Support sending spans in batches

[mjbryant]

The Zipkin Kafka collector supports receiving batches of spans instead of single spans after openzipkin/zipkin#995. However, having a py_zipkin user implement batching solely in the transport_handler seems like it'd be too difficult on their part.

Maybe we could support having ZipkinLoggingContext take a batch_size param that defaults to something large but sane (20?), then in log_spans we could call transport_handler with a list of thrift-encoded spans as opposed to a single span at a time.

@kaisen, thoughts?

[dmitry-prokopchenkov]

@kaisen, @bplotnick What about this? AFAIK Zipkin serer can process batch spans. At least we might modify log_spans to send root span and self.log_handler.client_spans together. What do you think? I could give a try on this.

[dmitry-prokopchenkov]

@kaisen, @bplotnick Guys, your thoughts on this?

[bplotnick]

@dmitry-prokopchenkov Go for it!

You could make log_span just write to a queue and flush when it hits a configurable batch size (with a sane default). Then at the end of log_spans, you flush the queue to write the remaining spans.

[dmitry-prokopchenkov]

@bplotnick ok, thanks!

[dmitry-prokopchenkov]

@bplotnick just a reminder, this can be closed