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(Updated April 20, 2017, 5:01 p.m.) Review request for mesos, Benjamin Bannier, Benjamin Mahler, and Michael Park. Changes ------- Address review comments. Repository: mesos Description ------- This commit replaces the sorter's flat list of clients with a tree; the tree represents the hierarchical relationship between sorter clients. Each node in the tree contains a vector of pointers to child nodes. The tree might contain nodes that do not correspond directly to sorter clients. For example, adding clients "a/b" and "c/d" results in the following tree: root -> a -> b -> c -> d The `sort` member function still only returns one result for each active client in the sorter. This is implemented by ensuring that each sorter client is associated with a leaf node in the tree. Note that it is possible for a leaf node to be transformed into an internal node by a subsequent insertion; to handle this case, we "implicitly" create an extra child node, which maintains the invariant that each client has a leaf node. For example, if the client "a/b/x" is added to the tree above, the result is: root -> a -> b -> . -> x -> c -> d The "." leaf node holds the allocation that has been made to the "a/b" client itself; the "a/b" node holds the sum of all the allocations that have been made to the subtree rooted at "a/b", which also includes "a/b/x". This commit also introduces a new approach to sorting: rather than keeping an `std::set` of sorter clients, we now keep a tree of `std::vector`, which is sorted explicitly via `std::sort`. The previous implementation tried to optimize the sorting process by updating the sort order incrementally when a single sorter client was updated; this commit removes that optimization, and instead re-sorts the entire tree whenever the sort order is changed. Re-introducing a version of this optimization would make sense in the future (MESOS-7390), but benchmarking suggests that this commit results in a net improvement in sorter performance anyway. The sorter perf improvement is likely due to the introduction of a secondary hashmap that allows the leaf node associated with a tree path to be find efficiently; the previous implementation required a linear scan of a `std::set`. Diffs (updated) ----- src/master/allocator/sorter/drf/metrics.cpp 15aab32db5ca1a7a14080e9bbb7c65283be3ec20 src/master/allocator/sorter/drf/sorter.hpp 76329220e1115c1de7810fb69b943c78c078be59 src/master/allocator/sorter/drf/sorter.cpp ed54680cecb637931fc344fbcf8fd3b14cc24295 src/master/allocator/sorter/sorter.hpp b3029fcf7342406955760da53f1ae736769f308c src/tests/hierarchical_allocator_tests.cpp 33e7b455f8664858eb4f03727b076a10c80cd6e0 src/tests/master_allocator_tests.cpp 119e318f8a01d50e8dae5c30cf5fa6a017c3c625 src/tests/sorter_tests.cpp 43bd85798aef0c89751b725ebf35308a5e9e997a Diff: https://reviews.apache.org/r/57254/diff/21/ Changes: https://reviews.apache.org/r/57254/diff/20-21/ Testing ------- Thanks, Neil Conway