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Benedict edited comment on CASSANDRA-14660 at 8/23/18 11:40 PM: ---------------------------------------------------------------- bq. In HasMultimap the value collection is a HashSet, which does not work for us. E.g getting tokens for a specific endpoints will not give us sorted token anymore. {{MultimapBuilder}} can be used to construct a {{Multimap}} with hashed keys and {{TreeSet}} values. We would not want to use the {{build(Multimap<K, V>)}} method, as it invokes {{put(K, V)}} for each entry, but if we instead iterated over {{asMap().entrySet()}} and added each {{TreeSet}} individually, we should get the linear complexity construction of the {{TreeSet}} containers. Thinking about it, it's possible this change alone (iterating over {{asMap().entrySet()}}) would be sufficient to restore adequate performance, even if we continued to maintain a {{TreeMap}} for the key lookup (i.e. continued to use a {{TreeMultimap}}). This should be a 3 line change, in {{SortedBiMultiValMap}} and tide us over until we can properly overhaul {{TokenMetadata}}, and have no wider semantic implications to worry about. was (Author: benedict): bq. In HasMultimap the value collection is a HashSet, which does not work for us. E.g getting tokens for a specific endpoints will not give us sorted token anymore. {{MultimapBuilder}} can be used to construct a {{Multimap}} with hashed keys and {{TreeSet}} values. We would not want to use the {{build(Multimap<K, V>)}} method, as it invokes {{put(K, V)}} for each entry, but if we instead iterated over {{asMap().entrySet()}} and added each {{TreeSet}} individually, we should get the linear complexity construction of the {{TreeSet}} containers. Thinking about it, it's probable this change alone (iterating over {{asMap().entrySet()}}) would be sufficient to restore adequate performance, even if we continued to maintain a {{TreeMap}} for the key lookup (i.e. continued to use a {{TreeMultimap}}). This should be a 3 line change, in {{SortedBiMultiValMap}} and tide us over until we can properly overhaul {{TokenMetadata}}, and have no wider semantic implications to worry about. > Improve TokenMetaData cache populating performance for large cluster > -------------------------------------------------------------------- > > Key: CASSANDRA-14660 > URL: https://issues.apache.org/jira/browse/CASSANDRA-14660 > Project: Cassandra > Issue Type: Improvement > Components: Coordination > Environment: Benchmark is on MacOSX 10.13.5, 2017 MBP > Reporter: Pengchao Wang > Priority: Critical > Labels: Performance > Fix For: 3.0.x, 3.11.x, 4.x > > Attachments: 14660-trunk.txt, TokenMetaDataBenchmark.java > > > TokenMetaData#cachedOnlyTokenMap is a method C* used to get a consistent > token and topology view on coordinations without paying read lock cost. Upon > first read the method acquire a synchronize lock and generate a copy of major > token meta data structures and cached it, and upon every token meta data > changes(due to gossip changes), the cache get cleared and next read will > taking care of cache population. > For small to medium size clusters this strategy works pretty well. But large > clusters can actually be suffered from the locking since cache populating is > much slower. On one of our largest cluster (~1000 nodes, 125k tokens, C* > 3.0.15) each cache population take about 500~700ms, and during that there > are no requests can go through since synchronize lock was acquired. This > caused waves of timeouts errors when there are large amount gossip messages > propagating cross the cluster, such as in the case of cluster restarting. > Base on profiling we found that the cost mostly comes from copying > tokenToEndpointMap. It is a SortedBiMultiValueMap made from a forward map use > TreeMap and a reverse map use guava TreeMultiMap. There is an optimization in > TreeMap helps reduce copying complexity from O(N*log(N)) to O(N) when copying > from already ordered data. But guava's TreeMultiMap copying missed that > optimization and make it ~10 times slower than it actually need to be on our > size of cluster. > The patch attached to the issue replace the reverse TreeMultiMap<K, V> to a > vanilla TreeMap<K, TreeSet<V>> in SortedBiMultiValueMap to make sure we can > copy it O(N) time. > I also attached a benchmark script (TokenMetaDataBenchmark.java), which > simulates a large cluster then measures average latency for TokenMetaData > cache populating. > Benchmark result before and after that patch: > {code:java} > trunk: > before 100ms, after 13ms > 3.0.x: > before 199ms, after 15ms > {code} > (On 3.0.x even the forward TreeMap copying is slow, the O(N*log(N)) to O(N) > optimization is not applied because the key comparator is dynamically created > and TreeMap cannot determine the source and dest are in same order) -- This message was sent by Atlassian JIRA (v7.6.3#76005) --------------------------------------------------------------------- To unsubscribe, e-mail: commits-unsubscr...@cassandra.apache.org For additional commands, e-mail: commits-h...@cassandra.apache.org