Low GC in Java: Using primitives

Overview

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);
}

Link to all the code is here

Directory of performance examples