An implementation of FlatMap container (aka Boost flat_map) in Scala.
In theory it should be easier for GC to copy that map from Eden to S0/S1 and b/w S0/S1 than ordinary map.
It's very bad for modifications (O(N)), but potentialy faster on lookups as it is more cache friendly. In Scala 2.13.x ArraySeq should be used, but I am not as good in Scala to make it happen.
Current values with comparison to java.util.TreeMap and scala.collection.immutable.TreeMap. Absolute values are meaningless unlike relative
[info] Benchmark Mode Cnt Score Error Units
[info] FlatMapBencchmark.lookupAllKeysFlatMap avgt 5 1734926.417 ± 5426.746 ns/op
[info] FlatMapBencchmark.lookupAllKeysFlatMap:·gc.alloc.rate avgt 5 85.250 ± 0.266 MB/sec
[info] FlatMapBencchmark.lookupAllKeysFlatMap:·gc.alloc.rate.norm avgt 5 162848.076 ± 0.010 B/op
[info] FlatMapBencchmark.lookupAllKeysFlatMap:·gc.churn.PS_Eden_Space avgt 5 85.206 ± 8.744 MB/sec
[info] FlatMapBencchmark.lookupAllKeysFlatMap:·gc.churn.PS_Eden_Space.norm avgt 5 162764.538 ± 16907.671 B/op
[info] FlatMapBencchmark.lookupAllKeysFlatMap:·gc.churn.PS_Survivor_Space avgt 5 0.023 ± 0.019 MB/sec
[info] FlatMapBencchmark.lookupAllKeysFlatMap:·gc.churn.PS_Survivor_Space.norm avgt 5 43.203 ± 36.680 B/op
[info] FlatMapBencchmark.lookupAllKeysFlatMap:·gc.count avgt 5 101.000 counts
[info] FlatMapBencchmark.lookupAllKeysFlatMap:·gc.time avgt 5 46.000 ms
[info] FlatMapBencchmark.lookupAllKeysJavaTreeMap avgt 5 977655.465 ± 22091.444 ns/op
[info] FlatMapBencchmark.lookupAllKeysJavaTreeMap:·gc.alloc.rate avgt 5 150.335 ± 3.370 MB/sec
[info] FlatMapBencchmark.lookupAllKeysJavaTreeMap:·gc.alloc.rate.norm avgt 5 161824.045 ± 0.027 B/op
[info] FlatMapBencchmark.lookupAllKeysJavaTreeMap:·gc.churn.PS_Eden_Space avgt 5 150.708 ± 8.244 MB/sec
[info] FlatMapBencchmark.lookupAllKeysJavaTreeMap:·gc.churn.PS_Eden_Space.norm avgt 5 162223.292 ± 6937.536 B/op
[info] FlatMapBencchmark.lookupAllKeysJavaTreeMap:·gc.churn.PS_Survivor_Space avgt 5 0.048 ± 0.048 MB/sec
[info] FlatMapBencchmark.lookupAllKeysJavaTreeMap:·gc.churn.PS_Survivor_Space.norm avgt 5 51.882 ± 50.779 B/op
[info] FlatMapBencchmark.lookupAllKeysJavaTreeMap:·gc.count avgt 5 193.000 counts
[info] FlatMapBencchmark.lookupAllKeysJavaTreeMap:·gc.time avgt 5 94.000 ms
[info] FlatMapBencchmark.lookupAllKeysTreeMap avgt 5 1242862.975 ± 29797.255 ns/op
[info] FlatMapBencchmark.lookupAllKeysTreeMap:·gc.alloc.rate avgt 5 237.985 ± 5.710 MB/sec
[info] FlatMapBencchmark.lookupAllKeysTreeMap:·gc.alloc.rate.norm avgt 5 325664.054 ± 0.001 B/op
[info] FlatMapBencchmark.lookupAllKeysTreeMap:·gc.churn.PS_Eden_Space avgt 5 237.374 ± 6.744 MB/sec
[info] FlatMapBencchmark.lookupAllKeysTreeMap:·gc.churn.PS_Eden_Space.norm avgt 5 324833.062 ± 9317.296 B/op
[info] FlatMapBencchmark.lookupAllKeysTreeMap:·gc.churn.PS_Survivor_Space avgt 5 0.047 ± 0.039 MB/sec
[info] FlatMapBencchmark.lookupAllKeysTreeMap:·gc.churn.PS_Survivor_Space.norm avgt 5 64.350 ± 53.859 B/op
[info] FlatMapBencchmark.lookupAllKeysTreeMap:·gc.count avgt 5 304.000 counts
[info] FlatMapBencchmark.lookupAllKeysTreeMap:·gc.time avgt 5 140.000 ms
[info] FlatMapBencchmark.lookupSeveralKeysFlatMap avgt 5 208.507 ± 9.639 ns/op
[info] FlatMapBencchmark.lookupSeveralKeysFlatMap:·gc.alloc.rate avgt 5 209.107 ± 9.514 MB/sec
[info] FlatMapBencchmark.lookupSeveralKeysFlatMap:·gc.alloc.rate.norm avgt 5 48.000 ± 0.001 B/op
[info] FlatMapBencchmark.lookupSeveralKeysFlatMap:·gc.churn.PS_Eden_Space avgt 5 209.281 ± 8.225 MB/sec
[info] FlatMapBencchmark.lookupSeveralKeysFlatMap:·gc.churn.PS_Eden_Space.norm avgt 5 48.042 ± 1.750 B/op
[info] FlatMapBencchmark.lookupSeveralKeysFlatMap:·gc.churn.PS_Survivor_Space avgt 5 0.014 ± 0.022 MB/sec
[info] FlatMapBencchmark.lookupSeveralKeysFlatMap:·gc.churn.PS_Survivor_Space.norm avgt 5 0.003 ± 0.005 B/op
[info] FlatMapBencchmark.lookupSeveralKeysFlatMap:·gc.count avgt 5 268.000 counts
[info] FlatMapBencchmark.lookupSeveralKeysFlatMap:·gc.time avgt 5 127.000 ms
[info] FlatMapBencchmark.lookupSeveralKeysTreeMap avgt 5 154.476 ± 1.770 ns/op
[info] FlatMapBencchmark.lookupSeveralKeysTreeMap:·gc.alloc.rate avgt 5 94.071 ± 1.077 MB/sec
[info] FlatMapBencchmark.lookupSeveralKeysTreeMap:·gc.alloc.rate.norm avgt 5 16.000 ± 0.001 B/op
[info] FlatMapBencchmark.lookupSeveralKeysTreeMap:·gc.churn.PS_Eden_Space avgt 5 94.451 ± 3.942 MB/sec
[info] FlatMapBencchmark.lookupSeveralKeysTreeMap:·gc.churn.PS_Eden_Space.norm avgt 5 16.065 ± 0.597 B/op
[info] FlatMapBencchmark.lookupSeveralKeysTreeMap:·gc.churn.PS_Survivor_Space avgt 5 0.019 ± 0.025 MB/sec
[info] FlatMapBencchmark.lookupSeveralKeysTreeMap:·gc.churn.PS_Survivor_Space.norm avgt 5 0.003 ± 0.004 B/op
[info] FlatMapBencchmark.lookupSeveralKeysTreeMap:·gc.count avgt 5 116.000 counts
[info] FlatMapBencchmark.lookupSeveralKeysTreeMap:·gc.time avgt 5 57.000 ms