Details
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Improvement
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Status: Closed
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Major - P3
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Resolution: Fixed
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None
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None
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Fully Compatible
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Query 2020-09-07, Query 2020-09-21, Query 2020-10-05, Query 2020-10-19
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(copied to CRM)
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0
Description
Not sure why we don't do this:
db.skip.explain().aggregate([{$match:{a:{$gte:7}}},{$sort:{a:1}},{$skip:2}])
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{
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"stages" : [
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{
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"$cursor" : {
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"query" : {
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"a" : {
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"$gte" : 7
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}
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},
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"sort" : {
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"a" : 1
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},
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"queryPlanner" : {
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"plannerVersion" : 1,
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"namespace" : "agg.skip",
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"indexFilterSet" : false,
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"parsedQuery" : {
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"a" : {
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"$gte" : 7
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}
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},
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"winningPlan" : {
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"stage" : "FETCH",
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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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"[7.0, 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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}
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},
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{
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"$skip" : NumberLong(2)
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}
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],
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"ok" : 1
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}
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> db.skip.explain().aggregate([{$match:{a:{$gte:7}}},{$sort:{a:1}},{$skip:2},{$limit:1}])
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{
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"stages" : [
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{
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"$cursor" : {
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"query" : {
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"a" : {
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"$gte" : 7
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}
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},
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"sort" : {
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"a" : 1
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},
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"limit" : NumberLong(3),
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"queryPlanner" : {
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"plannerVersion" : 1,
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"namespace" : "agg.skip",
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"indexFilterSet" : false,
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"parsedQuery" : {
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"a" : {
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"$gte" : 7
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}
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},
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"winningPlan" : {
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"stage" : "FETCH",
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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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"[7.0, 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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}
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},
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{
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"$skip" : NumberLong(2)
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}
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],
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"ok" : 1
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}
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In the first case we don't push anything down, in the second case we push down limit(3) - sum of skip and limit values - but in both cases we then do the skip in agg in the next stage.
Attachments
Issue Links
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- Closed
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