/*
* Copyright (c) 2008-2017, Hazelcast, Inc. All Rights Reserved.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.hazelcast.cache.impl.maxsize.impl;
import com.hazelcast.cache.impl.record.CacheRecordMap;
import com.hazelcast.internal.eviction.EvictionChecker;
/**
* Cache max-size policy implementation for
* {@link com.hazelcast.config.EvictionConfig.MaxSizePolicy#ENTRY_COUNT}
*/
public class EntryCountCacheEvictionChecker
implements EvictionChecker {
private static final int MAX_ENTRY_COUNT_FOR_THRESHOLD_USAGE = 1000000;
private static final int STD_DEV_OF_5_THRESHOLD = 4000;
private static final int STD_DEV_MULTIPLIER_5 = 5;
private static final int STD_DEV_MULTIPLIER_3 = 3;
private final CacheRecordMap cacheRecordMap;
private final int maxPartitionSize;
public EntryCountCacheEvictionChecker(final int size,
final CacheRecordMap cacheRecordMap, final int partitionCount) {
this.cacheRecordMap = cacheRecordMap;
this.maxPartitionSize = calculateMaxPartitionSize(size, partitionCount);
}
// Defined as "public static" since external tests can test the logic without knowing the logic
// for calculating the estimated max size.
public static int calculateMaxPartitionSize(int maxEntryCount, int partitionCount) {
final double balancedPartitionSize = (double) maxEntryCount / (double) partitionCount;
final double approximatedStdDev = Math.sqrt(balancedPartitionSize);
int stdDevMultiplier;
if (maxEntryCount <= STD_DEV_OF_5_THRESHOLD) {
// Below 4.000 entry count, multiplying standard deviation with 5 gives better estimations
// as our experiments and test results.
stdDevMultiplier = STD_DEV_MULTIPLIER_5;
} else if (maxEntryCount > STD_DEV_OF_5_THRESHOLD
&& maxEntryCount <= MAX_ENTRY_COUNT_FOR_THRESHOLD_USAGE) {
// Above 4.000 entry count but below 1.000.000 entry count,
// multiplying standard deviation with 3 gives better estimations
// as our experiments and test results.
stdDevMultiplier = STD_DEV_MULTIPLIER_3;
} else {
// Over 1.000.000 entries, there is no need for using standard deviation
stdDevMultiplier = 0;
}
return (int) ((approximatedStdDev * stdDevMultiplier) + balancedPartitionSize);
}
@Override
public boolean isEvictionRequired() {
return cacheRecordMap.size() >= maxPartitionSize;
}
}