Description
The example below shows a query that returns "n" larger than the size of the collection.
Set up:
> for(i=0;i<10000;i++){db.foo.insert({a:1,b:1,c:1})} |
Issue a long-running series of updates:
> for(i=0;;i++){eval("db.foo.update({},{$set:{f"+i+":true}},false,true)");} |
Meanwhile, run the following query (and note that itcount() will return values greater than 10000, the number of documents in the collection):
> db.foo.find({$or:[{a:1}, {b:1}]}).sort({c:1}).itcount()
|
7979
|
> db.foo.find({$or:[{a:1}, {b:1}]}).sort({c:1}).itcount()
|
10000
|
> db.foo.find({$or:[{a:1}, {b:1}]}).sort({c:1}).itcount()
|
11038
|
Full explain:
> db.foo.find({$or:[{a:1}, {b:1}]}).sort({c:1}).explain(true)
|
{
|
"clauses" : [
|
{
|
"cursor" : "BtreeCursor a_1_c_1",
|
"isMultiKey" : false,
|
"n" : 11126,
|
"nscannedObjects" : 0,
|
"nscanned" : 11126,
|
"scanAndOrder" : false,
|
"indexOnly" : false,
|
"nChunkSkips" : 0,
|
"indexBounds" : {
|
"a" : [
|
[
|
1,
|
1
|
]
|
],
|
"c" : [
|
[
|
{
|
"$minElement" : 1
|
},
|
{
|
"$maxElement" : 1
|
}
|
]
|
]
|
}
|
},
|
{
|
"cursor" : "BtreeCursor b_1_c_1",
|
"isMultiKey" : false,
|
"n" : 11126,
|
"nscannedObjects" : 0,
|
"nscanned" : 11126,
|
"scanAndOrder" : false,
|
"indexOnly" : false,
|
"nChunkSkips" : 0,
|
"indexBounds" : {
|
"b" : [
|
[
|
1,
|
1
|
]
|
],
|
"c" : [
|
[
|
{
|
"$minElement" : 1
|
},
|
{
|
"$maxElement" : 1
|
}
|
]
|
]
|
}
|
}
|
],
|
"cursor" : "QueryOptimizerCursor",
|
"n" : 11126,
|
"nscannedObjects" : 0,
|
"nscanned" : 22252,
|
"nscannedObjectsAllPlans" : 0,
|
"nscannedAllPlans" : 22252,
|
"scanAndOrder" : false,
|
"nYields" : 267,
|
"nChunkSkips" : 0,
|
"millis" : 2559,
|
"allPlans" : [
|
{
|
"clauses" : [
|
{
|
"cursor" : "BtreeCursor a_1_c_1",
|
"isMultiKey" : false,
|
"n" : 11126,
|
"nscannedObjects" : 0,
|
"nscanned" : 11126,
|
"scanAndOrder" : false,
|
"indexOnly" : false,
|
"nChunkSkips" : 0,
|
"indexBounds" : {
|
"a" : [
|
[
|
1,
|
1
|
]
|
],
|
"c" : [
|
[
|
{
|
"$minElement" : 1
|
},
|
{
|
"$maxElement" : 1
|
}
|
]
|
]
|
}
|
},
|
{
|
"cursor" : "BtreeCursor b_1_c_1",
|
"isMultiKey" : false,
|
"n" : 11126,
|
"nscannedObjects" : 0,
|
"nscanned" : 11126,
|
"scanAndOrder" : false,
|
"indexOnly" : false,
|
"nChunkSkips" : 0,
|
"indexBounds" : {
|
"b" : [
|
[
|
1,
|
1
|
]
|
],
|
"c" : [
|
[
|
{
|
"$minElement" : 1
|
},
|
{
|
"$maxElement" : 1
|
}
|
]
|
]
|
}
|
}
|
],
|
"cursor" : "QueryOptimizerCursor",
|
"n" : 11126,
|
"nscannedObjects" : 0,
|
"nscanned" : 22252,
|
"scanAndOrder" : false,
|
"nChunkSkips" : 0
|
}
|
],
|
"server" : "Rassi-MacBook-Pro.local:27017",
|
"filterSet" : false,
|
"stats" : {
|
"type" : "FETCH",
|
"works" : 33394,
|
"yields" : 267,
|
"unyields" : 267,
|
"invalidates" : 3365,
|
"advanced" : 11126,
|
"needTime" : 22254,
|
"needFetch" : 13,
|
"isEOF" : 1,
|
"alreadyHasObj" : 0,
|
"forcedFetches" : 0,
|
"matchTested" : 0,
|
"children" : [
|
{
|
"type" : "SORT_MERGE",
|
"works" : 33380,
|
"yields" : 267,
|
"unyields" : 267,
|
"invalidates" : 3365,
|
"advanced" : 11126,
|
"needTime" : 22254,
|
"needFetch" : 0,
|
"isEOF" : 1,
|
"dupsTested" : 22252,
|
"dupsDropped" : 11126,
|
"forcedFetches" : 0,
|
"children" : [
|
{
|
"type" : "IXSCAN",
|
"works" : 11127,
|
"yields" : 267,
|
"unyields" : 267,
|
"invalidates" : 3365,
|
"advanced" : 11126,
|
"needTime" : 0,
|
"needFetch" : 0,
|
"isEOF" : 1,
|
"keyPattern" : "{ a: 1.0, c: 1.0 }",
|
"boundsVerbose" : "field #0['a']: [1.0, 1.0], field #1['c']: [MinKey, MaxKey]",
|
"isMultiKey" : 0,
|
"yieldMovedCursor" : 0,
|
"dupsTested" : 0,
|
"dupsDropped" : 0,
|
"seenInvalidated" : 0,
|
"matchTested" : 0,
|
"keysExamined" : 11126,
|
"children" : [ ]
|
},
|
{
|
"type" : "IXSCAN",
|
"works" : 11127,
|
"yields" : 267,
|
"unyields" : 267,
|
"invalidates" : 3365,
|
"advanced" : 11126,
|
"needTime" : 0,
|
"needFetch" : 0,
|
"isEOF" : 1,
|
"keyPattern" : "{ b: 1.0, c: 1.0 }",
|
"boundsVerbose" : "field #0['b']: [1.0, 1.0], field #1['c']: [MinKey, MaxKey]",
|
"isMultiKey" : 0,
|
"yieldMovedCursor" : 0,
|
"dupsTested" : 0,
|
"dupsDropped" : 0,
|
"seenInvalidated" : 0,
|
"matchTested" : 0,
|
"keysExamined" : 11126,
|
"children" : [ ]
|
}
|
]
|
}
|
]
|
}
|
}
|