census-ecosystem
Remove interface for exporting ViewData
Can we install the metrics exporter instead of the viewdata for the users, so we keep the public API?
At least I would like to avoid duplicate code to translate from viewdata to SD metrics and metrics data to Sd
The major problem is for now lots of users still do
view.RegisterExporter(stackdriverExporter)
That requires Stackdriver exporter to implement the interface ExportView(viewData *Data) (https://godoc.org/go.opencensus.io/stats/view#Exporter). If we just remove this interface from Stackdriver exporter, the above code will break. We can translate View.Data to Metric under the hood though I don't see that simplifies things a lot (still need to add the mapping from View.Data to Metric).
The mapping is already implemented in the opencensus we can re-use that.
We have a mapping from the internal representation of ViewData (called viewInternal) to Metric: https://github.com/census-instrumentation/opencensus-go/blob/29aa3cabbf25be9f1c3c6d78cecfbe0c3e20cf5a/stats/view/view_to_metric.go#L128-L149. (This method and viewInternal are not exposed btw). However we don't currently have a method to directly convert ViewData to Metric that we can reuse here.
In addition I think the performance of ExportView will get worse if we do that, because it added an extra intermediate step (ViewData -> SDMetric vs. ViewData -> Metric -> SDMetric).
Oh my...
I've spent more than a week to investigate why we have an excessive export issue in our code base and I just realized we called both view.RegisterExporter(stackdriverExporter) and exporter.StartMetricsExporter() somehow.
If we can't remove the view.Exporter interface, can we at least add a warning log when both view.RegisterExporter and exporter.StartMetricsExporter are used?
And FWIW, the official guide on writing a metric exporter still uses view.Exporter interface: https://opencensus.io/exporters/custom-exporter/go/metrics/