Empty guava cache size?

Question

Just wondering if the system pre-allocate any space for empty guava cache? I am new to guava cache, can someone help me to understand this problem?

Also I test it with code below:

    long preMemUsage = Runtime.getRuntime().totalMemory() -Runtime.getRuntime().freeMemory();
    Cache<String, CountObject> cache = CacheBuilder.newBuilder()
        .maximumSize(12000)
        .expireAfterAccess(7200,TimeUnit.SECONDS)
        .concurrencyLevel(10)
        .recordStats().build();
    try {
        Thread.sleep(1000);
    } catch (InterruptedException e) {
        e.printStackTrace();
    }
    long postMemUsage = Runtime.getRuntime().totalMemory() - Runtime.getRuntime().freeMemory();
    System.out.println("Before: " + preMemUsage);
    System.out.println("After: " + postMemUsage);

The weird thing is the used memory is decreased after..... no idea why. Can someone explain this.

Thanks a lot : )

Mysterious are the ways of garbage collector. It's pretty much possible and you should call garbage collector explicitly before trying to calculate used memory. `System.gc()` — JiriS, Nov 29 '16 at 21:34

score 1 · Answer 1 · answered Nov 29 '16 at 21:35

1

Mysterious are the ways of garbage collector. It's pretty much possible and you should call garbage collector explicitly before trying to calculate used memory. Use System.gc() right before calculating preMemUsage and postMemUsage and you should get much more accurate results.

answered Nov 29 '16 at 21:35

JiriS

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I can't see where exactly and how are you calculating `preMemUsage` – JiriS Nov 29 '16 at 22:13
same as postMemUsage, although I don't think System.gc() make any difference, I tried. It turns out the memory usage drops still. : ) – Nathan Nov 29 '16 at 22:54
Have you tried to "wait" (`Thread.sleep`) before the measurement? – JiriS Jan 10 '17 at 07:57

Empty guava cache size?

1 Answers1