Details
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New Feature
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Status: Closed
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Major - P3
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Resolution: Done
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None
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Minor Change
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Query 2017-02-13, Query 2017-03-27
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(copied to CRM)
Description
We should extend aggregation explain to report the appropriate information in "executionStats" and "allPlansExecution" explain modes. In "executionStats" mode, the $cursor stage will report detailed information in the same format as used for the explaining other supported commands (find, count, etc.):
> db.c.drop();
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> for (let i = 0; i < 10; i++) { db.c.insert({_id: i, a: 1, b: i}); }
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> db.c.createIndex({a: 1});
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> db.c.createIndex({b: 1});
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> db.c.explain("executionStats").aggregate([{$match: {a: 1, b: {$gt: 3}}}]);
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{
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"stages" : [
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{
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"$cursor" : {
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"query" : {
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"a" : 1,
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"b" : {
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"$gt" : 3
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}
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},
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"queryPlanner" : {
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"plannerVersion" : 1,
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"namespace" : "test.c",
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"indexFilterSet" : false,
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"parsedQuery" : {
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"$and" : [
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{
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"a" : {
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"$eq" : 1
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}
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},
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{
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"b" : {
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"$gt" : 3
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}
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}
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]
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},
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"winningPlan" : {
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"stage" : "FETCH",
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"filter" : {
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"a" : {
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"$eq" : 1
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}
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},
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"inputStage" : {
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"stage" : "IXSCAN",
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"keyPattern" : {
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"b" : 1
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},
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"indexName" : "b_1",
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"isMultiKey" : false,
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"multiKeyPaths" : {
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"b" : [ ]
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},
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"isUnique" : false,
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"isSparse" : false,
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"isPartial" : false,
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"indexVersion" : 2,
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"direction" : "forward",
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"indexBounds" : {
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"b" : [
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"(3.0, inf.0]"
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]
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}
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}
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},
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"rejectedPlans" : [
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{
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"stage" : "FETCH",
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"filter" : {
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"b" : {
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"$gt" : 3
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}
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},
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"inputStage" : {
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"stage" : "IXSCAN",
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"keyPattern" : {
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"a" : 1
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},
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"indexName" : "a_1",
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"isMultiKey" : false,
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"multiKeyPaths" : {
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"a" : [ ]
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},
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"isUnique" : false,
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"isSparse" : false,
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"isPartial" : false,
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"indexVersion" : 2,
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"direction" : "forward",
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"indexBounds" : {
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"a" : [
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"[1.0, 1.0]"
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]
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}
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}
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}
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]
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},
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"executionStats" : {
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"executionSuccess" : true,
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"nReturned" : 6,
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"executionTimeMillis" : 1,
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"totalKeysExamined" : 6,
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"totalDocsExamined" : 6,
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"executionStages" : {
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"stage" : "FETCH",
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"filter" : {
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"a" : {
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"$eq" : 1
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}
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},
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"nReturned" : 6,
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"executionTimeMillisEstimate" : 0,
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"works" : 8,
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"advanced" : 6,
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"needTime" : 0,
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"needYield" : 0,
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"saveState" : 1,
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"restoreState" : 1,
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"isEOF" : 1,
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"invalidates" : 0,
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"docsExamined" : 6,
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"alreadyHasObj" : 0,
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"inputStage" : {
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"stage" : "IXSCAN",
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"nReturned" : 6,
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"executionTimeMillisEstimate" : 0,
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"works" : 7,
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"advanced" : 6,
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"needTime" : 0,
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"needYield" : 0,
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"saveState" : 1,
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"restoreState" : 1,
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"isEOF" : 1,
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"invalidates" : 0,
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"keyPattern" : {
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"b" : 1
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},
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"indexName" : "b_1",
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"isMultiKey" : false,
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"multiKeyPaths" : {
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"b" : [ ]
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},
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"isUnique" : false,
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"isSparse" : false,
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"isPartial" : false,
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"indexVersion" : 2,
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"direction" : "forward",
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"indexBounds" : {
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"b" : [
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"(3.0, inf.0]"
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]
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},
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"keysExamined" : 6,
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"seeks" : 1,
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"dupsTested" : 0,
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"dupsDropped" : 0,
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"seenInvalidated" : 0
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}
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}
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}
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}
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}
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],
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"ok" : 1,
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"operationTime" : Timestamp(0, 0)
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}
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The stages[0].$cursor.executionStats section is entirely new. In "allPlansExecution" mode, the executionStats section is extended with information on all candidate plans evaluated by the plan ranker:
> db.c.explain("allPlansExecution").aggregate([{$match: {a: 1, b: {$gt: 3}}}])
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{
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> db.c.explain("allPlansExecution").aggregate([{$match: {a: 1, b: {$gt: 3}}}])
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{
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"stages" : [
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{
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"$cursor" : {
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"query" : {
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"a" : 1,
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"b" : {
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"$gt" : 3
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}
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},
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"queryPlanner" : {
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"plannerVersion" : 1,
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"namespace" : "test.c",
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"indexFilterSet" : false,
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"parsedQuery" : {
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"$and" : [
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{
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"a" : {
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"$eq" : 1
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}
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},
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{
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"b" : {
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"$gt" : 3
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}
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}
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]
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},
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"winningPlan" : {
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"stage" : "FETCH",
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"filter" : {
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"a" : {
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"$eq" : 1
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}
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},
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"inputStage" : {
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"stage" : "IXSCAN",
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"keyPattern" : {
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"b" : 1
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},
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"indexName" : "b_1",
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"isMultiKey" : false,
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"multiKeyPaths" : {
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"b" : [ ]
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},
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"isUnique" : false,
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"isSparse" : false,
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"isPartial" : false,
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"indexVersion" : 2,
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"direction" : "forward",
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"indexBounds" : {
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"b" : [
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"(3.0, inf.0]"
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]
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}
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}
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},
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"rejectedPlans" : [
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{
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"stage" : "FETCH",
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"filter" : {
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"b" : {
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"$gt" : 3
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}
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},
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"inputStage" : {
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"stage" : "IXSCAN",
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"keyPattern" : {
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"a" : 1
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},
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"indexName" : "a_1",
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"isMultiKey" : false,
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"multiKeyPaths" : {
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"a" : [ ]
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},
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"isUnique" : false,
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"isSparse" : false,
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"isPartial" : false,
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"indexVersion" : 2,
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"direction" : "forward",
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"indexBounds" : {
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"a" : [
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"[1.0, 1.0]"
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]
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}
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}
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}
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]
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},
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"executionStats" : {
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"executionSuccess" : true,
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"nReturned" : 6,
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"executionTimeMillis" : 0,
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"totalKeysExamined" : 6,
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"totalDocsExamined" : 6,
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"executionStages" : {
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"stage" : "FETCH",
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"filter" : {
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"a" : {
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"$eq" : 1
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}
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},
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"nReturned" : 6,
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"executionTimeMillisEstimate" : 0,
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"works" : 8,
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"advanced" : 6,
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"needTime" : 0,
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"needYield" : 0,
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"saveState" : 1,
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"restoreState" : 1,
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"isEOF" : 1,
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"invalidates" : 0,
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"docsExamined" : 6,
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"alreadyHasObj" : 0,
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"inputStage" : {
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"stage" : "IXSCAN",
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"nReturned" : 6,
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"executionTimeMillisEstimate" : 0,
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"works" : 7,
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"advanced" : 6,
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"needTime" : 0,
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"needYield" : 0,
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"saveState" : 1,
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"restoreState" : 1,
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"isEOF" : 1,
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"invalidates" : 0,
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"keyPattern" : {
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"b" : 1
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},
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"indexName" : "b_1",
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"isMultiKey" : false,
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"multiKeyPaths" : {
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"b" : [ ]
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},
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"isUnique" : false,
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"isSparse" : false,
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"isPartial" : false,
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"indexVersion" : 2,
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"direction" : "forward",
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"indexBounds" : {
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"b" : [
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"(3.0, inf.0]"
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]
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},
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"keysExamined" : 6,
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"seeks" : 1,
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"dupsTested" : 0,
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"dupsDropped" : 0,
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"seenInvalidated" : 0
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}
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},
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"allPlansExecution" : [
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{
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"nReturned" : 3,
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"executionTimeMillisEstimate" : 0,
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"totalKeysExamined" : 7,
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"totalDocsExamined" : 7,
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"executionStages" : {
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"stage" : "FETCH",
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"filter" : {
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"b" : {
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"$gt" : 3
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}
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},
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"nReturned" : 3,
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"executionTimeMillisEstimate" : 0,
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"works" : 7,
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"advanced" : 3,
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"needTime" : 4,
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"needYield" : 0,
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"saveState" : 1,
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"restoreState" : 1,
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"isEOF" : 0,
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"invalidates" : 0,
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"docsExamined" : 7,
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"alreadyHasObj" : 0,
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"inputStage" : {
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"stage" : "IXSCAN",
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"nReturned" : 7,
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"executionTimeMillisEstimate" : 0,
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"works" : 7,
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"advanced" : 7,
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"needTime" : 0,
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"needYield" : 0,
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"saveState" : 1,
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"restoreState" : 1,
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"isEOF" : 0,
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"invalidates" : 0,
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"keyPattern" : {
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"a" : 1
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},
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"indexName" : "a_1",
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"isMultiKey" : false,
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"multiKeyPaths" : {
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"a" : [ ]
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},
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"isUnique" : false,
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"isSparse" : false,
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"isPartial" : false,
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"indexVersion" : 2,
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"direction" : "forward",
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"indexBounds" : {
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"a" : [
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"[1.0, 1.0]"
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]
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},
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"keysExamined" : 7,
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"seeks" : 1,
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"dupsTested" : 0,
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"dupsDropped" : 0,
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"seenInvalidated" : 0
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}
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}
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},
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{
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"nReturned" : 6,
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"executionTimeMillisEstimate" : 0,
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"totalKeysExamined" : 6,
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"totalDocsExamined" : 6,
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"executionStages" : {
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"stage" : "FETCH",
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"filter" : {
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"a" : {
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"$eq" : 1
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}
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},
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"nReturned" : 6,
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"executionTimeMillisEstimate" : 0,
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"works" : 7,
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"advanced" : 6,
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"needTime" : 0,
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"needYield" : 0,
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"saveState" : 1,
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"restoreState" : 1,
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"isEOF" : 1,
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"invalidates" : 0,
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"docsExamined" : 6,
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"alreadyHasObj" : 0,
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"inputStage" : {
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"stage" : "IXSCAN",
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"nReturned" : 6,
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"executionTimeMillisEstimate" : 0,
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"works" : 7,
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"advanced" : 6,
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"needTime" : 0,
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"needYield" : 0,
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"saveState" : 1,
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"restoreState" : 1,
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"isEOF" : 1,
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"invalidates" : 0,
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"keyPattern" : {
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"b" : 1
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},
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"indexName" : "b_1",
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"isMultiKey" : false,
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"multiKeyPaths" : {
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"b" : [ ]
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},
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"isUnique" : false,
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"isSparse" : false,
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"isPartial" : false,
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"indexVersion" : 2,
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"direction" : "forward",
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"indexBounds" : {
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"b" : [
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"(3.0, inf.0]"
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]
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},
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"keysExamined" : 6,
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"seeks" : 1,
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"dupsTested" : 0,
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"dupsDropped" : 0,
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"seenInvalidated" : 0
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}
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}
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}
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]
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}
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}
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}
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],
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"ok" : 1,
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"operationTime" : Timestamp(0, 0)
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}
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Here, the stages[0].$cursor.executionStats.allPlansExecution section is entirely new. This is implemented by allowing the explain command to accept a nested aggregate command:
{explain: {aggregate: ...}, verbosity: "allPlansExecution"}
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The aggregate command's explain parameter is still supported, as in {aggregate: "myCollection", pipeline: [], explain: true}. However, the explain command format is preferred. It is illegal to combine the two formats, as in
{explain: {aggregate: "myCollection", pipeline: [], explain: true}, verbosity: "allPlansExecution"}
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Finally, since the explain command has never supported readConcern or writeConcern, we have made it an error to use readConcern or writeConcern in combination with the aggregate command explain flag. All of the following examples are illegal:
{aggregate: "myCollection", pipeline: [{$out: "foo"}], explain: true, writeConcern: {w: 1}}
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{explain: {aggregate: "myCollection", pipeline: [{$out: "foo"}]}, writeConcern: {w: 1}}
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{aggregate: "myCollection", pipeline: [{$out: "foo"}], explain: true, readConcern: {level: "majority"}}
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{explain: {aggregate: "myCollection", pipeline: [{$out: "foo"}]}, readConcern: {level: "majority"}}
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This is a minor breaking change in 3.6 which will have to be accommodated by drivers.
Note that aggregation stages other than $cursor do not currently report execution stats. Implementing this is further work tracked by SERVER-21784.
Attachments
Issue Links
- is depended on by
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DOCS-11777 db.collection.explain("verbosity") now supported for aggregation
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- Closed
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SERVER-21784 Track 'nReturned' and 'executionTimeMillis' execution stats for each aggregation pipeline stage and expose via explain
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- Closed
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- is related to
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- Waiting (Blocked)
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DRIVERS-375 Aggregate command's explain flag cannot be used in combination with readConcern or writeConcern
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- Closed
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- Closed
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- related to
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- Closed
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- Closed
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- Closed
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