James Mansion <james@xxxxxxxxxxxxxxxxxxxxxx> wrote: > Kevin Grittner wrote: >> Sure, but the architecture of those products is based around all >> the work being done by "engines" which try to establish affinity to >> different CPUs, and loop through the various tasks to be done. You >> don't get a context switch storm because you normally have the >> number of engines set at or below the number of CPUs. The down >> side is that they spend a lot of time spinning around queue access >> to see if anything has become available to do -- which causes them >> not to play nice with other processes on the same box. >> > This is just misleading at best. What part? Last I checked, Sybase ASE and SQL Server worked as I described. Those are the products I was describing. Or is it misleading to say that you aren't likely to get a context switch storm if you keep your active thread count at or below the number of CPUs? > I'm sorry, but (in particular) UNIX systems have routinely > managed large numbers of runnable processes where the run queue > lengths are long without such an issue. Well, the OP is looking at tens of thousands of connections. If we have a process per connection, how many tens of thousands can we handle before we get into problems with exhausting possible pid numbers (if nothing else)? > This is not an issue with the number of runnable threads, > but with the way that they wait and what they do. Well, I rather think it's about both. From a description earlier in this thread, it sounds like Oracle effective builds a connection pool into their product, which gets used by default. The above-referenced products use a more extreme method of limiting active threads. Perhaps they're silly to do so; perhaps not. I know that if you do use a large number of threads, you have to be pretty adaptive. In our Java app that pulls data from 72 sources and replicates it to eight, plus feeding it to filters which determine what publishers for interfaces might be interested, the Sun JVM does very poorly, but the IBM JVM handles it nicely. It seems they use very different techniques for the monitors on objects which synchronize the activity of the threads, and the IBM technique does well when no one monitor is dealing with a very large number of blocking threads. They got complaints from people who had thousands of threads blocking on one monitor, so they now keep a count and switch techniques for an individual monitor if the count gets too high. Perhaps something like that (or some other new approach) might mitigate the effects of tens of thousands of processes competing for for a few resources, but it fundamentally seems unwise to turn those loose to compete if requests can be queued in some way. -Kevin -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
