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  1. Core Server
  2. SERVER-15208

Inefficient index bounds applied to $or query

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    • Type: Icon: Bug Bug
    • Resolution: Duplicate
    • Priority: Icon: Major - P3 Major - P3
    • None
    • Affects Version/s: 2.6.3, 2.6.4
    • Component/s: Querying
    • None
    • ALL
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      Create one or more documents with three fields: a, b, c
      Create two indexes {a:1, b:1} and {a:1, c:1}
      Attempt query on a while including an $or on b and c.

      > db.or.find()
{ "_id" : ObjectId("5410beba0bae8df4a3526ffd"), "a" : 1, "b" : 1, "c" : 3 }
> db.or.getIndexKeys()
[ { "_id" : 1 }, { "a" : 1, "b" : 1 }, { "a" : 1, "c" : 1 } ]
> db.or.find({a:1, $or:[{b:1},{c:2}]}).explain(true)
{
	"cursor" : "BtreeCursor a_1_b_1",
	"isMultiKey" : false,
	"n" : 1,
	"nscannedObjects" : 1,
	"nscanned" : 1,
	"nscannedObjectsAllPlans" : 2,
	"nscannedAllPlans" : 2,
	"scanAndOrder" : false,
	"indexOnly" : false,
	"nYields" : 0,
	"nChunkSkips" : 0,
	"millis" : 0,
	"indexBounds" : {
		"a" : [
			[
				1,
				1
			]
		],
		"b" : [
			[
				{
					"$minElement" : 1
				},
				{
					"$maxElement" : 1
				}
			]
		]
	},
	"allPlans" : [
		{
			"cursor" : "BtreeCursor a_1_b_1",
			"isMultiKey" : false,
			"n" : 1,
			"nscannedObjects" : 1,
			"nscanned" : 1,
			"scanAndOrder" : false,
			"indexOnly" : false,
			"nChunkSkips" : 0,
			"indexBounds" : {
				"a" : [
					[
						1,
						1
					]
				],
				"b" : [
					[
						{
							"$minElement" : 1
						},
						{
							"$maxElement" : 1
						}
					]
				]
			}
		},
		{
			"cursor" : "BtreeCursor a_1_c_1",
			"isMultiKey" : false,
			"n" : 1,
			"nscannedObjects" : 1,
			"nscanned" : 1,
			"scanAndOrder" : false,
			"indexOnly" : false,
			"nChunkSkips" : 0,
			"indexBounds" : {
				"a" : [
					[
						1,
						1
					]
				],
				"c" : [
					[
						{
							"$minElement" : 1
						},
						{
							"$maxElement" : 1
						}
					]
				]
			}
		}
	],
	"server" : XXX",
	"filterSet" : false,
	"stats" : {
		"type" : "KEEP_MUTATIONS",
		"works" : 3,
		"yields" : 0,
		"unyields" : 0,
		"invalidates" : 0,
		"advanced" : 1,
		"needTime" : 0,
		"needFetch" : 0,
		"isEOF" : 1,
		"children" : [
			{
				"type" : "FETCH",
				"works" : 2,
				"yields" : 0,
				"unyields" : 0,
				"invalidates" : 0,
				"advanced" : 1,
				"needTime" : 0,
				"needFetch" : 0,
				"isEOF" : 1,
				"alreadyHasObj" : 0,
				"forcedFetches" : 0,
				"matchTested" : 1,
				"children" : [
					{
						"type" : "IXSCAN",
						"works" : 1,
						"yields" : 0,
						"unyields" : 0,
						"invalidates" : 0,
						"advanced" : 1,
						"needTime" : 0,
						"needFetch" : 0,
						"isEOF" : 1,
						"keyPattern" : "{ a: 1.0, b: 1.0 }",
						"boundsVerbose" : "field #0['a']: [1.0, 1.0], field #1['b']: [MinKey, MaxKey]",
						"isMultiKey" : 0,
						"yieldMovedCursor" : 0,
						"dupsTested" : 0,
						"dupsDropped" : 0,
						"seenInvalidated" : 0,
						"matchTested" : 0,
						"keysExamined" : 1,
						"children" : [ ]
					}
				]
			}
		]
	}
}
      Show
      Create one or more documents with three fields: a, b, c Create two indexes {a:1, b:1} and {a:1, c:1} Attempt query on a while including an $or on b and c. > db.or.find() { "_id" : ObjectId( "5410beba0bae8df4a3526ffd" ), "a" : 1, "b" : 1, "c" : 3 } > db.or.getIndexKeys() [ { "_id" : 1 }, { "a" : 1, "b" : 1 }, { "a" : 1, "c" : 1 } ] > db.or.find({a:1, $or:[{b:1},{c:2}]}).explain( true ) { "cursor" : "BtreeCursor a_1_b_1" , "isMultiKey" : false , "n" : 1, "nscannedObjects" : 1, "nscanned" : 1, "nscannedObjectsAllPlans" : 2, "nscannedAllPlans" : 2, "scanAndOrder" : false , "indexOnly" : false , "nYields" : 0, "nChunkSkips" : 0, "millis" : 0, "indexBounds" : { "a" : [ [ 1, 1 ] ], "b" : [ [ { "$minElement" : 1 }, { "$maxElement" : 1 } ] ] }, "allPlans" : [ { "cursor" : "BtreeCursor a_1_b_1" , "isMultiKey" : false , "n" : 1, "nscannedObjects" : 1, "nscanned" : 1, "scanAndOrder" : false , "indexOnly" : false , "nChunkSkips" : 0, "indexBounds" : { "a" : [ [ 1, 1 ] ], "b" : [ [ { "$minElement" : 1 }, { "$maxElement" : 1 } ] ] } }, { "cursor" : "BtreeCursor a_1_c_1" , "isMultiKey" : false , "n" : 1, "nscannedObjects" : 1, "nscanned" : 1, "scanAndOrder" : false , "indexOnly" : false , "nChunkSkips" : 0, "indexBounds" : { "a" : [ [ 1, 1 ] ], "c" : [ [ { "$minElement" : 1 }, { "$maxElement" : 1 } ] ] } } ], "server" : XXX", "filterSet" : false , "stats" : { "type" : "KEEP_MUTATIONS" , "works" : 3, "yields" : 0, "unyields" : 0, "invalidates" : 0, "advanced" : 1, "needTime" : 0, "needFetch" : 0, "isEOF" : 1, "children" : [ { "type" : "FETCH" , "works" : 2, "yields" : 0, "unyields" : 0, "invalidates" : 0, "advanced" : 1, "needTime" : 0, "needFetch" : 0, "isEOF" : 1, "alreadyHasObj" : 0, "forcedFetches" : 0, "matchTested" : 1, "children" : [ { "type" : "IXSCAN" , "works" : 1, "yields" : 0, "unyields" : 0, "invalidates" : 0, "advanced" : 1, "needTime" : 0, "needFetch" : 0, "isEOF" : 1, "keyPattern" : "{ a: 1.0, b: 1.0 }" , "boundsVerbose" : "field #0[ 'a' ]: [1.0, 1.0], field #1[ 'b' ]: [MinKey, MaxKey]" , "isMultiKey" : 0, "yieldMovedCursor" : 0, "dupsTested" : 0, "dupsDropped" : 0, "seenInvalidated" : 0, "matchTested" : 0, "keysExamined" : 1, "children" : [ ] } ] } ] } }

      Previous versions of mongo seemed good about assembling index bounds that included fields external and internal to an $or clause. This does not currently appear to be the case for the relatively simple query structure:

      {a:1, $or: [

      {b:1}

      ,

      {c:1}

      ]}

            Assignee:
            Unassigned Unassigned
            Reporter:
            ericsedor Eric Sedor
            Votes:
            2 Vote for this issue
            Watchers:
            6 Start watching this issue

              Created:
              Updated:
              Resolved: