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Type:
New Feature
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Resolution: Unresolved
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Priority:
Minor - P4
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None
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Affects Version/s: None
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Component/s: Querying
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None
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Query Optimization
Currently there are three explain modes:
- queryPlanner - generates plans, selects the best one
- executionStats - generates plans, selects the best one, runs the winner and reports on its execution
- allPlansExecution - generates plans, selects the best one, runs the winner, reports on the execution of the winner and the losing candidate plans
I propose adding a fourth mode called "listPlans". This mode would generate candidate plans, but do nothing more. It will not perform plan selection, and therefore cannot tell you which plan will be executed. However, it would run almost instantaneously because it does not need to use the query execution machinery at all.
Example:
> db.test.find({a: 1}).explain("listPlans")
{
"queryPlanner" : {
"plannerVersion" : 1,
"namespace" : "test.test",
"indexFilterSet" : false,
"parsedQuery" : {
"a" : {
"$eq" : 1
}
},
"plans" : [
{
"stage" : "FETCH",
"inputStage" : {
"stage" : "IXSCAN",
"keyPattern" : {
"a" : 1
},
"indexName" : "a_1",
"isMultiKey" : false,
"direction" : "forward",
"indexBounds" : {
"a" : [
"[1.0, 1.0]"
]
}
}
},
{
"stage" : "FETCH",
"inputStage" : {
"stage" : "IXSCAN",
"keyPattern" : {
"a" : 1,
"b": 1
},
"indexName" : "a_1_b_1",
"isMultiKey" : false,
"direction" : "forward",
"indexBounds" : {
"a" : [
"[1.0, 1.0]"
],
"b" : [
"[MinKey, MaxKey]"
]
}
}
}]
},
"serverInfo" : {
"host" : "dstorch-desktop",
"port" : 27017,
"version" : "2.8.0-rc6-pre-",
"gitVersion" : "89ddf2d90625a7738b8e48dce1a5776942603d27"
},
"ok" : 1
}
- is duplicated by
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SERVER-41343 Add parameter for explain() to bound the trial phase
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- Closed
-