Ruby 1.9 GarbageCollector, GC.disable/enable

Question

I'm developing a Rails 2.3, Ruby 1.9.1 webapplication that does quite a bunch of calculation before each request. For every request it has to calculate a graph with 300 nodes and ~1000 edges. The graph and all its nodes, edges and other objects are initialized for every request (~2000 objects) - actually they are cloned from an uncalculated cached graph using Marshal.load(Marshal.dump()).

Performance is quite an issue here. Right now the whole request takes in average 150ms. I then saw that during a request, parts of the calculation randomly take longer. Assuming, that this might be the GarbageCollector kicking in, I wrapped the request in GC.disable and GC.enable, so that the request waits with garbagecollecting until calculating and rendering have finished.

def query
  GC.disable
  calculate
  respond_to do |format| format.html {render} end
  GC.enable
end

The average request now takes about 100ms (50 ms less).

But I'm unsure if this is a good/stable solution, I assume there must be drawbacks doing that. Does anybody has experience with a similar problem or sees problems with the above code?

Answer 1

No real disadvantages, except that when re-enabled the GC will take longer to run.

There are a number of articles on the web on the tuning Ruby's GC. Take a look at them, and maybe you can remove those lines. =)

There's no way you can cache the results and redo the calcs on the background every few minutes?

Answer 2

It might looks stupid but in this case, I'll try to call a C function from your ROR. This solution is quite hardcore but it should give amazing performance results ;)

Your solution with ruby is not a long therm solution it's just a fix ...

Answer 3

If it makes your app faster, then use it.

I would add an insure statement so that if any exception is raised you don't end up with disabled garbage collection.

def query
  GC.disable
  calculate
  respond_to do |format| format.html {render} end
ensure
  GC.enable
end