org.apache.jcs.auxiliary.disk.indexed
Class IndexedDiskCache

java.lang.Object
  org.apache.jcs.auxiliary.disk.AbstractDiskCache
      org.apache.jcs.auxiliary.disk.indexed.IndexedDiskCache

All Implemented Interfaces:

java.io.Serializable, AuxiliaryCache, ICache, ICacheType

public class IndexedDiskCache
extends AbstractDiskCache

Disk cache that uses a RandomAccessFile with keys stored in memory. The maximum number of keys stored in memory is configurable. The disk cache tries to recycle spots on disk to limit file expansion.

See Also:

Serialized Form

Nested Class Summary

class

IndexedDiskCache.LRUMap Class for recylcing and lru.

Field Summary

protected EDU.oswego.cs.dl.util.concurrent.ReentrantWriterPreferenceReadWriteLock

storageLock Use this lock to synchronize reads and writes to the underlying storage mechansism.

Fields inherited from class org.apache.jcs.auxiliary.disk.AbstractDiskCache

alive, cacheEventQueue, cacheName, purgatory, purgHits

Fields inherited from interface org.apache.jcs.engine.behavior.ICacheType

CACHE_HUB, DISK_CACHE, LATERAL_CACHE, REMOTE_CACHE

Constructor Summary

IndexedDiskCache(IndexedDiskCacheAttributes cattr)
Constructor for the DiskCache object.

Method Summary

protected boolean	checkForDedOverlaps(IndexedDiskElementDescriptor[] sortedDescriptors) Detects any overlapping elements.
void	doDispose() Dispose of the disk cache in a background thread.
protected ICacheElement	doGet(java.io.Serializable key) Get a value from the persistent store.
boolean	doRemove(java.io.Serializable key) Returns true if the removal was succesful; or false if there is nothing to remove.
void	doRemoveAll() Remove all the items from the disk cache by reseting everything.
void	doUpdate(ICacheElement ce) Update the disk cache.
void	dump() For debugging.
void	dump(boolean dumpValues) For debugging.
AuxiliaryCacheAttributes	getAuxiliaryCacheAttributes() This returns the generic attributes for an auxiliary cache.
protected long	getBytesFree() Returns the number of bytes that are free.
protected long	getDataFileSize() This is for debugging and testing.
java.util.Set	getGroupKeys(java.lang.String groupName) Gets the group keys from the disk.
protected int	getRecyleBinSize() Returns the size of the recyclebin in number of elements.
protected int	getRecyleCount() Returns the number of times we have used spots from the recycle bin.
int	getSize() Returns the current cache size.
IStats	getStatistics() Returns info about the disk cache.
java.lang.String	getStats() Gets basic stats for the disk cache.
protected int	getTimesOptimized() This is exposed for testing.
protected void	loadKeys() Loads the keys from the .key file.
protected void	optimizeFile() File optimization is handled by this method.
protected void	saveKeys() Saves key file to disk.

Methods inherited from class org.apache.jcs.auxiliary.disk.AbstractDiskCache

dispose, get, getCacheName, getCacheType, getStatus, remove, removeAll, update

Methods inherited from class java.lang.Object

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

Field Detail

storageLock

protected EDU.oswego.cs.dl.util.concurrent.ReentrantWriterPreferenceReadWriteLock storageLock

Use this lock to synchronize reads and writes to the underlying storage mechansism.

Constructor Detail

IndexedDiskCache

public IndexedDiskCache(IndexedDiskCacheAttributes cattr)

Constructor for the DiskCache object.

Parameters:

cattr -

Method Detail

loadKeys

protected void loadKeys()
                 throws java.lang.InterruptedException

Loads the keys from the .key file. The keys are stored in a HashMap on disk. This is converted into a LRUMap.

Throws:

java.lang.InterruptedException

checkForDedOverlaps

protected boolean checkForDedOverlaps(IndexedDiskElementDescriptor[] sortedDescriptors)

Detects any overlapping elements. This expects a sorted list.

The total length of an item is IndexedDisk.RECORD_HEADER + ded.len.

Parameters:

sortedDescriptors -

Returns:

false if there are overlaps.

saveKeys

protected void saveKeys()

Saves key file to disk. This converts the LRUMap to a HashMap for deserialzation.

doUpdate

public void doUpdate(ICacheElement ce)

Update the disk cache. Called from the Queue. Makes sure the Item has not been retireved from purgatory while in queue for disk. Remove items from purgatory when they go to disk.

Specified by:

doUpdate in class AbstractDiskCache

Parameters:

ce - The ICacheElement to put to disk.

doGet

protected ICacheElement doGet(java.io.Serializable key)

Description copied from class: AbstractDiskCache

Get a value from the persistent store.

Specified by:

doGet in class AbstractDiskCache

Parameters:

key -

Returns:

ICacheElement or null

See Also:

AbstractDiskCache.doGet(java.io.Serializable)

getGroupKeys

public java.util.Set getGroupKeys(java.lang.String groupName)

Gets the group keys from the disk.

Specified by:

getGroupKeys in interface AuxiliaryCache

Specified by:

getGroupKeys in class AbstractDiskCache

Returns:

a set of group keys

See Also:

AuxiliaryCache.getGroupKeys(java.lang.String)

doRemove

public boolean doRemove(java.io.Serializable key)

Returns true if the removal was succesful; or false if there is nothing to remove. Current implementation always result in a disk orphan.

Specified by:

doRemove in class AbstractDiskCache

Parameters:

key -

Returns:

true if at least one item was removed.

doRemoveAll

public void doRemoveAll()

Remove all the items from the disk cache by reseting everything.

Specified by:

doRemoveAll in class AbstractDiskCache

doDispose

public void doDispose()

Dispose of the disk cache in a background thread. Joins against this thread to put a cap on the disposal time.

Specified by:

doDispose in class AbstractDiskCache

optimizeFile

protected void optimizeFile()

File optimization is handled by this method. It works as follows:

1. Shutdown recycling and turn on queuing of puts.
2. Take a snapshot of the current descriptors. If there are any removes, ignore them, as they will be compacted during the next optimization.
3. Optimize the snapshot. For each descriptor:
   1. Obtain the write-lock.
   2. Shift the element on the disk, in order to compact out the free space.
   3. Release the write-lock. This allows elements to still be accessible during optimization.
4. Obtain the write-lock.
5. All queued puts are made at the end of the file. Optimize these under a single write-lock.
6. Truncate the file.
7. Release the write-lock.
8. Restore system to standard operation.

getSize

public int getSize()

Returns the current cache size.

Specified by:

getSize in interface AuxiliaryCache

Specified by:

getSize in interface ICache

Specified by:

getSize in class AbstractDiskCache

Returns:

The size value

See Also:

ICache.getSize()

getRecyleBinSize

protected int getRecyleBinSize()

Returns the size of the recyclebin in number of elements.

Returns:

The number of items in the bin.

getRecyleCount

protected int getRecyleCount()

Returns the number of times we have used spots from the recycle bin.

Returns:

The number of spots used.

getBytesFree

protected long getBytesFree()

Returns the number of bytes that are free. When an item is removed, its length is recorded. When a spot is used form the recycle bin, the length of the item stored is recorded.

Returns:

The number bytes free on the disk file.

getDataFileSize

protected long getDataFileSize()
                        throws java.io.IOException

This is for debugging and testing.

Returns:

the length of the data file.

Throws:

java.io.IOException

dump

public void dump()

For debugging. This dumps the values by defualt.

dump

public void dump(boolean dumpValues)

For debugging.

Parameters:

dumpValues - A boolean indicating if values should be dumped.

getAuxiliaryCacheAttributes

public AuxiliaryCacheAttributes getAuxiliaryCacheAttributes()

Description copied from interface: AuxiliaryCache

This returns the generic attributes for an auxiliary cache. Most implementations will cast this to a more specific type.

Returns:

Returns the AuxiliaryCacheAttributes.

getStats

public java.lang.String getStats()

Gets basic stats for the disk cache.

Specified by:

getStats in interface ICache

Overrides:

getStats in class AbstractDiskCache

Returns:

String

getStatistics

public IStats getStatistics()

Returns info about the disk cache.

(non-Javadoc)

Specified by:

getStatistics in interface AuxiliaryCache

Overrides:

getStatistics in class AbstractDiskCache

Returns:

See Also:

AuxiliaryCache.getStatistics()

getTimesOptimized

protected int getTimesOptimized()

This is exposed for testing.

Returns:

Returns the timesOptimized.