[SERVER-28889] Partial index shouldn't do fetch on conditions that are true by the definition of the index - MongoDB Jira

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db.xxx.ensureIndex({x:1},{partialFilterExpression:{bin:true}})

> db.xxx.find({bin:true,x:1}).explain()

	"queryPlanner" : {

		"plannerVersion" : 1,

		"namespace" : "test.xxx",

		"indexFilterSet" : false,

		"parsedQuery" : {

			"$and" : [

				{"bin" : {"$eq" : true}},

				{"x" : {"$eq" : 1}}

},

		"winningPlan" : {

			"stage" : "FETCH",

			"filter" : {"bin" : {"$eq" : true}},

			"inputStage" : {

				"stage" : "IXSCAN",

				"keyPattern" : {"x" : 1},

				"indexName" : "x_1",

				"isMultiKey" : false,

				"multiKeyPaths" : { "x" : [ ] },

				"isUnique" : false,

				"isSparse" : false,

				"isPartial" : true,

				"indexVersion" : 2,

				"direction" : "forward",

				"indexBounds" : { "x" : [ "[1.0, 1.0]" 	] }

},

		"rejectedPlans" : [ ]

},

	"serverInfo" : {

		"host" : "AD-MAC10G.local",

		"port" : 27017,

		"version" : "3.4.2",

		"gitVersion" : "3f76e40c105fc223b3e5aac3e20dcd026b83b38b"

},

	"ok" : 1

There's no need to do the FETCH with a check on bin:true since that condition is already satisfied by the index partial filterexpression

is duplicated by

SERVER-29247 COUNT_SCAN not used for partial indexes

SERVER-42647 Compound partialFilterExpression not being used - despite correct index chosen

SERVER-44836 count_documents with filter does not use the partialFilterExpression index right when the keys in the filter are indexed

SERVER-32035 Index doesn't cover a query for a partial filter expression index under certain circumstances

is related to

SERVER-26896 Use knowledge about partial index filter expression to determine whether $exists predicate can be covered

SERVER-75025 [CQF] Add test for optimizer-specific fix for SERVER-28889

related to

SERVER-29247 COUNT_SCAN not used for partial indexes

SERVER-55065 Null queries should be covered by index where possible with current index format

SERVER-56020 Unnecessary FETCH stage

SERVER-26580 allow using partial index on query where predicate matches partial filter expression

(1 is related to, 4 related to)

Participants:: Alexander Komyagin, Asya Kamsky, Eliott Coyac, Jacob Botuck, Kyle Suarez, Linus Unnebäck, Milena Ivanova, Ralf Strobel