first implementation of span name filters

[K-Jo]

When the path contains UUID, or Long values, the list of span names explode, In production we see that cassandra is struggling when a huge amount of different span names needs to be inserted into the database.
I created the possibility to add a filter to the span name creation. For the spring rest-easy you can add them by simply creating a config class in your project. Jersey implementation currently takes no filter. Two filters are implemented: No filter and Filter out numeric values which filters path/ab1234/path into path//path. Of course a custom filter for your application can be made.

[kristofa]

I knew from the start that simply retrieving the path from the URI and use that as span name would not work when wanting to do aggregation because we would not be able to see that /service/a/1 and /service/b/2 are requests to same service. I didn't expect it would cause issues at datastore level but I can see the issue! So thanks for taking this up!

However I see 1 issue with the implementation:

• When we change the span name on the client side we should make sure the same span name is used at the receiving end (server side). I have already foreseen a header for this X-B3-SpanName which is submitted when you call the ClientRequestHeaders#addTracingHeaders method which takes the spanName as last argument. So if your filter adapts the span name you should submit it by using the right call to ClientRequestHeaders#addTracingHeaders. Interpretation of the header is implemented at server side already.

As a side note, defining service name and span name feels like more complicated as it should :) I'll try to get my head around it one day when rainy and/or cold :) to see if we can't make it easier.

[K-Jo]

Hey Kristof,

I updated the code so it indeed adds the span name to the request headers and added tests. I took the liberty to remove the method in ClientRequestHeaders which didn't add the span name. The method wasn't used anymore except for testing, which I adapted.

Pieter

[kristofa]

Ok, will merge. Thanks.

[kristofa]

This pull request made it into brave version 2.3 which should appear in Maven Central shortly.