add an option to enable grpc tracing

[demmer]

GRPC has an option to enable tracing using the builtin golang net tracing package:
https://godoc.org/golang.org/x/net/trace

Add a flag to enable tracing the first time a grpc client or server is created.

[bbeaudreault]

I thought it was enabled by default. Did you try hitting the endpoints? They work for us with no configuration.

[bbeaudreault]

Actually, i see this was disabled by default 4 months ago. grpc/grpc-go@3214f76

cc @hmcgonig

[sougou]

I feel like this should always be enabled, but not sure what the overhead is. Should we default the flag to true instead? Thoughts?

[demmer]

I haven't measured the overhead either. However upstream changed it from default true to default false _presumably_ for a reason, so it seemed best to me that vitess would mirror that decision.

…

On Wed, Jan 3, 2018 at 1:53 PM, Sugu Sougoumarane ***@***.***> wrote: I feel like this should always be enabled, but not sure what the overhead is. Should we default the flag to true instead? Thoughts? — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <#3519 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/ADJ72OORHr03w8_9Ezwt0qVt0H5tinYnks5tG_bxgaJpZM4RRA51> .

[sougou]

LGTM
According to this, there's a price to pay: grpc/grpc-go#695. It looks like they might have fixed that particular cost separately, but let's play it safe.