Ehcache 3 size in memory

Question

In Ehcache 2, it was possible to get the size in memory using calculateInMemorySize() e.g.:

CacheManager manager = CacheManager.create();
Cache cache = new Cache(
    new CacheConfiguration("test", 100)
        .eternal(true)
        .statistics(true));
manager.addCache(cache);

assertEquals(0, cache.calculateInMemorySize());

cache.put(new Element(0, "A"));
cache.put(new Element(1, "B"));
cache.put(new Element(2, "C"));

assertTrue(cache.calculateInMemorySize() > 0);
manager.shutdown();

What is the equivalent in Ehcache 3.6.1?

In the following, the getOccupiedByteSize() method returns -1:

StatisticsService statisticsService = new DefaultStatisticsService();
CacheManager manager = CacheManagerBuilder.newCacheManagerBuilder()
    .using(statisticsService)
    .build(true);

CacheConfiguration<Integer, String> config =
    CacheConfigurationBuilder.newCacheConfigurationBuilder(
        Integer.class, String.class, ResourcePoolsBuilder.heap(100))
            .withExpiry(ExpiryPolicy.NO_EXPIRY)
            .build();

Cache<Integer, String> cache = manager.createCache("test", config);

cache.put(0, "A");
cache.put(1, "B");
cache.put(2, "C");

CacheStatistics stats = statisticsService.getCacheStatistics("test");
TierStatistics heap = stats.getTierStatistics().get("OnHeap");
assertTrue(heap.getOccupiedByteSize() > 0);
manager.close();

It does work for a memory unit limited cache. e.g. when the cache configuration is:

CacheConfiguration<Integer, String> config =
    CacheConfigurationBuilder.newCacheConfigurationBuilder(
        Integer.class, String.class,
        ResourcePoolsBuilder.newResourcePoolsBuilder().heap(100, MemoryUnit.MB))
            .withExpiry(ExpiryPolicy.NO_EXPIRY).build();

This is not desirable as the cache must be configured with an element limit, not a memory limit.

---

As per Henri's answer below, it is possible to get the memory size using Sizeof.deepSizeOf(), however some knowledge of the cache implementation is required to exclude unwanted objects e.g.:

SizeOfFilter ehcache = new SizeOfFilter() {
    @Override
    public Collection<Field> filterFields(Class<?> klazz, Collection<Field> fields) {
        if (EhcacheBase.class.isAssignableFrom(klazz)) {
            for (Field field : fields) {
                if ("store".equals(field.getName())) {
                    return Collections.singletonList(field);
                }
            }
            return Collections.emptyList();
        }
        return fields;
    }

    @Override
    public boolean filterClass(Class<?> klazz) {
        return true;
    }
};

SizeOf sizeOf = SizeOf.newInstance(ehcache);
long size = sizeOf.deepSizeOf(cache);

There is an enhancement request to simplify it here: https://github.com/ehcache/ehcache3/issues/2500

Answer 1

It's not possible. By design.

We do not calculate size when the limit is entries. For performance reason. Keeping track of the size is quite costly.

However, I think in your case, I would do a sizeof. If you don't need it that often, just do a sizeof of the cache and it will give you the current cache size nicely.

SizeOf sizeOf = SizeOf.newInstance();
long deepSize = sizeOf.deepSizeOf(cache); // in bytes