Re: NUMCPUVPS settings for a four-processor server

Bill Border wrote: + We have found that in the case of systems with very fast CPU's that + there are times that you need to set NUMCPUVPS to more than the number + of physical CPU's. We have a T600 with 10 CPU's where we configure + 15 CPU VP's and we still cannot drive the all CPU's to 100% busy. When + we were using 8 or 9 CPU VP's, we had long VP ready queues and the + system was only 60% busy. Just out of curiosity, what version of Informix are you running? I ran into this same thing years ago when I worked for Informix. It was pretty much dependant on the platform - saw it all the time on HPs, almost never on Suns. Gary Kelley (father of ODS) said that they should have adjusted the alg for determining how many threads to spawn based on the target processor (i.e. an HP port should spawn more threads). Increasing the NUMCPUVPS essentially impacts that algorithm, so you get more work for the procs to do. The question begged is, does the increased cpu utilization translate to increased performance? Just context switching all those extra virtual processors is going to chew up additional cpu time; doesn't mean significantly more time is being spent on behalf of your queries, necessarily. Dave