Limit the length for all fields

[alvarolobato]

All fields should be limited to KEYWORD_MAX_LENGTH, with the exception of the fields noted in the long fields spec, which should be limited to a length of 10000. Optionally, we can make the latter limit configurable, as stated in the spec.

[basepi]

I think this is enforced for most things at this point.

• SQL queries are shortened in the dbapi2 code.
• Local vars are shortened in the client code

Obviously any keyword fields are already shortened.

@beniwohli I think with the age of this issue I'm going to close it as resolved. If we do run into any more issues I suppose we could write a processor that would shorten everything -- but that's probably not a precise-enough instrument, since different things need to be shortened differently. Keep me posted if you think there's still work to do here.

[basepi]

Just kidding. Found some more conversation in the cross-agent meta issue, I guess this is still in flux despite the issue-open date. Pardon my noise.

[trentm]

https://github.com/elastic/apm/blob/main/specs/agents/field-limits.md#long_field_max_length-configuration was spec'd a while ago. That covers a specific set of fields. (The Node.js APM agent truncates other fields at 1024.)

[basepi]

LONG_FIELD_MAX_LENGTH introduced in #1610 and added to Django's capture_body. First of many places.

[basepi]

Length of exception message field limited in https://github.com/elastic/apm-agent-python/pull/1619

[basepi]

Length of Starlette bodies limited in https://github.com/elastic/apm-agent-python/pull/1549