Have found some potential performance or stability issues associated
with lots of mutex blocking in getting a parent span's context. Want
the ability to totally disable tracing to help debugging.
This commit implements BSI with variable bit depth using a
sign magnitudeto indicate whether a value is positive or negative.
This also rearranges the existence bit to be the first bit instead
of the last bit.
Explained in a comment:
We default these Max File/Map counts very high. This is basically a
backwards compatibility thing where we don't want to cause different
behavior for those who had previously set their system limits high,
and weren't experiencing any bad behavior. Ideally you want these set
a bit below your system limits.
set sane defaults. The performance overhead seems to be negligible, and this will allow us to obtain mutex and blocking profiles from running Pilosas by default.
close files after using them if global max is passed.
I originally implemented this without the global count—just always closing files
when done with them, and reopening for new writes. This was crazy slow for that
one test that uses mustSetBits in a big loop. I modified the test to use
importRoaring and everything worked better (though much more slowly).
After adding the global counter, I ran the tests with that one test using
mustSetBits again, and the performance was similar to master. After completing
this PR, I ran the tests with the max limit set to 5—they still passed but were
much slower.
