org.cache2k.impl

Class DepthSearchAndSizeCounter

java.lang.Object

org.cache2k.impl.DepthSearchAndSizeCounter

public class DepthSearchAndSizeCounter
extends Object

Helper to estimate the size of object within a cache. Usage: Insert all objects to analyze with insert(), than call descend() to descend one level of the object graph. The end is reached when hasNext() yields false. The The result can be obtained via getBytes().

The basic problem when we want to estimate the size is that it is never known whether an object is exclusive for our cache structure, or it is also referenced by some other classes. To do a "perfect" size measurement the whole java heap must be analyzed and it must be decided which object should be counted where. So, anyway, let's try a good guess, and see whether it is of some use.

Heuristics: Top-Level objects are always counted at least once by instance. An identical object that is found via different ways when descending the graph is not counted at all. Object reached via a non-counted object are not counted.

Caveats: If only one object contains a reference to a bigger static data structure that belongs to the system, the size could be totally wrong. Countermeasures: we do measure the size only if more then x objects are in the cache and we limit the depth. If objects have a reference e.g. to some system objects, or maybe the cache, these objects will not be counted, if the reference is appearing more than once. So an problem may still arise if there is one object within the cache that holds such a reference and the others not. Current countermeasures for this: Estimate size only when sufficient objects are in the cache; limit the descending depth.

Author:

Jens Wilke; created: 2013-06-25

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	DepthSearchAndSizeCounter.EstimationException

Constructor Summary

Constructors

Constructor and Description
DepthSearchAndSizeCounter()

Method Summary

Methods

Modifier and Type	Method and Description
void	descend()
int	getByteCount()
int	getCounter()
int	getNextCount()
int	getObjectCount()
boolean	hasCircles()
boolean	hasCommonObjects()
boolean	hasNext()
void	insert(Object o)
void	resetCounter() Reset our counters but keep the lookup set of the objects seen so far.

Methods inherited from class java.lang.Object

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

Constructor Detail

DepthSearchAndSizeCounter

public DepthSearchAndSizeCounter()

Method Detail

insert

public void insert(Object o)

getNextCount

public int getNextCount()

hasNext

public boolean hasNext()

descend

public void descend()
             throws DepthSearchAndSizeCounter.EstimationException

Throws:

DepthSearchAndSizeCounter.EstimationException

resetCounter

public void resetCounter()

Reset our counters but keep the lookup set of the objects seen so far.

getByteCount

public int getByteCount()

getObjectCount

public int getObjectCount()

getCounter

public int getCounter()

hasCommonObjects

public boolean hasCommonObjects()

hasCircles

public boolean hasCircles()