they each resolve to an array. For more information on expressions, see Expressions. $setIsSubset performs set operation on arrays, treating arrays as sets.