Details
Description
The query shape serialization mechanism will map distinct query shapes to the same plan cache key. This can cause cache thrashing for the plan cache.
The encoding of plan cache keys for queries needs to (1) group lists, (2) perform escaping, and (3/4) delimit the query/sort/projection sections. See examples below.
// 1.
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db.foo.find({$or:[{a:1},{b:1},{c:1}],d:1}) // plan cache key = anoreqaeqbeqceqd |
db.foo.find({$or:[{a:1},{b:1}],c:1,d:1}) // plan cache key = anoreqaeqbeqceqd |
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// 2.
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db.foo.find({a:1,b:1,c:1}) // plan cache key = aneqaeqbeqc |
db.foo.find({a:1,beqc:1}) // plan cache key = aneqaeqbeqc |
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// 3.
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db.foo.find({a:1},{a:NumberInt(1)}) // plan cache key = eqap1a |
db.foo.find({ap1a:1}) // plan cache key = eqap1a |
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// 4.
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db.foo.find({a:1}).sort({b:1}) // plan cache key = eqaab |
db.foo.find({aab:1}) // plan cache key = eqaab |
Attachments
Issue Links
- related to
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SERVER-17158 sort component of internal plan cache key syntax is ambiguous
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- Closed
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