Details
Minor - P4 Description
There have been a few behavior changes in v2.6 related to negations. These should probably go into the 2.6 release notes? See SERVER-13324 and SERVER-12532 or come talk to me for details.
1) In 2.4 it is possible to get different results for negations depending on whether or not an indexed plan is used:
> t.drop()
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true
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> t.save({a: 1})
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> t.save({b: 1})
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> t.find({a: {$not: {$gt: 3}}})
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{ "_id" : ObjectId("5330803029b74d493d375e46"), "a" : 1 }
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{ "_id" : ObjectId("5330803529b74d493d375e47"), "b" : 1 }
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> t.ensureIndex({a: 1})
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> t.find({a: {$not: {$gt: 3}}})
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{ "_id" : ObjectId("5330803029b74d493d375e46"), "a" : 1 }
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In 2.6, the results will always be the same regardless of whether or not there is an index:
> t.drop()
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true
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> t.save({a: 1})
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WriteResult({ "nInserted" : 1 })
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> t.save({b: 1})
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WriteResult({ "nInserted" : 1 })
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> t.find({a: {$not: {$gt: 3}}})
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{ "_id" : ObjectId("5330808b3a40985f27706d1e"), "a" : 1 }
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{ "_id" : ObjectId("5330808d3a40985f27706d1f"), "b" : 1 }
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> t.ensureIndex({a: 1})
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{
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"createdCollectionAutomatically" : false,
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"numIndexesBefore" : 1,
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"numIndexesAfter" : 2,
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"ok" : 1
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}
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> t.find({a: {$not: {$gt: 3}}})
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{ "_id" : ObjectId("5330808d3a40985f27706d1f"), "b" : 1 }
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{ "_id" : ObjectId("5330808b3a40985f27706d1e"), "a" : 1 }
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2) Negation predicates will no longer use sparse indices. This is necessary in order to preserve the invariant from (1), namely that a negation query should return the same results for indexed and unindexed plans. See SERVER-13324.
Attachments
Issue Links
- is related to
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SERVER-12532 Negate index bounds for $not instead of defaulting to a collection scan
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- Closed
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- Closed
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