MongoDB Collection overview - missing data

Percona Monitoring and Management (PMM) PMM 3.x
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Edit: I managed to fix it. For anyone dealing with a similar problem, the issue was that the default max-collections-limit is set to 200, but since my instance had over 300 collections in total, it wasn’t getting collected at all. I simply removed the service and added it again with the flag --max-collections-limit=400 and I started to see the data.

Hi,

I’m currently using PMM to monitor multiple MongoDB instances in a replica set and I’ve run into an issue where one specific instance does not show any data in the Collection Overview dashboard.

I have 4 instances in a three node replica set (4x primaries on ServerA, 4x replicas on ServerB and 4x replicas on serverC).

All instances have been added using pmm-admin add mongodb with identical parameters (except for the unique values) - the same pmm user is created in the admin database in each instance with the same roles, the enable all collectors option is also specified.

sudo pmm-admin add mongodb --username pmm --password --environment=PROD --replication-set=<rs_name> --enable-all-collectors --service-name=<service_name> --host --port --tls

PMM agents and exporters are running for all instances as verified by pmm-admin list.

My problem is that for 3 instances, the collection metrics are visible and working as expected, but for one, the dashboard shows “No Data”. Every other dashboard successfully collects the data for all 4 instances.

The database dropdown for this one instance is also empty.

Running db.runCommand({ collStats: “” }) manually works.

The instance contains 18 databases in total, with sizes ranging from tens of MiB to tens of GiB, the largest one being 95GiB. The other instances are generally in the hundreds of MiB range and work fine, could that perhaps be the issue?

Thanks for any help in this matter!

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I don’t think the size of the database would lead to pmm-agent’s inability to scrape data from it.

One point to double check though would be whether pmm-agent has proper permissions to that database instance.

Otherwise, what do you see on PMM Inventory / Services tab? Are all instances reporting their Status “Up” and Monitoring “OK”?

If nothing helps, you may want to search for clues in the agent logs. It can’t be that a service is added but no metrics come in, there must be a reason.