Comments on: PMM 101: Troubleshooting MongoDB with Percona Monitoring and Management

By: Kay Agahd

Kay Agahd — Fri, 23 Oct 2020 19:06:46 +0000

In reply to Mike Grayson. Thanks Mike! However, you still wrote "the example above could have been sent by running “use mpg; db.testData.find({“x”: { “$lte”: …, “$gt”: … }).skip(0)” while your screenshot shows an equality query. :)

By: Mike Grayson

Mike Grayson — Mon, 19 Oct 2020 19:33:44 +0000

Kay,

1) You’re correct, it was an equality condition, not a range, I changed my screenshot example and neglected to update my query, good catch :). It should be db.testData.find({“x”: “97544”)
2) PMM can store slow operations for 8 days by default, it’s configurable though and can be longer if necessary:
https://www.percona.com/doc/percona-monitoring-and-management/faq.html#how-to-control-data-retention-for-pmm
I’ll take a look at the project you shared, thank you very much for sharing!

By: Kay Agahd

Kay Agahd — Mon, 19 Oct 2020 18:20:24 +0000

Hi Mike, thanks for the intro! I have two questions though:
1) You wrote: “the example above could have been sent by running “db.testData.find({“x”: { “$lte”: …, “$gt”: … })” My question is why you think a range query was executed – I rather think it was an equality condition where x=987544 (at least this what your screenshot shows).
2) How long PMM stores the slow operations? Are they stored only in the capped collection system.profile which size is per default only 1 MB? However, this would mean that PMM could show only the very latest slow operations. How is this implemented in PMM?

You may be interested in the following open sourced project:
https://github.com/idealo/mongodb-slow-operations-profiler

It collects slow operations from one or multiple mongoDB system(s) in order to visualize and analyze them. It might inspire you or your team to add some of its functionality to PMM. That would be great!