com.sleepycat.je.rep.impl.node

Class DbCache

java.lang.Object

com.sleepycat.je.rep.impl.node.DbCache

public class DbCache
extends Object

Cache used to maintain DatabaseImpl handles. The cache retains some configurable number of MRU entries. In addition, the cache will discard MRU entries that have not been used within a configurable timeout period.

Implementation notes:

• The methods are not synchronized, since it's used exclusively from the single threaded replay thread.
• The timeout mechanism is coarse and is implemented by a lightweight tick mechanism that minimizes calls to the system clock, since we expect the cache to be consulted very frequently and need to minimize the overhead. The tick method should be invoked with a period that's less than the timeout interval if it is to work effectively.

Method Summary

Modifier and Type	Method and Description
void	clear() Clears out the cache releasing db handles as well
DatabaseImpl	get(DatabaseId dbId, Txn txn) Returns the DatabaseImpl associated with the dbId, caching the return value, if it's not already cached.
int	getMaxEntries() Returns the max entries that can be held by the cache.
int	getTimeoutMs() Returns the configured timeout in ms.
void	setConfig(RepConfigManager configMgr) Updates the configuration of the db cache, by resetting maxEntries and timeoutMs to the configured values.
void	tick() The tick() method forms the basis for removing stale entries from the cache.

Methods inherited from class java.lang.Object

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

Method Detail

tick

public void tick()

The tick() method forms the basis for removing stale entries from the cache. It effectively advances the "clock" and removes any entries that have been rendered stale.

get

public DatabaseImpl get(DatabaseId dbId,
                        Txn txn)

Returns the DatabaseImpl associated with the dbId, caching the return value, if it's not already cached. The open triggers will be invoked if this was the first write reference.

Parameters:

dbId - the dbId that is to be resolved.

Returns:

the corresponding DatabaseImpl

setConfig

public void setConfig(RepConfigManager configMgr)

Updates the configuration of the db cache, by resetting maxEntries and timeoutMs to the configured values.

Note that setting the cache to a smaller max entry does not immediately reduce the number of entries currently in the cache, if the size of the cache is already at the maximum. The reduction will take place incrementally over time, as calls to "put" operations are made and DbCacheLinkedHashMap#removeEldestEntry is invoked for each put operation. This incremental cache size reduction is not expected to be a significant drawback in practice.

Parameters:

configMgr - the configuration holding the cache parameters

getMaxEntries

public int getMaxEntries()

Returns the max entries that can be held by the cache.

getTimeoutMs

public int getTimeoutMs()

Returns the configured timeout in ms. If a db handle has been inactive for a period of time that exceeds the timeout it's removed from the cache.

clear

public void clear()

Clears out the cache releasing db handles as well