Hi,
Our DB is on Atlas it it’s been always kept between at 10-15% CPU usage. As soon as we have one node process running Meteor 1.9.1 that has users connected to it, the CPU averages at 35-40% with peaks at 60-80% (never seen before).
I have not found any ticket or post regarding this. Has anyone else experienced this ?
We’re hesitating between rolling back to 1.6.1.
Regards,
Burni
As soon as we restarted one of our node processes, Mongo started to receive “aggregates” queries from Meteor on a collection we have never used aggregates.
So it seems the mongo driver is doing something that is translated into an aggregate ?
Since those are slow, well, the CPU spikes a lot.
Any idea ?
That looks like a count of the collection
Exactly! we’ve just found it.
The count was “ligher” in Meteor 2.6.1 . Now it seems to use the aggregate and it’s way more CPU/RAM intensive.
We had a one that was running every time a user would connect. That happened every couple of seconds and it was taking a toll on the DB.
We changed the code to something else and it seems to be fixed.
We’ll monitor for a day to make sure everything is on track!
Regards,
Burni
Same issue here, since we migrate from 2.7.3 to 2.9.1, we got a lots of slow collscan queries (same kind as burni13, queries using aggregate)
I rolled back to 2.7.3 four hours ago, and no more collscan
I think creating indexes will help
@burni13 I don’t see what kind of query on js side trigger the issue
Could you provide a concrete example of what you changed in you code please ?
it was db.Collection.find().count();
The goal of the query was only to count all documents in a (now) quite large collection.
That’s way slower than it used to be!
So we changed the code behaviour to look for something else.
Do you have such queries ?
Regards,
Burni
On what would you recommend doing an index on for a find().count() ?
Regards,
Burni
collection.find().count() has a similar performance as collection.find().fetch() wherein the db has to go through the entire cursor to count the results.
The ideal way to count is collection.countDocuments() https://www.mongodb.com/docs/manual/reference/method/db.collection.countDocuments/
I note that countDocuments() is not yet implemented in minimongo.
if you just want to read the numbers of document in a collection then you should not scan all the documents.
You can try this: https://www.mongodb.com/docs/manual/reference/method/db.collection.estimatedDocumentCount/
or you can simply store the number of documents somewhere, you will need to update it everytime you insert or remove document(s).
