the biggest I found yet is https://github.com/apache/logging-log4j2.git
Xeno Amess <xenoam...@gmail.com> 于2025年5月28日周三 17:17写道： > IMO LinkedHashSet can work, no need to use LinkedHashMap directly... > but I still think it better to see the bottle-neck through real-world > running. so let's just find some really biggy open source java projects > using maven(if can't, maybe we have to craft one?) > > > Martin Desruisseaux <martin.desruisse...@geomatys.com> 于2025年5月28日周三 > 03:52写道： > >> Hello >> >> Le 2025-05-26 à 22 h 55, Sergey Chernov a écrit : >> >> > Just tried the 4.0.0-rc-3 comparing with 3.9.9, it's 4x times slower >> > (!) on a project of ~900 modules (700 of them are jar). >> > >> Regarding performance, some months ago I noticed that Maven contains >> loops over elements of a list with a call to `List.contains(…)` inside >> the loop. Because `List.contains(…)` itself iterates over the elements, >> we implicitly have nested loops, which have a performance cost of O(N²) >> where N is the number of elements. Replacing some `ArrayList` by >> `LinkedHashMap` may change some O(N²) operations into O(N) operations. >> The difference between O(N) and O(N²) is unnoticeable when N is small (I >> guess that this is the case of Maven's test suite). But when N become >> large enough, the difference between O(N) or O(N²) can become the >> difference between completing an operation in a few minutes or requiring >> the age of the univers. >> >> I did not verified if Maven 4 has more nested loops than Maven 3. >> Neither I verified if the nested loops happen in algorithms where N can >> possibly be large. We do not need (neither we should) replace all >> `ArrayList` by `LinkedHashMap`. However, I'm not sure if we have >> investigated where such replacements should be done. We may not be able >> to do this investigation now, but we could keep the door open for future >> performance improvements by replacing `List` by `Collection` in the API. >> Even if the implementation stay `ArrayList` for now, it would allow us >> to replace some of them by `LinkedHashMap` in the future if we identify >> that it could bring a performance benefit. >> >> However, an objection to this proposal was that the order of elements >> matter. We had no good solution in Java 17. But if the upgrade to Java >> 21, proposed in a separated thread, is accepted, Maven could replace all >> methods returning `java.util.List` by methods returning >> `java.util.SequencedCollection` in the API. No change in the >> implementation would be done at this stage (we keep the current >> `ArrayList`), but a future Maven version would have more flexibility for >> addressing the O(N²) kind of bottleneck, if any. >> >> Martin >> >>
