In 6.x. the default thread library is quite inefficient although it
can make use of multiple CPUs (again, providing the application is
giving them work to do). For multi-threaded performance you will
be better off switching to the libthr library (see libmap.conf(5))
or updating to 7.0 (where it is the default). This isn't likely to
be the underlying issue if you are trying to debug a loss of
performance relative to the same configuration in the past though.
Indeed Plone is written in python, and python has a "Big Giant Lock"
inside which insures that only one thread can execute, in order to
protect the python structures. This lock is only released under special
circumstances, such as doing IO. Hence it is necessary to run several
instances of python programs and do synchronization work, if one wants
to make use of several CPUs, or use python threads, and immediately
make some IOs, or similar techniques. It may be that using Jython, if
possible, yields better threading behavior. When doing some work
according to these ideas, i had found quite severe contention, and this
was not cured when switching native threading libraries (libksd, libthr,
etc.). The problem is really inside python.
Yep, it could be that -- what confuses me though is that it is claimed
that performance suddenly regressed. If so then this cannot be the
underlying cause.
It's actually been a long, slow, steady degradation of performance as
best I can tell, that's recently just reached proportions that are so
ridiculous that it's gone from "this sucks but I can deal" to "this is
completely unusable." The system has been slow from the start, just not
this slow. I guess I'll need to investigate this...and while I know
that Python is somewhat off-topic, if anyone here has any suggestions
on where to start, they'd be much appreciated. :-)
Alex
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