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434ab2a6a3
This is a fairly easy attempt to dynamically evict chunks based on the heap size. A target heap size has to be set as a command line flage, so that users can essentially say "utilize 4GiB of RAM, and please don't OOM". The -storage.local.max-chunks-to-persist and -storage.local.memory-chunks flags are deprecated by this change. Backwards compatibility is provided by ignoring -storage.local.max-chunks-to-persist and use -storage.local.memory-chunks to set the new -storage.local.target-heap-size to a reasonable (and conservative) value (both with a warning). This also makes the metrics intstrumentation more consistent (in naming and implementation) and cleans up a few quirks in the tests. Answers to anticipated comments: There is a chance that Go 1.9 will allow programs better control over the Go memory management. I don't expect those changes to be in contradiction with the approach here, but I do expect them to complement them and allow them to be more precise and controlled. In any case, once those Go changes are available, this code has to be revisted. One might be tempted to let the user specify an estimated value for the RSS usage, and then internall set a target heap size of a certain fraction of that. (In my experience, 2/3 is a fairly safe bet.) However, investigations have shown that RSS size and its relation to the heap size is really really complicated. It depends on so many factors that I wouldn't even start listing them in a commit description. It depends on many circumstances and not at least on the risk trade-off of each individual user between RAM utilization and probability of OOMing during a RAM usage peak. To not add even more to the confusion, we need to stick to the well-defined number we also use in the targeting here, the sum of the sizes of heap objects. |
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