Thanks for the tips. I was considering trying testing again with more partitions w/ smaller machines. Perhaps N x m1.xlarge w/ 8 GB heap space.
I was starting to think that since the heap space was so big perhaps I should be worrying about page sizes as well. While I tried various GC settings (UseConcMarkSweepGC, ConcGCThreads, UseG1GC, etc. ) I didn't take a stab at playing with the size of New Genearation. Could you explain the reasoning behind this? Is the idea that most objects die young so try to increase the number of short run minor GCs and avoid bigger Major GCs? I am quite interested.
Edit: Regarding the cluster you were working on. Would you be able to give general dimensions to the number of nodes & partitions in your cluster + memory for each? Just trying to get a general guideline to aim for.
In general, I fix the newgen size mostly to avoid the optimizer choosing something braindead in a pathological case. 50/50 is safe, but not optimal.
In general, you should have enough unallocated memory on the box to cover your working dataset (it'll get used by caches and memmaps). If you can, find a way to exploit data locality. I shoot for (number of cores * 1-4)-ish partitions per box depending on workload. Using bigger boxes is usually better, because you can avoid communication latency and variance that arises from having tons of boxes.
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