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/**
* Copyright 2003-2006 Greg Luck
*
* 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 net.sf.ehcache;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import java.io.Serializable;
/**
* An immutable Cache statistics implementation}
*
* This is like a value object, with the added ability to clear cache statistics on the cache.
* That ability does not survive any Serialization of this class. On deserialization the cache
* can be considered disconnected.
*
* The accuracy of these statistics are determined by the value of {#getStatisticsAccuracy()}
* at the time the statistic was computed. This can be changed by setting {@link Cache#setStatisticsAccuracy}.
*
* Because this class maintains a reference to an Ehcache, any references held to this class will precent the Ehcache
* from getting garbage collected.
*
* @author Greg Luck
* @version $Id: Statistics.java 173 2006-08-21 07:04:28Z gregluck $
*/
public class Statistics implements Serializable {
/**
* Best efforts accuracy setting.
*/
public static final int STATISTICS_ACCURACY_BEST_EFFORT = 0;
/**
* Guaranteed accuracy setting.
*/
public static final int STATISTICS_ACCURACY_GUARANTEED = 1;
/**
* Fast but not accurate setting.
*/
public static final int STATISTICS_ACCURACY_NONE = 2;
private static final Log LOG = LogFactory.getLog(Statistics.class.getName());
private static final long serialVersionUID = 3606940454221918725L;
private transient Ehcache cache;
private final int statisticsAccuracy;
private final int cacheHits;
private final int onDiskHits;
private final int inMemoryHits;
private final int misses;
private final int size;
/**
* Creates a new statistics object, associated with a Cache
*
* @param cache The cache that {@link #clearStatistics()} will call, if not disconnected
* @param statisticsAccuracy
* @param cacheHits
* @param onDiskHits
* @param inMemoryHits
* @param misses
* @param size
*/
public Statistics(Ehcache cache, int statisticsAccuracy, int cacheHits, int onDiskHits, int inMemoryHits,
int misses, int size) {
this.statisticsAccuracy = statisticsAccuracy;
this.cacheHits = cacheHits;
this.onDiskHits = onDiskHits;
this.inMemoryHits = inMemoryHits;
this.misses = misses;
this.cache = cache;
this.size = size;
}
/**
* Clears the statistic counters to 0 for the associated Cache.
*/
public void clearStatistics() {
if (cache == null) {
throw new IllegalStateException("This statistics object no longer references a Cache.");
}
try {
cache.clearStatistics();
} catch (IllegalStateException e) {
if (LOG.isDebugEnabled()) {
LOG.info("Ignoring call because " + e.getMessage());
}
}
}
/**
* The number of times a requested item was found in the cache.
*
* @return the number of times a requested item was found in the cache
*/
public int getCacheHits() {
return cacheHits;
}
/**
* Number of times a requested item was found in the Memory Store.
*
* @return the number of times a requested item was found in memory
*/
public int getInMemoryHits() {
return inMemoryHits;
}
/**
* Number of times a requested item was found in the Disk Store.
*
* @return the number of times a requested item was found on Disk, or 0 if there is no disk storage configured.
*/
public int getOnDiskHits() {
return onDiskHits;
}
/**
* @return the number of times a requested element was not found in the cache
*/
public int getCacheMisses() {
return misses;
}
/**
* Gets the number of elements stored in the cache. Caclulating this can be expensive. Accordingly,
* this method will return three different values, depending on the statistics accuracy setting.
* Best Effort Size
* This result is returned when the statistics accuracy setting is {@link Statistics#STATISTICS_ACCURACY_BEST_EFFORT}.
*
* The size is the number of {@link Element}s in the {@link net.sf.ehcache.store.MemoryStore} plus
* the number of {@link Element}s in the {@link net.sf.ehcache.store.DiskStore}.
*
* This number is the actual number of elements, including expired elements that have
* not been removed. Any duplicates between stores are accounted for.
*
* Expired elements are removed from the the memory store when
* getting an expired element, or when attempting to spool an expired element to
* disk.
*
* Expired elements are removed from the disk store when getting an expired element,
* or when the expiry thread runs, which is once every five minutes.
*
* Guaranteed Accuracy Size
* This result is returned when the statistics accuracy setting is {@link Statistics#STATISTICS_ACCURACY_GUARANTEED}.
*
* This method accounts for elements which might be expired or duplicated between stores. It take approximately
* 200ms per 1000 elements to execute.
* Fast but non-accurate Size
* This result is returned when the statistics accuracy setting is {@link #STATISTICS_ACCURACY_NONE}.
*
* The number given may contain expired elements. In addition if the DiskStore is used it may contain some double
* counting of elements. It takes 6ms for 1000 elements to execute. Time to execute is O(log n). 50,000 elements take
* 36ms.
*
* @return the number of elements in the ehcache, with a varying degree of accuracy, depending on accuracy setting.
*/
public int getObjectCount() {
return size;
}
/**
* Accurately measuring statistics can be expensive. Returns the current accuracy setting.
*
* @return one of {@link #STATISTICS_ACCURACY_BEST_EFFORT}, {@link #STATISTICS_ACCURACY_GUARANTEED}, {@link #STATISTICS_ACCURACY_NONE}
*/
public int getStatisticsAccuracy() {
return statisticsAccuracy;
}
/**
* @return the name of the Ehcache, or null is there no associated cache
*/
public String getAssociatedCacheName() {
if (cache != null) {
return cache.getName();
} else {
return null;
}
}
/**
* Returns a {@link String} representation of the {@link Ehcache} statistics.
*/
public final String toString() {
StringBuffer dump = new StringBuffer();
dump.append("[ ")
.append(" name = ").append(getAssociatedCacheName())
.append(" cacheHits = ").append(cacheHits)
.append(" onDiskHits = ").append(onDiskHits)
.append(" inMemoryHits = ").append(inMemoryHits)
.append(" misses = ").append(misses)
.append(" size = ").append(size)
.append(" ]");
return dump.toString();
}
}