Remove opencensus_task label [was: High cardinality of opencensus_task label]

[census-ecosystem]

Remove opencensus_task label [was: High cardinality of opencensus_task label]

[songy23]

Background:

We added this task label before, since it's possible that MonitoredResource alone cannot uniquely identify Stackdriver TimeSeries (e.g multiple processes running on one GCE instance), and this could cause errors:
Points must be written in order. One or more of the points specified was older than the most recent stored point.: timeSeries[0-2]

There's one section in README that also explained this.

Back to the questions:

Is there a way we can avoid this?

Currently the task label will be added to Stackdriver stats exporter in C++, Java and Go by default, and we don't have an option to disable it yet.

Does exporting deltas instead of cumulative help?

Unfortunately Stackdriver doesn't allow custom metrics to be of type Delta.

Or if we know for sure that the monitored resource is unique, can we provide an option to disable setting this label?

This could be an option. The task label is not necessary if MonitoredResource can uniquely identify the exported stats. We can let the user choose whether they want this label or not.

Since Stackdriver has extended the definition of MonitoredResourceMetadata recently, another option is to have the task label as an optional MonitoredResourceMetadata.userLabel.

[semistrict]

Plan of record is to replace the opencensus_task label with userLabels in the default MonitoredResourceMetadata, and users will also be able to override the default MonitoredResourceMetadata with Options.Resource.

[songy23]

Please note that this is a breaking change, since we're modifying the definition of previous metrics (there's one less label in the metrics). Users of Stackdriver exporter may need to delete the previous metric definitions to avoid errors.