Azure cosmos throwing error for $round in MongoDB query pipeline - mongodb

Question

I am using Azure Cosmos MongoDB and storing API Request logs. I wanted to know how many request were made per second. So I am grouping them on basis of timestamp after dividing the timestamp by 1000 then rounding off with 0 decimal places
1593096483234 to 1593096483.234 to 1593096483
and taking count of documents furnished by above grouping then sorting on basis of count in decreasing order.
Query
db.server_api_logs.aggregate([
{
"$group": {
"_id": "$timestamp"
}
},
{
"$project": {
"summation": {
"$round": {
"$toDouble": {
"$divide": ["$_id",1000]
}
}
}
}
},
{
"$group": {
"_id": "$summation",
"summer": {"$sum": 1}
}
},
{
"$sort": {"summer": -1}
}
]
Getting this error when try to run above query
Unable to execute the selected commands
Mongo Server error (MongoCommandException): Command failed with error 168 (168): 'unknown operator: $round' on server <server address>
The full response is:
{
"ok" : 0.0,
"errmsg" : "unknown operator: $round",
"code" : NumberInt(168),
"codeName" : "168"
}
It is working totally fine on local using compass but not on Cosmos using Robo3T. Am I doing something wrong?

Answer 1

As stated in MongoDB documentation, $round operator was introduced in version 4.2 of MongoDB.
As stated in Azure Cosmos DB documentation, for this moment, Azure Cosmos DB's API for MongoDB is compatible with MongoDB server version 3.6.
This is the reason, why your query works on local MongoDB instance (I believe 4.2 or newer) but fails for Azure Cosmos DB.