MongoDB slow with index and sort - mongodb

Question

I have compound index:
{
"hidden" : 1,
"country" : 1,
"edited" : 1,
"changeset.when" : -1
}
And query:
{
"country" : "ua",
"edited" : true,
"hidden" : false,
"changeset.when" : { "$lt" : ISODate("5138-11-16T09:46:40Z") }
}
It works well and fast. Now I want to sort result by: { "changeset.when" : -1 } and it slows down a lot. From hundred of milliseconds to 15 seconds.
And here is explain for query with sorting:
"winningPlan" : {
"stage" : "SORT",
"sortPattern" : {
"changeset.when" : -1
},
"limitAmount" : 15,
"inputStage" : {
"stage" : "SORT_KEY_GENERATOR",
"inputStage" : {
"stage" : "FETCH",
"inputStage" : {
"stage" : "IXSCAN",
"keyPattern" : {
"hidden" : 1,
"country" : 1,
"edited" : 1,
"changeset.when" : -1
},
"indexName" : "edited_news",
"isMultiKey" : true,
"multiKeyPaths" : {
"hidden" : [ ],
"country" : [ ],
"edited" : [ ],
"changeset.when" : [
"changeset"
]
},
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 2,
"direction" : "forward",
"indexBounds" : {
"hidden" : [
"[false, false]"
],
"country" : [
"[\"ua\", \"ua\"]"
],
"edited" : [
"[true, true]"
],
"changeset.when" : [
"(new Date(100000000000000), true)"
]
}
}
}
}
}
Why is it so slow? Explain shows that it successfully uses needed index and field changeset.when is in descending order.

Answer 1

In case if you have compound index try to create query key sequence like your index sequencency. It will bring more performance.
You don't need to make aditional sort for result, by default result will be sorted according index (in your case result will be sorted descending by changeset.when)
For more info please share some documents from your collection.
If you have any question feel free to ask