Some questions about the transport and trace collect

[codecodesam]

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hello, every pinpoint developer.

pinpoint agent version:latest
branch: master

question 1:
Can i choose the udp or tcp when agent communicate with pinpoint collector?
when i use udp,should i config some value which key start with profiler.statdatasender/profiler.spandatasender?
when i use tcp,should i config some value which key start with profiler.tcpdatasender?(when i choose tcp,should i choose a protocol?grpc or thrift?)

question 2:
i find the doc ,the doc show me sampling in the agent config.
when the sampling happen in client, How does the agent ensure that the span is not lost？
there is a demo. service A invoke method with http to service B.
Has there a situation that A collector the span and B decide to filter the span?
I have an idea that I don't know if it's correct, the sampling will only happen on the first span. when service B receive request and find the HEADER which has parent span, this span will be upload

Finally, thank you for taking your precious time to look at my question.
my mail is [email protected]