MongoCursorTimeoutException with sort on _id - php

Question

I have an Mongo collection containing ~7 millions events. To get the events that happend for an aggregate I have the following PHP code
$client = new MongoClient();
$db = $client->selectDB('db_name');
$collection = $db->selectCollection('events');
foreach($collection->find([
'headers.for' => '89d115f8-0b2f-470e-9495-2a07d9dfb942',
])->sort([
'headers.occurredOn' => 1,
'_id' => 1,
]) as $event) {
var_dump($event);
}
When I run the above PHP code I get an MongoCursorTimeoutException after 30 seconds.
But when I run the same code without a sort on _id, so:
$client = new MongoClient();
$db = $client->selectDB('db_name');
$collection = $db->selectCollection('events');
foreach($collection->find([
'headers.for' => '89d115f8-0b2f-470e-9495-2a07d9dfb942',
])->sort([
'headers.occurredOn' => 1,
]) as $event) {
var_dump($event);
}
The error does not occur and get instant results (which is one record).
So why does a MongoCursorTimeoutException occur when a sort on _id is added?
The indexes for the collection looks as follow
[
{
"v" : 1,
"key" : {
"_id" : 1
},
"name" : "_id_",
"ns" : "db.events"
},
{
"v" : 1,
"key" : {
"headers.occurredOn" : NumberLong(1),
"_id" : NumberLong(1)
},
"name" : "headers_occurredOn_1__id_1",
"ns" : "db.events"
},
{
"v" : 1,
"key" : {
"headers.for" : NumberLong(1)
},
"name" : "headers_for_1",
"ns" : "db.events"
}
]

Answer 1

Well the problem was the indexes I had.
{
"v" : 1,
"key" : {
"headers.occurredOn" : NumberLong(1),
"_id" : NumberLong(1)
},
"name" : "headers_occurredOn_1__id_1",
"ns" : "db.events"
}
After I dropped this one and added the following:
{
"v" : 1,
"key" : {
"headers.occurredOn" : NumberLong(1)
},
"name" : "headers.occurredOn_1",
"ns" : "db.events"
}
Everything went smooth