add a mechanism to record db.response.status_code

[aereal]

Problem Statement

The latest semantic conventions has introduced db.response.status_code attribute that is the status code returned by the database.

Usually it represents an error code, but may also represent partial success, warning, or differentiate between various types of successful outcomes.

The latest otelsql provides AttributesGetter but it is called only when creating a span:

otelsql/utils.go

Line 101 in c335821

attrs = append(attrs, cfg.AttributesGetter(ctx, method, query, args)...)

The recordSpanError internal function just calls RecordError and has no mechanism to extract some information from err.

So the library users can't extract the information from the error returned by the driver.

Proposed Solution

Add a new option like type ErrorEventAttributesGetter func(err error) []attribute.KeyValue and recordSpanError uses ErrorEventAttributesGetter's return values.

The users can pass the function that extracts the status information from the driver's concrete error type such as mysql.MySQLError.Number.

Alternatives

Add a new argument err error to AttributeGetter.

It is unreasonable because it breaks backward compatibilities.

Prior Art

No prior arts found.

Additional Context

[XSAM]

@aereal Thanks for raising this issue!

This is a good suggestion. I am considering creating an option to get attributes at the end of the operation for both traces and metrics. Something like type AttributeGetterOnEnd func(string signal, err error) []attribute.KeyValue. signal could be metric or trace. What do you think?

Please also notice that the db.response.status_code attribute is an experimental attribute. This attribute might be changed in the future.