com.bigdata.cache
Interface IGlobalLRU<K,V>

All Known Subinterfaces:

IHardReferenceGlobalLRU<K,V>

All Known Implementing Classes:

HardReferenceGlobalLRU, HardReferenceGlobalLRURecycler, HardReferenceGlobalLRURecyclerExplicitDeleteRequired, StoreAndAddressLRUCache, WeakReferenceGlobalLRU

public interface IGlobalLRU<K,V>

Factory for per-IRawStore caches backed by a global LRU allowing competition for buffer space across all requests for decompressed records, including B+Tree INodeData and ILeafData objects.

The vast majority of all data in the stores are B+Tree INodeData and ILeafData records. This factory provides per-IRawStore cache instances which can dramatically reduce read IO for B+Trees, and thus for the entire database. This also serves as the "leafCache" for the IndexSegment, which uses linked-leaf navigation for ITupleIterator and ITupleCursors and does not otherwise buffer leaves when performing key range scans (versus top-down navigation).

There is one cache per store. All cache instances are backed by a shared Least Recently Used (LRU) policy. Entries will be evicted from the appropriate cache as they fall of the end of the LRU. A global LRU ensures that all cache instances compete for the same memory resources.

Each per-store cache provides a canonicalizing mapping from the Long address of a record to a WeakReference value. The referent of the WeakReference may be an IDataRecord, INodeData, ILeafData, or other object whose persistent state was coded by (or serialized by) the record having that address.

Note: The individual cache instances for each IRawStore reclaim JVM heap space as the WeakReference values are cleared. The set of such instances is also a ConcurrentWeakValueCache with a backing LRU so we can hold onto the canonicalizing mappings for closed stores which might be reopened.

Note: The global LRU may have impact on GC of the old generation since there will be a tendency of the backing byte[]s to be held long enough to become tenured. Newer incremental garbage collections are designed to address this problem.

Note: While caching compressed records would have a smaller memory footprint, this class provides for caching decompressed records since high-level data structures (such as the B+Trees) do not retain references to the compressed data records. Therefore a compressed data record cache based on weak reference semantics for the compressed ByteBuffers would be of little utility.

Version:

$Id: IGlobalLRU.java 2265 2009-10-26 12:51:06Z thompsonbry $

Author:

Bryan Thompson

TODO:

convert to long? By getting rid of this generic type as can allow native long hash map implementations.

Nested Class Summary

static interface	IGlobalLRU.IGlobalLRUCounters Interface defines some standard counters for the global LRU.
static interface	IGlobalLRU.ILRUCache<K,V> Interface for cache of read-only records from a specific IRawStore backed by a shared LRU.

Method Summary

void	deleteCache(UUID storeUUID) Remove the cache for the IRawStore from the set of caches maintained by this class and clear any entries in that cache.
void	discardAllCaches() Clear all per-IRawStore cache instances.
IGlobalLRU.ILRUCache<K,V>	getCache(UUID storeUUID, IAddressManager am) An canonicalizing factory for cache instances supporting random access to decompressed IDataRecords, higher-level data structures wrapping those decompressed data records (INodeData and ILeafData ), or objects deserialized from those IDataRecords.
CounterSet	getCounterSet() The counters for the global LRU.

Method Detail

getCache

IGlobalLRU.ILRUCache<K,V> getCache(UUID storeUUID,
                                   IAddressManager am)

An canonicalizing factory for cache instances supporting random access to decompressed IDataRecords, higher-level data structures wrapping those decompressed data records (INodeData and ILeafData ), or objects deserialized from those IDataRecords.

Parameters:

storeUUID - The store's UUID.

am - The IAddressManager for that store (optional, but used to compute the bytes on disk for record and hence highly desired).

Returns:

The cache for records in the store.

See Also:

AbstractBTree.readNodeOrLeaf(long), IndexSegmentStore.reopen(), LRUNexus.getCache(IRawStore)

deleteCache

void deleteCache(UUID storeUUID)

Remove the cache for the IRawStore from the set of caches maintained by this class and clear any entries in that cache. This method SHOULD be used when the persistent resources for the store are deleted. It SHOULD NOT be used if a store is simply closed in a context when the store COULD be re-opened. In such cases, the cache for that store will be automatically released after it has become only weakly reachable.

Parameters:

storeUUID - The store's UUID.

See Also:

IRawStore.destroy(), IRawStore.deleteResources()

discardAllCaches

void discardAllCaches()

Clear all per-IRawStore cache instances. This may be used if all bigdata instances in the JVM are closed, but SHOULD NOT be invoked if you are just closing some IRawStore.

getCounterSet

CounterSet getCounterSet()

The counters for the global LRU.