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  1. Core Server
  2. SERVER-23999

Query fully covered by index still reads documents

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    Details

    • Type: Bug
    • Status: Closed
    • Priority: Major - P3
    • Resolution: Duplicate
    • Affects Version/s: 3.2.6
    • Fix Version/s: None
    • Component/s: Querying
    • Labels:
      None

      Description

      I have a collection "activities2":

      Index

      {
          action: 1,
          userId: 1,
          time: 1
      }
      

      I run a query:

      Query

      db.activities2.find({
      	userId: {
      		$in: [
      							ObjectId("5373bcfef88919d05eee3149"),
      							ObjectId("537468fff88919d05eee322c"),
      							ObjectId("537f543778f03be40e598ade"),
      							ObjectId("5382f987832983fb3a5ae9d4"),
      							ObjectId("53a561b2663e61b528241bc4"),
      							ObjectId("53a80878cde71b653ed82539"),
      							ObjectId("53a8cc6511b9cc964959c365"),
      							ObjectId("53acbfb3cb9f89250d02c48a"),
      							ObjectId("53af045ebcc79931692a4aa7"),
      							ObjectId("53b494fb9809bceb3fd25c89"),
      							ObjectId("53b6eae20c4a07fe63db10b3"),
      							ObjectId("53b831b49809bceb3fd2cfab"),
      							ObjectId("53bab1e2b5067de0061a4567"),
      							ObjectId("53bb05e1386b18ce5b20d86b"),
      		]
      	},
      	action: {
      		$in: [
      							"ANSAttempt",
      							"GooglePlusAttempt",
      							"TwitterAttempt",
      							"articleLike",
      							"articleShare",
      							"fbMessengerAttempt",
      							"fbShare",
      							"follow",
      							"forumComment_add",
      							"forumPost_add",
      							"forumPost_edit",
      							"like",
      							"objectLike_forumComment",
      							"objectLike_forumPost",
      							"objectLike_userProfileImage",
      							"objectLike_userUpdatedTagline",
      							"objectShare_forumComment",
      							"objectShare_forumPost",
      							"share",
      							"signin",
      							"userUpdatedPicture",
      							"userUpdatedTagline"
      		]
      	},
      	time: {
      		"$lt" : toDate,
      //		"$gte": fromDate,
      	}
      }, {
      	action: 1,
      	userId: 1,
      	time: 1,
      	_id: 0,
      })
      .sort({
      	time: -1
      })
      .limit(100)
      .hint({
      	action: 1,
      	userId: 1,
      	time: 1,
      })
      .explain(1)
      

      Partial explain result:

      Explain

      {
          "executionSuccess" : true, 
          "nReturned" : NumberInt(100), 
          "executionTimeMillis" : NumberInt(10), 
          "totalKeysExamined" : NumberInt(2210), 
          "totalDocsExamined" : NumberInt(2210), 
          "executionStages" : {
              "stage" : "PROJECTION", 
              "nReturned" : NumberInt(100), 
              "executionTimeMillisEstimate" : NumberInt(10), 
              "works" : NumberInt(2313), 
              "advanced" : NumberInt(100), 
              "needTime" : NumberInt(2212), 
              "needYield" : NumberInt(0), 
              "saveState" : NumberInt(18), 
              "restoreState" : NumberInt(18), 
              "isEOF" : NumberInt(1), 
              "invalidates" : NumberInt(0), 
              "transformBy" : {
                  "action" : NumberInt(1), 
                  "userId" : NumberInt(1), 
                  "time" : NumberInt(1), 
                  "_id" : NumberInt(0)
              }, 
              "inputStage" : {
                  "stage" : "SORT", 
                  "nReturned" : NumberInt(100), 
                  "executionTimeMillisEstimate" : NumberInt(10), 
                  "works" : NumberInt(2313), 
                  "advanced" : NumberInt(100), 
                  "needTime" : NumberInt(2212), 
                  "needYield" : NumberInt(0), 
                  "saveState" : NumberInt(18), 
                  "restoreState" : NumberInt(18), 
                  "isEOF" : NumberInt(1), 
                  "invalidates" : NumberInt(0), 
                  "sortPattern" : {
                      "time" : NumberInt(-1)
                  }, 
                  "memUsage" : NumberInt(9432), 
                  "memLimit" : NumberInt(33554432), 
                  "limitAmount" : NumberInt(100), 
                  "inputStage" : {
                      "stage" : "SORT_KEY_GENERATOR", 
                      "nReturned" : NumberInt(0), 
                      "executionTimeMillisEstimate" : NumberInt(10), 
                      "works" : NumberInt(2212), 
                      "advanced" : NumberInt(0), 
                      "needTime" : NumberInt(1), 
                      "needYield" : NumberInt(0), 
                      "saveState" : NumberInt(18), 
                      "restoreState" : NumberInt(18), 
                      "isEOF" : NumberInt(1), 
                      "invalidates" : NumberInt(0), 
                      "inputStage" : {
                          "stage" : "FETCH", 
                          "nReturned" : NumberInt(2210), 
                          "executionTimeMillisEstimate" : NumberInt(10), 
                          "works" : NumberInt(2211), 
                          "advanced" : NumberInt(2210), 
                          "needTime" : NumberInt(0), 
                          "needYield" : NumberInt(0), 
                          "saveState" : NumberInt(18), 
                          "restoreState" : NumberInt(18), 
                          "isEOF" : NumberInt(1), 
                          "invalidates" : NumberInt(0), 
                          "docsExamined" : NumberInt(2210), 
                          "alreadyHasObj" : NumberInt(0), 
                          "inputStage" : {
                              "stage" : "IXSCAN", 
                              "nReturned" : NumberInt(2210), 
                              "executionTimeMillisEstimate" : NumberInt(10), 
                              "works" : NumberInt(2211), 
                              "advanced" : NumberInt(2210), 
                              "needTime" : NumberInt(0), 
                              "needYield" : NumberInt(0), 
                              "saveState" : NumberInt(18), 
                              "restoreState" : NumberInt(18), 
                              "isEOF" : NumberInt(1), 
                              "invalidates" : NumberInt(0), 
                              "keyPattern" : {
                                  "action" : NumberInt(1), 
                                  "userId" : NumberInt(1), 
                                  "time" : NumberInt(1)
                              }, 
                              "indexName" : "action_1_userId_1_time_1", 
                              "isMultiKey" : false, 
                              "isUnique" : false, 
                              "isSparse" : false, 
                              "isPartial" : false, 
                              "indexVersion" : NumberInt(1), 
                              "direction" : "backward", 
                              "indexBounds" : {
                                  "action" : [
                                      "[\"userUpdatedTagline\", \"userUpdatedTagline\"]", 
                                      "[\"userUpdatedPicture\", \"userUpdatedPicture\"]", 
                                      "[\"signin\", \"signin\"]", 
                                      "[\"share\", \"share\"]", 
                                      "[\"objectShare_forumPost\", \"objectShare_forumPost\"]", 
                                      "[\"objectShare_forumComment\", \"objectShare_forumComment\"]", 
                                      "[\"objectLike_userUpdatedTagline\", \"objectLike_userUpdatedTagline\"]", 
                                      "[\"objectLike_userProfileImage\", \"objectLike_userProfileImage\"]", 
                                      "[\"objectLike_forumPost\", \"objectLike_forumPost\"]", 
                                      "[\"objectLike_forumComment\", \"objectLike_forumComment\"]", 
                                      "[\"like\", \"like\"]", 
                                      "[\"forumPost_edit\", \"forumPost_edit\"]", 
                                      "[\"forumPost_add\", \"forumPost_add\"]", 
                                      "[\"forumComment_add\", \"forumComment_add\"]", 
                                      "[\"follow\", \"follow\"]", 
                                      "[\"fbShare\", \"fbShare\"]", 
                                      "[\"fbMessengerAttempt\", \"fbMessengerAttempt\"]", 
                                      "[\"articleShare\", \"articleShare\"]", 
                                      "[\"articleLike\", \"articleLike\"]", 
                                      "[\"TwitterAttempt\", \"TwitterAttempt\"]", 
                                      "[\"GooglePlusAttempt\", \"GooglePlusAttempt\"]", 
                                      "[\"ANSAttempt\", \"ANSAttempt\"]"
                                  ], 
                                  "userId" : [
                                      "[ObjectId('53bb05e1386b18ce5b20d86b'), ObjectId('53bb05e1386b18ce5b20d86b')]", 
                                      "[ObjectId('53bab1e2b5067de0061a4567'), ObjectId('53bab1e2b5067de0061a4567')]", 
                                      "[ObjectId('53b831b49809bceb3fd2cfab'), ObjectId('53b831b49809bceb3fd2cfab')]", 
                                      "[ObjectId('53b6eae20c4a07fe63db10b3'), ObjectId('53b6eae20c4a07fe63db10b3')]", 
                                      "[ObjectId('53b494fb9809bceb3fd25c89'), ObjectId('53b494fb9809bceb3fd25c89')]", 
                                      "[ObjectId('53af045ebcc79931692a4aa7'), ObjectId('53af045ebcc79931692a4aa7')]", 
                                      "[ObjectId('53acbfb3cb9f89250d02c48a'), ObjectId('53acbfb3cb9f89250d02c48a')]", 
                                      "[ObjectId('53a8cc6511b9cc964959c365'), ObjectId('53a8cc6511b9cc964959c365')]", 
                                      "[ObjectId('53a80878cde71b653ed82539'), ObjectId('53a80878cde71b653ed82539')]", 
                                      "[ObjectId('53a561b2663e61b528241bc4'), ObjectId('53a561b2663e61b528241bc4')]", 
                                      "[ObjectId('5382f987832983fb3a5ae9d4'), ObjectId('5382f987832983fb3a5ae9d4')]", 
                                      "[ObjectId('537f543778f03be40e598ade'), ObjectId('537f543778f03be40e598ade')]", 
                                      "[ObjectId('537468fff88919d05eee322c'), ObjectId('537468fff88919d05eee322c')]", 
                                      "[ObjectId('5373bcfef88919d05eee3149'), ObjectId('5373bcfef88919d05eee3149')]"
                                  ], 
                                  "time" : [
                                      "(new Date(1461292516649), true)"
                                  ]
                              }, 
                              "keysExamined" : NumberInt(2210), 
                              "dupsTested" : NumberInt(0), 
                              "dupsDropped" : NumberInt(0), 
                              "seenInvalidated" : NumberInt(0)
                          }
                      }
                  }
              }
          }, 
          "allPlansExecution" : [
          ]
      }
      

      A collection data is attached.

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                • Created:
                  Updated:
                  Resolved: