On Fri, Nov 04, 2011 at 04:57:31PM +0000, Steven Whitehouse wrote: > Hi, > > On Fri, 2011-11-04 at 12:31 -0400, David Teigland wrote: > > On Fri, Nov 04, 2011 at 03:19:49PM +0000, Steven Whitehouse wrote: > > > The three pairs of mean/variance measure the following > > > things: > > > > > > 1. DLM lock time (non-blocking requests) > > > > You don't need to track and save this value, because all results will be > > one of three values which can gather once: > > > > short: the dir node and master node are local: 0 network round trip > > medium: one is local, one is remote: 1 network round trip > > long: both are remote: 2 network round trips > > > > Once you've measured values for short/med/long, then you're done. > > The distribution will depend on the usage pattern. > > > The reason for tracking this is to be able to compare it with the > blocking request value to (I hope) get a rough idea of the difference > between the two, which may indicate contention on the lock. So this > is really a "baseline" measurement. > > Plus we do need to measure it, since it will vary according to a > number of things, such as what hardware is in use.
Right, but the baseline shouldn't change once you have it. > > > 2. To spot performance issues more easily > > > > Apart from contention, I'm not sure there are many perf issues that dlm > > measurements would help with. > > > That is the #1 cause of reported performance issues, so top of our list > to work on. The goal is to make it easier to track down the source of > these kinds of problems. I still think that time averages and computations sounds like a difficult and indirect way of measuring contention... but see how it works. Dave
