Guava ImmutableMap noticably slower access than HashMap

[tselyanko]

While working on a memory benchmark of some high-throughput data structures, I realized I could use an \[code\]ImmutableMap\[/code\] with only a little refactoring. Thinking this would be an improvement, I threw it into the mix and was surprised to discover that not only was it slower than \[code\]HashMap\[/code\], in a single-threaded environment it appears to be consistently slower even than \[code\]ConcurrentHashMap\[/code\]!You can see the full benchmark here: https://gist.github.com/dimo414/5290165The meat of the test is pretty simple, time how long it takes to get a large number of random strings that may exist in the map.\[code\]public static void timeAccess(Map<String,String> map) { Random rnd = new Random(seed); int foundCount = 0; long start = System.nanoTime(); for(int i = 0; i < loop; i++) { String s = map.get(RndString.build(rnd)); if(s != null) foundCount++; } long stop = System.nanoTime() - start; System.out.println("Found "+foundCount+" strings out of "+loop+" attempts - "+ String.format("%.2f",100.0*foundCount/loop)+" success rate."); System.out.println(map.getClass().getSimpleName()+" took "+ String.format("%.4f", stop/1_000_000_000.0)+" seconds."); System.out.println();}\[/code\]And running this against a \[code\]HashMap\[/code\], a \[code\]ConcurrentHashMap\[/code\], and an \[code\]ImmutableMap\[/code\], all containing the same values, consistently showed a dramatic slowdown when using \[code\]ImmutableMap\[/code\] - often upwards of 15% slower. The more sparse the map (i.e. the more often \[code\]map.get()\[/code\] returned null) the greater the disparity. Here's the result of a sample run:\[code\]Found 35312152 strings out of 100000000 attempts - 35.31 success rate.HashMap took 29.4538 seconds.Found 35312152 strings out of 100000000 attempts - 35.31 success rate.ConcurrentHashMap took 32.1465 seconds.Found 35312152 strings out of 100000000 attempts - 35.31 success rate.RegularImmutableMap took 37.9709 seconds.\[/code\]Is this a documented / expected issue? The Guava Docs indicate \[code\]Immutable***\[/code\] is more memory efficient, but says nothing about speed. For slowdowns of this magnitude, I'm inclined to deal with the memory costs and avoid \[code\]Immutable***\[/code\] when speed is an issue (and when isn't it?!). Am I missing something?See also: https://groups.google.com/forum/?fromgroups=#!topic/guava-discuss/I7yPpa5Hlpg