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Some index accesses update the global index counters; some don't.
MongoDB shell version: 2.2.4
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connecting to: test
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> db.version()
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2.2.4
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> db.hostInfo().os
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{ "type" : "Linux", "name" : "Ubuntu", "version" : "12.04" }
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> show dbs
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local (empty)
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> db.test.insert({a:1})
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> db.test.ensureIndex({a:1})
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> db.serverStatus().indexCounters.btree
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{
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"accesses" : 1,
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"hits" : 1,
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"misses" : 0,
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"resets" : 0,
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"missRatio" : 0
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}
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> db.test.find()
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{ "_id" : ObjectId("51632bd680036fc7eb0cbdea"), "a" : 1 }
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> db.test.find({_id: ObjectId("51632bd680036fc7eb0cbdea")})
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{ "_id" : ObjectId("51632bd680036fc7eb0cbdea"), "a" : 1 }
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> db.serverStatus().indexCounters.btree
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{
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"accesses" : 2,
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"hits" : 2,
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"misses" : 0,
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"resets" : 0,
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"missRatio" : 0
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}
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> db.test.find({a:1})
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{ "_id" : ObjectId("51632bd680036fc7eb0cbdea"), "a" : 1 }
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> db.test.find({a:1}).explain()
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{
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"cursor" : "BtreeCursor a_1",
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"isMultiKey" : false,
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"n" : 1,
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"nscannedObjects" : 1,
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"nscanned" : 1,
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"nscannedObjectsAllPlans" : 1,
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"nscannedAllPlans" : 1,
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"scanAndOrder" : false,
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"indexOnly" : false,
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"nYields" : 0,
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"nChunkSkips" : 0,
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"millis" : 0,
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"indexBounds" : {
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"a" : [
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[
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1,
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1
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]
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]
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},
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"server" : "tad-ubuntu:27017"
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}
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> db.serverStatus().indexCounters.btree
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{
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"accesses" : 2,
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"hits" : 2,
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"misses" : 0,
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"resets" : 0,
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"missRatio" : 0
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}
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MongoDB shell version: 2.4.1
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connecting to: test
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> db.version()
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2.4.1
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> db.hostInfo().os
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{ "type" : "Linux", "name" : "Ubuntu", "version" : "12.04" }
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> show dbs
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local 0.078125GB
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> db.test.insert({a:1})
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> db.test.ensureIndex({a:1})
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> db.serverStatus().indexCounters
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{
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"accesses" : 1,
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"hits" : 1,
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"misses" : 0,
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"resets" : 0,
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"missRatio" : 0
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}
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> db.test.find()
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{ "_id" : ObjectId("51632d682b2597dfbeae7f92"), "a" : 1 }
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> db.test.find({_id: ObjectId("51632d682b2597dfbeae7f92")})
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{ "_id" : ObjectId("51632d682b2597dfbeae7f92"), "a" : 1 }
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> db.serverStatus().indexCounters
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{
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"accesses" : 2,
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"hits" : 2,
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"misses" : 0,
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"resets" : 0,
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"missRatio" : 0
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}
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> db.test.find({a:1})
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{ "_id" : ObjectId("51632d682b2597dfbeae7f92"), "a" : 1 }
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> db.test.find({a:1}).explain()
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{
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"cursor" : "BtreeCursor a_1",
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"isMultiKey" : false,
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"n" : 1,
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"nscannedObjects" : 1,
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"nscanned" : 1,
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"nscannedObjectsAllPlans" : 1,
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"nscannedAllPlans" : 1,
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"scanAndOrder" : false,
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"indexOnly" : false,
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"nYields" : 0,
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"nChunkSkips" : 0,
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"millis" : 0,
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"indexBounds" : {
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"a" : [
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[
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1,
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1
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]
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]
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},
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"server" : "tad-ubuntu:27017"
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}
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> db.serverStatus().indexCounters
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{
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"accesses" : 2,
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"hits" : 2,
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"misses" : 0,
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"resets" : 0,
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"missRatio" : 0
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}
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Indexed access using _id adds to the index counters. Indexed access using the "a" key in this example does not add to the index counters.
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