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Created November 4, 2015 18:17
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Fighting with mongo's query planner
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sample.md

Index

db.{collection}.ensureIndex({ fieldA: 1, "nested.B": 1, "nested.C": 1 })

Bad query

db.{collection}.find({ fieldA: "abc", "nested.B": "123", "nested.C": "456"})

Only uses first two index fields and then individually scans all matching items for "nested.C": 1.

Good query

db.{collection}.find({ fieldA: "abc", "nested": { $elemMatch: { "B": "123", "C": "456" } })

Actually uses all three index fields.

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