covered index should be used when null inequality is in the query and index is not multikey

XMLWordPrintableJSON

    • Fully Compatible
    • ALL
    • Query 2018-05-21, Query 2018-06-04, Query 2018-06-18, Query 2018-07-02
    • 0
    • None
    • None
    • None
    • None
    • None
    • None
    • None

      Having index on

      {a:1, b:1}

      here are some plans:
      Good:

      > db.ix.explain().find({a:1,b:2},{_id:0,a:1})
{
	"queryPlanner" : {
		"plannerVersion" : 1,
		"namespace" : "test.ix",
		"indexFilterSet" : false,
		"parsedQuery" : {
			"$and" : [
				{
					"a" : {
						"$eq" : 1
					}
				},
				{
					"b" : {
						"$eq" : 2
					}
				}
			]
		},
		"winningPlan" : {
			"stage" : "PROJECTION",
			"transformBy" : {
				"_id" : 0,
				"a" : 1
			},
			"inputStage" : {
				"stage" : "IXSCAN",
				"keyPattern" : {
					"a" : 1,
					"b" : 1
				},
				"indexName" : "a_1_b_1",
				"isMultiKey" : false,
				"multiKeyPaths" : {
					"a" : [ ],
					"b" : [ ]
				},
				"isUnique" : false,
				"isSparse" : false,
				"isPartial" : false,
				"indexVersion" : 2,
				"direction" : "forward",
				"indexBounds" : {
					"a" : [
						"[1.0, 1.0]"
					],
					"b" : [
						"[2.0, 2.0]"
					]
				}
			}
		},
		"rejectedPlans" : [ ]
	},
	"serverInfo" : {
		"host" : "altoros4",
		"port" : 34001,
		"version" : "3.5.1-89-g7b68733",
		"gitVersion" : "7b68733fae7ce8d91f9a5fda67b9972c15a20ef0"
	},
	"ok" : 1
}

      Good:

      > db.ix.explain().find({a:1,b:{$ne:2}},{_id:0,a:1})
{
	"queryPlanner" : {
		"plannerVersion" : 1,
		"namespace" : "test.ix",
		"indexFilterSet" : false,
		"parsedQuery" : {
			"$and" : [
				{
					"a" : {
						"$eq" : 1
					}
				},
				{
					"$nor" : [
						{
							"b" : {
								"$eq" : 2
							}
						}
					]
				}
			]
		},
		"winningPlan" : {
			"stage" : "PROJECTION",
			"transformBy" : {
				"_id" : 0,
				"a" : 1
			},
			"inputStage" : {
				"stage" : "IXSCAN",
				"keyPattern" : {
					"a" : 1,
					"b" : 1
				},
				"indexName" : "a_1_b_1",
				"isMultiKey" : false,
				"multiKeyPaths" : {
					"a" : [ ],
					"b" : [ ]
				},
				"isUnique" : false,
				"isSparse" : false,
				"isPartial" : false,
				"indexVersion" : 2,
				"direction" : "forward",
				"indexBounds" : {
					"a" : [
						"[1.0, 1.0]"
					],
					"b" : [
						"[MinKey, 2.0)",
						"(2.0, MaxKey]"
					]
				}
			}
		},
		"rejectedPlans" : [ ]
	},
	"serverInfo" : {
		"host" : "altoros4",
		"port" : 34001,
		"version" : "3.5.1-89-g7b68733",
		"gitVersion" : "7b68733fae7ce8d91f9a5fda67b9972c15a20ef0"
	},
	"ok" : 1
}

      Bad:

      > db.ix.explain().find({a:1,b:{$ne:null}},{_id:0,a:1})
{
	"queryPlanner" : {
		"plannerVersion" : 1,
		"namespace" : "test.ix",
		"indexFilterSet" : false,
		"parsedQuery" : {
			"$and" : [
				{
					"a" : {
						"$eq" : 1
					}
				},
				{
					"$nor" : [
						{
							"b" : {
								"$eq" : null
							}
						}
					]
				}
			]
		},
		"winningPlan" : {
			"stage" : "PROJECTION",
			"transformBy" : {
				"_id" : 0,
				"a" : 1
			},
			"inputStage" : {
				"stage" : "FETCH",
				"filter" : {
					"$nor" : [
						{
							"b" : {
								"$eq" : null
							}
						}
					]
				},
				"inputStage" : {
					"stage" : "IXSCAN",
					"keyPattern" : {
						"a" : 1,
						"b" : 1
					},
					"indexName" : "a_1_b_1",
					"isMultiKey" : false,
					"multiKeyPaths" : {
						"a" : [ ],
						"b" : [ ]
					},
					"isUnique" : false,
					"isSparse" : false,
					"isPartial" : false,
					"indexVersion" : 2,
					"direction" : "forward",
					"indexBounds" : {
						"a" : [
							"[1.0, 1.0]"
						],
						"b" : [
							"[MinKey, null)",
							"(null, MaxKey]"
						]
					}
				}
			}
		},
		"rejectedPlans" : [ ]
	},
	"serverInfo" : {
		"host" : "altoros4",
		"port" : 34001,
		"version" : "3.5.1-89-g7b68733",
		"gitVersion" : "7b68733fae7ce8d91f9a5fda67b9972c15a20ef0"
	},
	"ok" : 1
}

      Why is there a FETCH to compare b!=null? Seems like a bug.

            Assignee:
            Charlie Swanson
            Reporter:
            Asya Kamsky
            Votes:
            5 Vote for this issue
            Watchers:
            15 Start watching this issue

              Created:
              Updated:
              Resolved: