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Operating System:
ALL
Steps To Reproduce:
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db.a.drop(); db.a.createIndex( { b: 1, c: 1 }, { partialFilterExpression: { b: { $exists: true } } }); db.a.createIndex( { a: 1, c: 1 }, { partialFilterExpression: { a: { $exists: true } } }); db.a.explain().find({ $or: [ { a: 0 }, { b: 0 }, ], c: 1,});

Produces two index scans, one restricted only on the `a` field, the other only on the `b` field. The `c` field is not restricted, even though it can be.
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db.a.drop(); db.a.createIndex( { b: 1, c: 1 }, { partialFilterExpression: { b: { $exists: true } } }); db.a.createIndex( { a: 1, c: 1 }, { partialFilterExpression: { a: { $exists: true } } }); db.a.explain().find({ $or: [ { a: 0 }, { b: 0 }, ], c: 1,}); Produces two index scans, one restricted only on the `a` field, the other only on the `b` field. The `c` field is not restricted, even though it can be.
Confidence Status:
None
Work Order:
0

$or queries using partial indices produce inefficient index scans.

is related to

SERVER-18491 Add support for $or query to be answered by partial index

SERVER-17854 Allow $or predicates to be indexed by partial indexes