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Type:
Improvement
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Resolution: Unresolved
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Priority:
Major - P3
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Affects Version/s: None
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Component/s: None
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Query Optimization
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3
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Consider this example:
db.test.createIndex({"a.$**": 1})
// IXSCAN with "$_path" : ["[\"a.b\", \"a.b\"]", "[\"a.b.\", \"a.b/\")"] + FETCH without filter
db.test.find({'a.b': {$exists: true}}).explain()
db.test.dropIndexes()
db.test.createIndex({"a.$**": 1, b: 1})
// IXSCAN with "$_path" : ["[\"a.b\", \"a.b\"]", "[\"a.b.\", \"a.b/\")"] + FETCH with {$exists: true}
db.test.find({'a.b': {$exists: true}}).explain()
In the above example, this behavior is unlikely to cause significant issues because the index scan already filters out all keys where `a.b` doesn't exist. However, when the wildcard part doesn't come first in the compound index, this behavior can trigger the limitation described in SERVER-83322 and prevent $exists: true from being evaluated using the CWI.
- related to
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- Backlog
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