Low GC in Java: Using primitives

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Low GC in Java: Using primitives

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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);
        counters.put(times, count + 1);
Directory of performance examples


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


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