[Building Sakai] Maximum number of Sakai nodes

[Kusnetz, Jeremy]

At that Sakai conference's high concurrency BoF and later TCC meetings
it was pointed out that there is probably a maximum number of Sakai
nodes running in a cluster before you start lowering performance because
of how event caching is currently pulled through the database.  Does
anyone have a good feel to what that number may be?  Obviously some load
testing is in order but I'm looking for a good starting point.

 

Also it was mentioned that there may be a maximum JVM heap size before
you start having issues with long garbage collection times even with
proper JVM tuning.  I've heard numbers in the 8GB range.

 

Basically I'm looking for what you guys feel (especially from the TCC
team) what the largest Sakai cluster would look like before you start
getting performance penalties from growing larger.

 

As shared in the BoF we currently have maxed at about 14.5K concurrent
users and are looking to grow to about 20K concurrent users by fall.
Currently we easily hit 12K concurrent users weekly.  We have 35 Sakai
application nodes with 7GB heaps running on VMs.  At the BoF it was
widely seen that this is too many nodes and we were probably hurting our
performance.  I'd like to look at turning off some of those VMs, adding
the memory gained by shutting off those VMs and adding them back to the
existing VMs and increase their heaps.  During peak times on average we
are using about 50% of the heap, although some nodes can get closer to
75% while others are less.

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