I'm building a data pipeline using TPL Dataflow to migrate data from a database to an external API. As this data pipeline could run for a long time, I was looking for a good way to monitor the progress. This turned out to be a perfect use case for Event Counters.
So far we have seen how to create a simple EventCounter using a PollingCounter and how to read out its value using the dotnet-counters global tool.
The PollingCounter uses a callback to determine the value that is reported. With each time interval, the user provided callback function is invoked and the return value is used as the counter value. This allows us to manage and track the number of migrated documents ourselves.
Let’s continue today and have a look at how we can use some of the other counters to improve our metrics.
Tracking the migration rate using the IncrementingPollingCounter
We are already tracking the number of migrated documents. Wouldn’t it be nice to also track the number of documents that are migrated in a certain interval, or better said the rate at which documents are migrated.
The good news is that we don’t have to do a lot to get this working. This is a perfect use case for the IncrementingPollingCounter.
From the documentation:
The IncrementingPollingCounter uses a callback to determine the reported increment value. With each time interval, the callback is invoked, and then the difference between the current invocation, and the last invocation is the reported value.
Let’s update our code to introduce this second metric.
- We create a new variable of type
IncrementingPollingCounter: - And instantiate this variable in our constructor.
Let’s run dotnet-counters again to see the results:
dotnet-counters monitor --process-id 32072--counters Migrator.MigratedRecordsCounter
Now we get 2 values back; our Migration Count total and the Migration Rate.
Remark: In the code above you saw that I also could specify a DisplayRateTimeScale. I expected that this would allow me to set the interval at which the value should be read. However it turned out that this value is ignored and that the dotnet-counters will always use an interval of 1 second.
This is by design. More about this here.
UPDATE: I made the full example available on Github: https://github.com/wullemsb/EventCounters