Manfred,
> What did you test exactly and could you explain a bit about the context
> switch storm?
PostgreSQL currently causes a CS storm (context switches > 100,000) on
multi-processor machines where you have a number of concurrent processes ( >
than the number of processors) accessing the same small quantity of data
repeatedly, particularly if doing seq scans and/or bad queries. This issue
causes a significant drop in server performance, as much as 60%.
> Did you use the futex interface directly or pthread_rwlock_rdlock?
I'll have to admit to having only a beginner's grasp of this stuff, but I do
believe that that was what the OSDL patch did. Jan also tried a simpler
patch, which didn't work either. Both Jan and Tom have expressed the
opinion that the only solution is to make the BufrMgrLock more granular (as
in, not monolithic) but this is a huge task.
--
Josh Berkus
Aglio Database Solutions
San Francisco