OPTIMIZE: Change ServerBaseContext

[cyx]

Upon transitioning our production services to ServerBaseContext, we saw a serious regression with performance. It wasn't obvious, but I was able to narrow it down to a mysterious solution. Here's a gist of a reproducible benchmark:

https://gist.github.com/cyx/8730ab8d31996711110d9979d1715f98

Long story short, it seems if we create a copy of the base context, then we don't see this performance regression.

I'm open to discuss this some more -- and I've already picked the brains of other Go programmers in our company to see what they think. Logic dictates the copy doesn't do anything, but empirical data shows it does.

Thought this will be useful for others.

[pkieltyka]

This is very helpful thank you @cyx cc: check this out @VojtechVitek

[VojtechVitek]

Very nice catch! LGTM

Seems like the lines 118 and 121 store more and more data into baseCtx on each run, since it was a local variable in the parent function scope.

[VojtechVitek]

btw: Same pattern is used in the Throttler middleware (see https://github.com/pressly/chi/blob/master/middleware/throttler.go#L36)

I just wrote a simple use case, explaining the behavior, if you're interested: https://play.golang.org/p/wQXiuUgUKI

[cyx]

Perfect thanks for the quick turnaround. I'll get this pulled into our latest release and use it in our prod servers this week.