I have code that makes a fairly simple request-skip-limit-sort. I encounter phenomena that are difficult for me to explain.
In the "small" value of the pass - everything is in order. In the "high" skip value (> 18000) - I can not get a result with a limit above 20 without receiving the following error:
OperationFailure: Executor error during find command: OperationFailed: Sort operation used more than the maximum 33554432 bytes of RAM. Add an index, or specify a smaller limit.
The question is, why does this happen only with a large count of passes? How can i solve this?
Works on mongoShell (even with DBQuery.shellBatchSize = 300). And it looks like it uses the db.my_collection.find index ({'foo': false}). skip (19000) .limit (100) .sort ({'meta_data.created_at': - 1}). explain ()
"queryPlanner" : {
"plannerVersion" : 1,
"namespace" : "bla.my_collection",
"indexFilterSet" : false,
"parsedQuery" : {
"foo" : {
"$eq" : false
}
},
"winningPlan" : {
"stage" : "LIMIT",
"limitAmount" : 100,
"inputStage" : {
"stage" : "SKIP",
"skipAmount" : 9000,
"inputStage" : {
"stage" : "FETCH",
"inputStage" : {
"stage" : "IXSCAN",
"keyPattern" : {
"foo" : 1,
"meta_data.created_at" : -1
},
"indexName" : "foo_1_meta_data.created_at_-1",
"isMultiKey" : false,
"multiKeyPaths" : {
"foo" : [ ],
"meta_data.created_at" : [ ]
},
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 1,
"direction" : "forward",
"indexBounds" : {
"foo" : [
"[false, false]"
],
"meta_data.created_at" : [
"[MaxKey, MinKey]"
]
}
}
}
}
},
}
:
, - .
, ?
"rejectedPlans" : [
{
"stage" : "SKIP",
"skipAmount" : 19000,
"inputStage" : {
"stage" : "SORT",
"sortPattern" : {
"meta_data.created_at" : -1
},
"limitAmount" : 19100,
"inputStage" : {
"stage" : "SORT_KEY_GENERATOR",
"inputStage" : {
"stage" : "FETCH",
"inputStage" : {
"stage" : "IXSCAN",
"keyPattern" : {
"foo" : 1,
"_id" : 1
},
"indexName" : "foo_1__id_1",
"isMultiKey" : false,
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 1,
"direction" : "forward",
"indexBounds" : {
"foo" : [
"[false, false]"
],
"_id" : [
"[MinKey, MaxKey]"
]
}
}
}
}
}
}
. ? ?