How can we migrate primary shards in the sharded clusters?

1.	How can we migrate primary shards in the sharded clusters?
Answer» Multikey indexes can be used for SUPPORTING efficient querying against array fields. MongoDB creates an index KEY for each element in the array. Note: MongoDB will AUTOMATICALLY create a multikey index if any indexed field is an array, no separate indication required. Consider the startups collection with array of skills *{ _id: 1, name: "XYZ Technology", skills: [ "Big Data", "AI", “Cloud” ] }* Multikey indexes allow to search on the values in the skills array *db.startups.createIndex( { skills : 1 } )* The query db.startups.find( { skills : "AI" } ) will use this index on skills to RETURN the matching document

Answer»

Multikey indexes can be used for SUPPORTING efficient querying against array fields. MongoDB creates an index KEY for each element in the array.

Note: MongoDB will AUTOMATICALLY create a multikey index if any indexed field is an array, no separate indication required.

Consider the startups collection with array of skills

{ _id: 1, name: "XYZ Technology", skills: [ "Big Data", "AI", “Cloud” ] }

Multikey indexes allow to search on the values in the skills array

db.startups.createIndex( { skills : 1 } )

The query db.startups.find( { skills : "AI" } ) will use this index on skills to RETURN the matching document

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