Error on querying FIWARE Orion with orderBy custom attribute - fiware-orion

Question

I am facing the following issue while querying Orion with orderBy, asking the results to return on chronological order. My data looks like this:
{
"id": "some_unique_id",
"type": "sensor",
"someVariable": {
"type": "String",
"value": "1",
"metadata": {}
},
"datetime": {
"type": "DateTime",
"value": "2018-09-21T00:38:57.00Z",
"metadata": {}
},
"humidity": {
"type": "Float",
"value": 55.9,
"metadata": {}
},
"someMoreVariables": {
"type": "Float",
"value": 6.29,
"metadata": {}
}
My call looks like this:
http://my.ip.com:1026/v2/entities?type=sensor&offset=SOMENUMBERMINUS30&limit=30&orderBy=datetime
Unfortunately, the response is the following:
{
"error": "InternalServerError",
"description": "Error at querying MongoDB"}
Both tenant and subtenant are used in the call, while the Orion version is 1.13.0-next and tenant has been indexed inside the MongoDB. I am running Orion and MongoDB from different Docker instances in the same server.
As always, any help will be highly appreciated.
EDIT1: After fgalan's recommendation, I am adding the relative record from the log (I am sorry, I didn't do it from the beginning):
BadInput some.ip
time=2018-10-16T07:47:36.576Z | lvl=ERROR | corr=bf8461dc-d117-11e8-b0f1-0242ac110003 | trans=1539588749-153-00000013561 | from=some.ip | srv=some_tenant | subsrv=/some_subtenant | comp=Orion | op=AlarmManager.cpp[211]:dbError | msg=Raising alarm DatabaseError: nextSafe(): { $err: "Executor error: OperationFailed: Sort operation used more than the maximum 33554432 bytes of RAM. Add an index, or specify a smaller limit.", code: 17144 }
time=2018-10-16T07:47:36.576Z | lvl=ERROR | corr=bf8461dc-d117-11e8-b0f1-0242ac110003 | trans=1539588749-153-00000013561 | from=some.ip | srv=some_tenant | subsrv=/some_subtenant | comp=Orion | op=AlarmManager.cpp[235]:dbErrorReset | msg=Releasing alarm DatabaseError
From the above, it is clear that indexing is required. I have already done that according to fgalan's answer to another question I had in the past: Indexing Orion
EDIT2: Orion response after indexing:
[
{
"v" : 2,
"key" : {
"_id" : 1
},
"name" : "_id_",
"ns" : "orion.entities"
},
{
"v" : 2,
"key" : {
"location.coords" : "2dsphere"
},
"name" : "location.coords_2dsphere",
"ns" : "orion.entities",
"2dsphereIndexVersion" : 3
},
{
"v" : 2,
"key" : {
"creDate" : 1
},
"name" : "creDate_1",
"ns" : "orion.entities"
}
]

Answer 1

You have an index {creDate: 1} which is the fine if you order by entity creation date using dateCreated (or doesn't specify the orderBy parameters, as creation date is the default ordering):
GET /v2/entities
GET /v2/entities?orderBy=dateCreated
However, if you plan to order by a different attribute defined by you (as I understand datetime is) and get the OperationFailed: Sort operation used more than the maximum error, then you have to create an index for the value of such attribute. In particular you have to create this index:
{ attrs.datetime.value: 1 }
EDIT: as suggested by a comment to this answer, the command for creating the above index typically is:
db.entities.createIndex({"attrs.datetime.value": 1});
EDIT2: have a look to this section in documentation for more detail on this kind of indexes.