Details
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Improvement
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Status: Backlog
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Major - P3
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Resolution: Unresolved
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5.1.0
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None
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None
Description
MongoDB version 5.X introduced the slot-based execution (SBE) query engine. Running an explain() plan on a query that is using SBE provides an output like this:
PRIMARY> db.test1.explain().find({a:1})
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{
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"explainVersion" : "2",
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"queryPlanner" : {
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"namespace" : "test.test1",
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"indexFilterSet" : false,
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"parsedQuery" : {
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"a" : {
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"$eq" : 1
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}
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},
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"queryHash" : "4B53BE76",
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"planCacheKey" : "2DEF680C",
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"maxIndexedOrSolutionsReached" : false,
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"maxIndexedAndSolutionsReached" : false,
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"maxScansToExplodeReached" : false,
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"winningPlan" : {
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"queryPlan" : {
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"stage" : "FETCH",
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"planNodeId" : 2,
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"inputStage" : {
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"stage" : "IXSCAN",
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"planNodeId" : 1,
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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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"slotBasedPlan" : {
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"slots" : "$$RESULT=s13 $$RID=s14 env: { s2 = Nothing (SEARCH_META), s1 = TimeZoneDatabase(Canada/Yukon...America/Rainy_River) (timeZoneDB), s4 = 1637002207166 (NOW), s3 = Timestamp(1637002203, 1) (CLUSTER_TIME) }",
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"stages" : "[2] nlj [] [s9, s5, s6, s7, s8] \n left \n [1] nlj [s6, s8] [s10, s11] \n left \n [1] project [s6 = \"a_1\", s8 = {\"a\" : 1}, s10 = KS(2B020104), s11 = KS(2B02FE04)] \n [1] limit 1 \n [1] coscan \n right \n [1] project [s5 = s12] \n [1] ixseek s10 s11 s7 s9 s12 [] @\"2c41ddb0-4c30-488c-a2dd-11240fa088e8\" @\"a_1\" true \n \n \n right \n [2] limit 1 \n [2] seek s9 s13 s14 s5 s6 s7 s8 [] @\"2c41ddb0-4c30-488c-a2dd-11240fa088e8\" true false \n \n"
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}
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},
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"rejectedPlans" : [ ]
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},
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"command" : {
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"find" : "test1",
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"filter" : {
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"a" : 1
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},
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"$db" : "test"
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},
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"serverInfo" : {
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"host" : "atlas-9ev3lx-shard-00-02.oz4jm.mongodb.net",
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"port" : 27017,
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"version" : "5.1.0",
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"gitVersion" : "2454bbc8c20c8d6d6d9590a66e939d568b9e7222"
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},
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"serverParameters" : {
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"internalQueryFacetBufferSizeBytes" : 104857600,
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"internalQueryFacetMaxOutputDocSizeBytes" : 104857600,
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"internalLookupStageIntermediateDocumentMaxSizeBytes" : 104857600,
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"internalDocumentSourceGroupMaxMemoryBytes" : 104857600,
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"internalQueryMaxBlockingSortMemoryUsageBytes" : 104857600,
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"internalQueryProhibitBlockingMergeOnMongoS" : 0,
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"internalQueryMaxAddToSetBytes" : 104857600,
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"internalDocumentSourceSetWindowFieldsMaxMemoryBytes" : 104857600
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},
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"ok" : 1,
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"$clusterTime" : {
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"clusterTime" : Timestamp(1637002203, 1),
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"signature" : {
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"hash" : BinData(0,"qMUDrkJ1eQV3Y+0cDewpDaiM+s0="),
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"keyId" : NumberLong("7029021327763701764")
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}
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},
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"operationTime" : Timestamp(1637002203, 1)
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}
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While the "winningPlan"Â section as well as other sections above are useful, the "slotBasedPlan" section cannot be comprehended easily:
"slotBasedPlan" : {
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"slots" : "$$RESULT=s13 $$RID=s14 env: { s2 = Nothing (SEARCH_META), s1 = TimeZoneDatabase(Canada/Yukon...America/Rainy_River) (timeZoneDB), s4 = 1637002207166 (NOW), s3 = Timestamp(1637002203, 1) (CLUSTER_TIME) }",
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"stages" : "[2] nlj [] [s9, s5, s6, s7, s8] \n left \n [1] nlj [s6, s8] [s10, s11] \n left \n [1] project [s6 = \"a_1\", s8 = {\"a\" : 1}, s10 = KS(2B020104), s11 = KS(2B02FE04)] \n [1] limit 1 \n [1] coscan \n right \n [1] project [s5 = s12] \n [1] ixseek s10 s11 s7 s9 s12 [] @\"2c41ddb0-4c30-488c-a2dd-11240fa088e8\" @\"a_1\" true \n \n \n right \n [2] limit 1 \n [2] seek s9 s13 s14 s5 s6 s7 s8 [] @\"2c41ddb0-4c30-488c-a2dd-11240fa088e8\" true false \n \n"
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}
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Hence, this request is for improving the readability of the explain plans in 5.X and above that use the slot-based execution query engine.