[SERVER-41263] Disallow the empty string as an index key type - MongoDB

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Type: Bug
Status: Closed
Priority: Major - P3
Resolution: Fixed
Affects Version/s: None
Fix Version/s: 4.3.1, 4.2.3
Component/s: Indexing
Labels:
- neweng
- schwerin-mms-impact

Backwards Compatibility:
Minor Change
Operating System:
ALL
Backport Requested:

v4.2

Steps To Reproduce:

Hide

db.repro.createIndex({x:""})

Outputs:

> db.repro.createIndex({x:""})

	"createdCollectionAutomatically" : true,

	"numIndexesBefore" : 1,

	"numIndexesAfter" : 2,

	"ok" : 1

A few additional lines from 4.1.10:

> db.version()

4.1.10

> db.repro.createIndex({x:""})

	"createdCollectionAutomatically" : true,

	"numIndexesBefore" : 1,

	"numIndexesAfter" : 2,

	"ok" : 1

> db.repro.createIndex({x:1})

	"createdCollectionAutomatically" : false,

	"numIndexesBefore" : 2,

	"numIndexesAfter" : 3,

	"ok" : 1

> db.repro.getIndices()

		"v" : 2,

		"key" : {

			"_id" : 1

},

		"name" : "_id_",

		"ns" : "repo.repro"

},

		"v" : 2,

		"key" : {

			"x" : ""

},

		"name" : "x_",

		"ns" : "repo.repro"

},

		"v" : 2,

		"key" : {

			"x" : 1

},

		"name" : "x_1",

		"ns" : "repo.repro"

Show

db.repro.createIndex({x:""}) Outputs: > db.repro.createIndex({x:""}) { "createdCollectionAutomatically" : true, "numIndexesBefore" : 1, "numIndexesAfter" : 2, "ok" : 1 } A few additional lines from 4.1.10 : > db.version() 4.1.10 > db.repro.createIndex({x:""}) { "createdCollectionAutomatically" : true, "numIndexesBefore" : 1, "numIndexesAfter" : 2, "ok" : 1 } > db.repro.createIndex({x:1}) { "createdCollectionAutomatically" : false, "numIndexesBefore" : 2, "numIndexesAfter" : 3, "ok" : 1 } > db.repro.getIndices() [ { "v" : 2, "key" : { "_id" : 1 }, "name" : "_id_", "ns" : "repo.repro" }, { "v" : 2, "key" : { "x" : "" }, "name" : "x_", "ns" : "repo.repro" }, { "v" : 2, "key" : { "x" : 1 }, "name" : "x_1", "ns" : "repo.repro" } ]

Sprint:
Query 2019-06-17
Case:

Description

At present it is possible to generate an index with an empty string as the key type (eg a definition of {x:""}). The optimizer seems to be able to use this index when the key is a predicate in the query:

> db.repro.find({x:123}).explain()

	"queryPlanner" : {

		"plannerVersion" : 1,

		"namespace" : "repro.repro",

		"indexFilterSet" : false,

		"parsedQuery" : {

			"x" : {

				"$eq" : 123

},

		"queryHash" : "716F281A",

		"planCacheKey" : "0FA0E5FD",

		"winningPlan" : {

			"stage" : "FETCH",

			"inputStage" : {

				"stage" : "IXSCAN",

				"keyPattern" : {

					"x" : ""

},

				"indexName" : "x_",

				"isMultiKey" : false,

				"multiKeyPaths" : {

					"x" : [ ]

},

				"isUnique" : false,

				"isSparse" : false,

				"isPartial" : false,

				"indexVersion" : 2,

				"direction" : "forward",

				"indexBounds" : {

					"x" : [

						"[123.0, 123.0]"

},

		"rejectedPlans" : [ ]

},

	"serverInfo" : {

		"host" : "Chriss-MacBook-Pro.local",

		"port" : 27017,

		"version" : "4.1.10",

		"gitVersion" : "8cdc51e7810f7fd8898a4c60b935e389f04659ee"

},

	"ok" : 1

However it is unable to use the index to sort:

> db.repro.find({x:123}).sort({x:1}).explain()

	"queryPlanner" : {

		"plannerVersion" : 1,

		"namespace" : "repro.repro",

		"indexFilterSet" : false,

		"parsedQuery" : {

			"x" : {

				"$eq" : 123

},

		"queryHash" : "87B348CE",

		"planCacheKey" : "F46EA305",

		"winningPlan" : {

			"stage" : "FETCH",

			"inputStage" : {

				"stage" : "SORT",

				"sortPattern" : {

					"x" : 1

},

				"inputStage" : {

					"stage" : "SORT_KEY_GENERATOR",

					"inputStage" : {

						"stage" : "IXSCAN",

						"keyPattern" : {

							"x" : ""

},

						"indexName" : "x_",

						"isMultiKey" : false,

						"multiKeyPaths" : {

							"x" : [ ]

},

						"isUnique" : false,

						"isSparse" : false,

						"isPartial" : false,

						"indexVersion" : 2,

						"direction" : "forward",

						"indexBounds" : {

							"x" : [

								"[123.0, 123.0]"

},

		"rejectedPlans" : [ ]

},

	"serverInfo" : {

		"host" : "Chriss-MacBook-Pro.local",

		"port" : 27017,

		"version" : "4.1.10",

		"gitVersion" : "8cdc51e7810f7fd8898a4c60b935e389f04659ee"

},

	"ok" : 1

> db.repro.find().sort({x:1}).explain()

	"queryPlanner" : {

		"plannerVersion" : 1,

		"namespace" : "repro.repro",

		"indexFilterSet" : false,

		"parsedQuery" : {

},

		"queryHash" : "B7791BAD",

		"planCacheKey" : "B7791BAD",

		"winningPlan" : {

			"stage" : "SORT",

			"sortPattern" : {

				"x" : 1

},

			"inputStage" : {

				"stage" : "SORT_KEY_GENERATOR",

				"inputStage" : {

					"stage" : "COLLSCAN",

					"direction" : "forward"

},

		"rejectedPlans" : [ ]

},

	"serverInfo" : {

		"host" : "Chriss-MacBook-Pro.local",

		"port" : 27017,

		"version" : "4.1.10",

		"gitVersion" : "8cdc51e7810f7fd8898a4c60b935e389f04659ee"

},

	"ok" : 1

This type of index should fail validation and not be created.

Attachments

Activity

People

Assignee:: Xin Hao Zhang (Inactive)

Reporter:: Christopher Harris

Participants:: Christopher Harris, Githook User, Xin Hao Zhang

Votes:: 0 Vote for this issue

Watchers:: 6 Start watching this issue

Dates

Created:: May 21 2019 08:40:01 PM UTC

Updated:: Apr 30 2020 02:34:00 PM UTC

Resolved:: Jun 14 2019 01:48:10 PM UTC