[pcp] PCP developers meeting notes

[Nathan Scott]

----- Original Message -----
> Can I get some more info with regards to the issues with Parfait? What
> are the scalability/critical issues that were seen?

There were a few.  The first class was self-inflicted (and IIRC inherited
from Parfaits precursor) - the use of a single writeout queue with single
lock - it was always intended (and the C API implements this) that each
metric/value is written independently of any others (within the mmapped
file).

The second class of problem surrounds scaling issues within the JVM - in
particular, there is use of the ThreadLock mutex around calls from one
thread accessing threadInfo structure for another thread (problem doesn't
exist for a thread accessing its own threadInfo, that has a fast path with
no lock).  Once many threads are doing this, inter-thread contention bites
badly and the application can no longer scale to even modest numbers of
CPUs.

So, avoid those sorts of things, please.  :)

cheers.

-- 
Nathan