org.exist.storage
Class CacheManager

java.lang.Object
  org.exist.storage.CacheManager

public class CacheManager

extends java.lang.Object

CacheManager maintains a global memory pool available to all page caches. All caches start with a low default setting, but CacheManager can grow individual caches until the total memory is reached. Caches can also be shrinked if their "load" remains below a given threshold between check intervals.The check interval is determined by the global sync background thread. The class computes the available memory in terms of pages.

Author:

wolf

Field Summary

static double	MAX_MEM_USE The maximum fraction of the total memory that can be used by a single cache.
static double	MIN_SHRINK_FACTOR The minimum size a cache needs to have to be considered for shrinking, defined in terms of a fraction of the overall memory.
static double	SHRINK_FACTOR The amount by which a large cache will be shrinked if other caches request a resize.
static int	SHRINK_THRESHOLD The minimum number of pages that must be read from a cache between check intervals to be not considered for shrinking.

Constructor Summary

CacheManager(Configuration config)

Method Summary

void	checkCaches() Called from the global major sync event to check if caches can be shrinked.
void	checkDistribution() Called from the global minor sync event to check if a smaller cache wants to be resized.
void	deregisterCache(Cache cache)
int	getDefaultInitialSize() Returns the default initial size for all caches.
void	registerCache(Cache cache) Register a cache, i.e.
int	requestMem(Cache cache) Called by a cache if it wants to grow.

Methods inherited from class java.lang.Object

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

Field Detail

MAX_MEM_USE

public static final double MAX_MEM_USE

The maximum fraction of the total memory that can be used by a single cache.

See Also:

Constant Field Values

MIN_SHRINK_FACTOR

public static final double MIN_SHRINK_FACTOR

The minimum size a cache needs to have to be considered for shrinking, defined in terms of a fraction of the overall memory.

See Also:

Constant Field Values

SHRINK_FACTOR

public static final double SHRINK_FACTOR

The amount by which a large cache will be shrinked if other caches request a resize.

See Also:

Constant Field Values

SHRINK_THRESHOLD

public static final int SHRINK_THRESHOLD

The minimum number of pages that must be read from a cache between check intervals to be not considered for shrinking. This is a measure for the "load" of the cache. Caches with high load will never be shrinked.

See Also:

Constant Field Values

Constructor Detail

CacheManager

public CacheManager(Configuration config)

Method Detail

registerCache

public void registerCache(Cache cache)

Register a cache, i.e. put it under control of the cache manager.

Parameters:

cache -

deregisterCache

public void deregisterCache(Cache cache)

requestMem

public int requestMem(Cache cache)

Called by a cache if it wants to grow. The cache manager will either deny the request, for example, if there are no spare pages left, or calculate a new cache size and call the cache's Cache.resize(int) method to resize the cache. The amount of pages by which the cache will grow is determined by the cache's growthFactor: Cache.getGrowthFactor().

Parameters:

cache -

Returns:

checkCaches

public void checkCaches()

Called from the global major sync event to check if caches can be shrinked. To be shrinked, the size of a cache needs to be larger than the factor defined by MIN_SHRINK_FACTOR and its load needs to be lower than SHRINK_THRESHOLD. If shrinked, the cache will be reset to the default initial cache size.

checkDistribution

public void checkDistribution()

Called from the global minor sync event to check if a smaller cache wants to be resized. If a huge cache is availabe, the method might decide to shrink this cache by a certain amount to make room for the smaller cache to grow.

getDefaultInitialSize

public int getDefaultInitialSize()

Returns the default initial size for all caches.

Returns: