Why _id index in a sharded cluster is recommended to be used as a shar

1.	Why _id index in a sharded cluster is recommended to be used as a shard key?
Answer» All the 3 projection operators, i.e., $, $elemMatch, $slice are USED for MANIPULATING arrays. They are used to LIMIT the contents of an array from the query results. For example, *db.startups.find( {}, { SKILLS: { $slice: 2 } } )* selects the first 2 items from the skills array for each document returned.

Why _id index in a sharded cluster is recommended to be used as a shard key?

Answer»

All the 3 projection operators, i.e., $, $elemMatch, $slice are USED for MANIPULATING arrays. They are used to LIMIT the contents of an array from the query results.

For example, db.startups.find( {}, { SKILLS: { $slice: 2 } } ) selects the first 2 items from the skills array for each document returned.

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db.employee.find({"employeeid" : {"$gte" : 15000, "$lte" : 70000}});

Why _id index in a sharded cluster is recommended to be used as a shard key?

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