net.sf.ehcache
Class Statistics

java.lang.Object
  net.sf.ehcache.Statistics

All Implemented Interfaces:

java.io.Serializable

public class Statistics
extends java.lang.Object
implements 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 Cache.setStatisticsAccuracy(int).

Because this class maintains a reference to an Ehcache, any references held to this class will precent the Ehcache from getting garbage collected.

The STATISTICS_ACCURACY_BEST_EFFORT, STATISTICS_ACCURACY_GUARANTEED and STATISTICS_ACCURACY_NONE constants have the same values as in JSR107.

Version:

$Id: Statistics.java 704 2008-07-13 00:17:52Z gregluck $

Author:

Greg Luck

See Also:

Serialized Form

Field Summary

static int	STATISTICS_ACCURACY_BEST_EFFORT Best efforts accuracy setting.
static int	STATISTICS_ACCURACY_GUARANTEED Guaranteed accuracy setting.
static int	STATISTICS_ACCURACY_NONE Fast but not accurate setting.

Constructor Summary

Statistics(Ehcache cache, int statisticsAccuracy, long cacheHits, long onDiskHits, long inMemoryHits, long misses, long size, float averageGetTime, long evictionCount)
Creates a new statistics object, associated with a Cache

Method Summary

void	clearStatistics() Clears the statistic counters to 0 for the associated Cache.
Ehcache	getAssociatedCache()
java.lang.String	getAssociatedCacheName()
float	getAverageGetTime() The average get time.
long	getCacheHits() The number of times a requested item was found in the cache.
long	getCacheMisses()
long	getEvictionCount() Gets the number of cache evictions, since the cache was created, or statistics were cleared.
long	getInMemoryHits() Number of times a requested item was found in the Memory Store.
long	getObjectCount() Gets the number of elements stored in the cache.
long	getOnDiskHits() Number of times a requested item was found in the Disk Store.
int	getStatisticsAccuracy() Accurately measuring statistics can be expensive.
java.lang.String	getStatisticsAccuracyDescription() Accurately measuring statistics can be expensive.
java.lang.String	toString() Returns a String representation of the Ehcache statistics.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Field Detail

STATISTICS_ACCURACY_NONE

public static final int STATISTICS_ACCURACY_NONE

Fast but not accurate setting.

See Also:

Constant Field Values

STATISTICS_ACCURACY_BEST_EFFORT

public static final int STATISTICS_ACCURACY_BEST_EFFORT

Best efforts accuracy setting.

See Also:

Constant Field Values

STATISTICS_ACCURACY_GUARANTEED

public static final int STATISTICS_ACCURACY_GUARANTEED

Guaranteed accuracy setting.

See Also:

Constant Field Values

Constructor Detail

Statistics

public Statistics(Ehcache cache,
                  int statisticsAccuracy,
                  long cacheHits,
                  long onDiskHits,
                  long inMemoryHits,
                  long misses,
                  long size,
                  float averageGetTime,
                  long evictionCount)

Creates a new statistics object, associated with a Cache

Parameters:

cache - The cache that clearStatistics() will call, if not disconnected

statisticsAccuracy -

cacheHits -

onDiskHits -

inMemoryHits -

misses -

size -

Method Detail

clearStatistics

public void clearStatistics()

Clears the statistic counters to 0 for the associated Cache.

getCacheHits

public long getCacheHits()

The number of times a requested item was found in the cache.

Returns:

the number of times a requested item was found in the cache

getInMemoryHits

public long getInMemoryHits()

Number of times a requested item was found in the Memory Store.

Returns:

the number of times a requested item was found in memory

getOnDiskHits

public long getOnDiskHits()

Number of times a requested item was found in the Disk Store.

Returns:

the number of times a requested item was found on Disk, or 0 if there is no disk storage configured.

getCacheMisses

public long getCacheMisses()

Returns:

the number of times a requested element was not found in the cache

getObjectCount

public long getObjectCount()

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 STATISTICS_ACCURACY_BEST_EFFORT.

The size is the number of Elements in the MemoryStore plus the number of Elements in the 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 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 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.

Returns:

the number of elements in the ehcache, with a varying degree of accuracy, depending on accuracy setting.

getStatisticsAccuracy

public int getStatisticsAccuracy()

Accurately measuring statistics can be expensive. Returns the current accuracy setting.

Returns:

one of STATISTICS_ACCURACY_BEST_EFFORT, STATISTICS_ACCURACY_GUARANTEED, STATISTICS_ACCURACY_NONE

getStatisticsAccuracyDescription

public java.lang.String getStatisticsAccuracyDescription()

Accurately measuring statistics can be expensive. Returns the current accuracy setting.

Returns:

a human readable description of the accuracy setting. One of "None", "Best Effort" or "Guaranteed".

getAssociatedCacheName

public java.lang.String getAssociatedCacheName()

Returns:

the name of the Ehcache, or null if a reference is no longer held to the cache, as, it would be after deserialization.

getAssociatedCache

public Ehcache getAssociatedCache()

Returns:

the name of the Ehcache, or null if a reference is no longer held to the cache, as, it would be after deserialization.

toString

public final java.lang.String toString()

Returns a String representation of the Ehcache statistics.

Overrides:

toString in class java.lang.Object

getAverageGetTime

public float getAverageGetTime()

The average get time. Because ehcache support JDK1.4.2, each get time uses System.currentTimeMilis, rather than nanoseconds. The accuracy is thus limited.

getEvictionCount

public long getEvictionCount()

Gets the number of cache evictions, since the cache was created, or statistics were cleared.