Minor - P4 Say you have indices {a: 1} and {b: 1} and the following query:
db.coll.find({c: 1, $or: [{$and: [{a: 1}, {b: 1}]}, {a: 1}]});
Only one plan is generated for this query:
KEEP_MUTATIONS
---filter:
$and
$or
$and
a == 1.0
b == 1.0
a == 1.0
c == 1.0
---fetched = 1
---sortedByDiskLoc = 0
---getSort = []
---Child:
------FETCH
---------filter:
c == 1.0
---------fetched = 1
---------sortedByDiskLoc = 0
---------getSort = []
---------Child:
------------OR
---------------fetched = 0
---------------sortedByDiskLoc = 0
---------------getSort = []
---------------Child 0:
------------------FETCH
---------------------filter:
b == 1.0
---------------------fetched = 1
---------------------sortedByDiskLoc = 1
---------------------getSort = [{ a: 1 }, ]
---------------------Child:
------------------------IXSCAN
---------------------------keyPattern = { a: 1.0 }
---------------------------direction = 1
---------------------------bounds = field #0['a']: [1.0, 1.0]
---------------------------fetched = 0
---------------------------sortedByDiskLoc = 1
---------------------------getSort = [{ a: 1 }, ]
---------------Child 1:
------------------IXSCAN
---------------------keyPattern = { a: 1.0 }
---------------------direction = 1
---------------------bounds = field #0['a']: [1.0, 1.0]
---------------------fetched = 0
---------------------sortedByDiskLoc = 1
---------------------getSort = [{ a: 1 }, ]
However, there are additional plans that have not been enumerated. For example, the first child of the OR stage above could use index {b: 1}. It does not get enumerated because of how we step through the memo (see https://github.com/mongodb/mongo/blob/20a22bdf907a0e2cd60b79f242a7375d84a3ab6a/src/mongo/db/query/plan_enumerator.cpp#L1033). The outer $and only has one "top-level" choice, and we don't consider that there are multiple enumeration choices for the nested $and.
- is related to
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SERVER-13732 Predicates in top-level implicit AND query not considered when generating index access plan for contained OR
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- Closed
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- related to
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- Closed
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