Low GC in Java: Using primitives

in a recent article i examined how using primitives and collections which support primitives natively instead of wrappers and standard collections can reduce memory usage and improve performance.

different way to have a map of int/integer

there are a number of ways you can use int/integer and a number of collections you store them in. depending on which approach you use can have a big difference on the performance and the amount of garbage produced.

test	performance range	memory used
use integer wrappers and hashmap	71 - 134 (ns)	53 mb/sec
use int primitives and hashmap	45 - 76 (ns)	36 mb/sec
use int primitives and fastmap	58 - 93 (ns)	28 mb/sec
use int primitives and tintinthashmap	18 - 28 (ns)	nonimal
use int primitives and simple hash map	6 - 9 (ns)	nonimal

the performance range was the typical (50%tile) and one of the higher (98%tile) timings. the garbage was the result of 900,000 loops per second.


these tests were run on my new system.

the code

loop tested

int runs = 300 * 300;
for (int i = 0; i < runs; i++) {
    int x = i % 300;
    int y = i / 300;
    int times = x * y;
    integer count = counters.get(times);
    if (count == null)
        counters.put(times, 1);
    else
        counters.put(times, count + 1);
}

directory of performance examples

from http://vanillajava.blogspot.com/2011/07/low-gc-in-java-using-primitives.html