Hello everyone, This morning I investigated with Vincent Blondeau a problem reported by the Moose community a while ago: loading Moose model is slower in Spur (Pharo 5+) than in pre-Spur (Pharo 4 and older). In general, this problem was present for anyone growing images to a significant size. To investigate the problem, we loaded a 200Mb[3] Moose model on a 250Mb image, growing the image to 450Mb. Loading such a model takes 2 minutes in Spur and 1m30s in pre-Spur VMs. Using the stable Pharo VM, the analysis results were the following: - total time spent to load the Model: 2 minutes - time spent in full GC: 1 minute (4 fullGCs) - time spent in scavenges[1]: 15 seconds On the 2 minutes spent, we have 50% of the time spent in full GCs, 12.5% in scavenges, 37.5% executing code. We then used the latest VM that features the new compactor (VM from beginning of March 2017 and over). The full GC execution time went down from 1 minute to 2 seconds. In addition, we increased the size of Eden[2] from 4Mb to 12Mb. Time spent in scavenges decreased from 15 seconds to 5 seconds. Overall, loading the model is now taking ~50 seconds instead of 2 minutes. To increase Eden size, one needs to run a script similar to: | currentEdenSize desiredEdenSize | currentEdenSize := Smalltalk vm parameterAt: 44. desiredEdenSize := currentEdenSize * 4. Smalltalk vm parameterAt: 45 put: desiredEdenSize. *And then restart the image.* I hope this report can be useful for some of you. I will try to make a blog post out of it, detailing other GC settings one can change from the image to improve performance. Best, Clement [1] A scavenge is basically the garbage collection of only young objects [2] Eden is basically the space where objects are initially allocated. [3] All numbers in the report are order of magnitudes and not precise numbers