Re: Anyone interested in improving postgresql scaling?

[Kevin Way]

Kris Kennaway wrote:

If so, then your task is the following:

Make SYSV semaphores less dumb about process wakeups.  Currently
whenever the semaphore state changes, all processes sleeping on the
semaphore are woken, even if we only have released enough resources
for one waiting process to claim.  i.e. there is a thundering herd
wakeup situation which destroys performance at high loads.  Fixing
this will involve replacing the wakeup() calls with appropriate
amounts of wakeup_one().

Could this cause problem cause a situation where an 8-Core system was 50-75% slower than an otherwise equivalent 2-Core system?

I have a graph of my sysbench/pgsql results here:

   http://blog.insidesystems.net/files/sysctl-pgsq-amd64-wtf.png





Kevin Way
Inside Systems, Inc.

As the graph shows, the 8-core system is about half the speed of the 2-core system at 2 simultaneous threads, and it decays down to approximately 1/4 the speed of the 2-core system as the # of threads hits 5. All other (non-pgsql, non-sysv) tests came back approximately as expected, but I'm left wondering if I did something wrong, or if 8 cpus are slower than 2, when it comes to Postgres on currently available FreeBSD. (Full detail of what I did is available at: http://blog.insidesystems.net/articles/2007/04/09/what-did-i-do-wrong )

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