Colin Cassidy created IGNITE-12096:
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             Summary: Ignite memory metrics incorrect on cache usage contraction
                 Key: IGNITE-12096
                 URL: https://issues.apache.org/jira/browse/IGNITE-12096
             Project: Ignite
          Issue Type: Bug
          Components: cache
    Affects Versions: 2.7
            Reporter: Colin Cassidy


When using the Ignite metrics API to measure available memory, the usage 
figures appear to be accurate while memory is being consumed - but when memory 
is freed the metrics do not drop. They appear to report that memory has not 
been freed up, even though it has.

Reproducer below. This affects Ignite 2.7+.

{{}}{{import org.apache.ignite.failure.NoOpFailureHandler; }}
{{import org.junit.Test; }}

{{public class MemoryTest2 { }}

{{    private static final String CACHE_NAME = "cache"; }}
{{    private static final String DEFAULT_MEMORY_REGION = "Default_Region"; }}
{{    private static final long MEM_SIZE = 100L * 1024 * 1024; }}


{{    @Test }}
{{    public void testOOM() throws InterruptedException { }}
{{        try (Ignite ignite = startIgnite("IgniteMemoryMonitorTest1")) { }}
{{            fillDataRegion(ignite); }}
{{            CacheConfiguration<Object, Object> cfg = new }}
{{CacheConfiguration<>(CACHE_NAME); }}
{{            cfg.setStatisticsEnabled(true); }}
{{            IgniteCache<Object, Object> cache = }}
{{ignite.getOrCreateCache(cfg); }}

{{            // Clear all entries from the cache to free up memory }}
{{            memUsed(ignite); }}
{{            cache.clear(); }}
{{            cache.removeAll(); }}
{{            cache.put("Key", "Value"); }}
{{            memUsed(ignite); }}
{{            cache.destroy(); }}
{{            Thread.sleep(5000); }}

{{            // Should now report close to 0% but reports 59% still }}
{{            memUsed(ignite); }}
{{        } }}
{{    } }}
{{    }}
{{    private Ignite startIgnite(String instanceName) { }}
{{        IgniteConfiguration cfg = new IgniteConfiguration(); }}
{{        cfg.setIgniteInstanceName(instanceName); }}
{{        cfg.setDataStorageConfiguration(createDataStorageConfiguration()); }}
{{        cfg.setFailureHandler(new NoOpFailureHandler()); }}
{{        return Ignition.start(cfg); }}
{{    } }}

{{    private DataStorageConfiguration createDataStorageConfiguration() { }}
{{        return new DataStorageConfiguration() }}
{{                .setDefaultDataRegionConfiguration( }}
{{                        new DataRegionConfiguration() }}
{{                                .setName(DEFAULT_MEMORY_REGION) }}
{{                                .setInitialSize(MEM_SIZE) }}
{{                                .setMaxSize(MEM_SIZE) }}
{{                                .setMetricsEnabled(true)); }}
{{    } }}

{{    private void fillDataRegion(Ignite ignite) { }}
{{        byte[] megabyte = new byte[1024 * 1024]; }}
{{            IgniteCache<Object, Object> cache = }}
{{                    ignite.getOrCreateCache(CACHE_NAME); }}
{{            for (int i = 0; i < 50; i++) { }}
{{                cache.put(i, megabyte); }}
{{                memUsed(ignite); }}
{{            } }}
{{    } }}

{{    private void memUsed(Ignite ignite) { }}
{{        DataRegionConfiguration defaultDataRegionCfg = }}
{{ignite.configuration() }}
{{                .getDataStorageConfiguration() }}
{{                .getDefaultDataRegionConfiguration(); }}
{{        String regionName = defaultDataRegionCfg.getName(); }}
{{        DataRegionMetrics metrics = ignite.dataRegionMetrics(regionName); }}
{{        float usedMem = metrics.getPagesFillFactor() * }}
{{metrics.getTotalAllocatedPages() * metrics.getPageSize(); }}
{{        float pctUsed = 100 * usedMem / defaultDataRegionCfg.getMaxSize(); }}
{{        System.out.println("Memory used: " + pctUsed + "%"); }}
{{    } }}
{{} }}



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