Package com.hazelcast.map

Interface QueryCache<K,V>

Type Parameters:

K - the type of key for this QueryCache

V - the type of value for this QueryCache

public interface QueryCache<K,V>

A concurrent, queryable data structure which is used to cache results of a continuous query executed on an IMap. It can be also thought of as an always up-to-date view or snapshot of the IMap.

Typically, QueryCache is used for performance reasons.

This QueryCache can be configured via QueryCacheConfig.

It can be reached like this:

 

     IMap map = hzInstance.getMap("mapName");
     Predicate predicate = TruePredicate.INSTANCE;
     QueryCache cache = map.getQueryCache(cacheId, predicate, includeValue);

 
 

This cache is evictable. The eviction can be configured with QueryCacheConfig.setEvictionConfig(com.hazelcast.config.EvictionConfig). Events caused by IMap eviction are not reflected to this cache. But the events published after an explicit call to IMap.evict(K) are reflected to this cache.

GOTCHAS

• This QueryCache implementation relies on the eventing system, if a listener is attached to this QueryCache it may receive same event more than once in case of a system failure. Check out tryRecover()
• All writes to this QueryCache is reflected to underlying IMap and that write operation will eventually be reflected to this QueryCache after receiving the event of that operation.
• Currently, updates performed on the entries are reflected in the indexes in a non-atomic way. Therefore, if there are indexes configured for the query cache, their state may slightly lag behind the state of the entries. Use map listeners if you need to observe the state when the entry store and its indexes are consistent about the state of a particular entry, see addEntryListener for more details.
• There are some gotchas same with underlying IMap implementation, one should take care of them before using this QueryCache. Please check gotchas section in IMap class for them.

Since:

3.5

See Also:

• QueryCacheConfig

Method Summary

Modifier and Type	Method	Description
UUID	addEntryListener(MapListener listener, boolean includeValue)
UUID	addEntryListener(MapListener listener, Predicate<K,V> predicate, boolean includeValue)
UUID	addEntryListener(MapListener listener, Predicate<K,V> predicate, K key, boolean includeValue)
UUID	addEntryListener(MapListener listener, K key, boolean includeValue)
void	addIndex(IndexConfig config)
default void	addIndex(IndexType type, String... attributes)
boolean	containsKey(Object key)
boolean	containsValue(Object value)
void	destroy()	Destroys this cache.
Set<Map.Entry<K,V>>	entrySet()
Set<Map.Entry<K,V>>	entrySet(Predicate<K,V> predicate)
V	get(Object key)
Map<K,V>	getAll(Set<K> keys)
String	getName()	Returns the name of this QueryCache.
boolean	isEmpty()
Set<K>	keySet()
Set<K>	keySet(Predicate<K,V> predicate)
boolean	removeEntryListener(UUID id)
int	size()
boolean	tryRecover()	This method can be used to recover from a possible event loss situation.
Collection<V>	values()
Collection<V>	values(Predicate<K,V> predicate)

Method Details

get

V get(Object key)

See Also:

• IMap.get(Object)

containsKey

boolean containsKey(Object key)

See Also:

• IMap.containsKey(Object)

containsValue

boolean containsValue(Object value)

See Also:

• IMap.containsValue(Object)

isEmpty

boolean isEmpty()

See Also:

• Map.isEmpty()

size

int size()

See Also:

• Map.size()

addIndex

default void addIndex(IndexType type,
 String... attributes)

See Also:

• IMap.addIndex(IndexType, String...)

addIndex

void addIndex(IndexConfig config)

See Also:

• IMap.addIndex(IndexConfig)

getAll

Map<K,V> getAll(Set<K> keys)

See Also:

• IMap.getAll(Set)

keySet

Set<K> keySet()

See Also:

• IMap.keySet()

values

Collection<V> values()

See Also:

• IMap.values()

entrySet

Set<Map.Entry<K,V>> entrySet()

See Also:

• IMap.entrySet()

keySet

Set<K> keySet(Predicate<K,V> predicate)

See Also:

• IMap.keySet(Predicate)

values

Collection<V> values(Predicate<K,V> predicate)

See Also:

• IMap.values(Predicate)

entrySet

Set<Map.Entry<K,V>> entrySet(Predicate<K,V> predicate)

See Also:

• IMap.entrySet(Predicate)

addEntryListener

UUID addEntryListener(MapListener listener,
 boolean includeValue)

See Also:

• IMap.addEntryListener(MapListener, boolean)

addEntryListener

UUID addEntryListener(MapListener listener,
 K key,
 boolean includeValue)

See Also:

• IMap.addEntryListener(MapListener, Object, boolean)

addEntryListener

UUID addEntryListener(MapListener listener,
 Predicate<K,V> predicate,
 boolean includeValue)

See Also:

• IMap.addEntryListener(MapListener, Predicate, boolean)

addEntryListener

UUID addEntryListener(MapListener listener,
 Predicate<K,V> predicate,
 K key,
 boolean includeValue)

See Also:

• IMap.addEntryListener(MapListener, Predicate, Object, boolean)

removeEntryListener

boolean removeEntryListener(UUID id)

See Also:

• IMap.removeEntryListener(UUID)

getName

String getName()

Returns the name of this QueryCache. The returned value will never be null.

Returns:

the name of this QueryCache.

tryRecover

boolean tryRecover()

This method can be used to recover from a possible event loss situation. You can detect event loss via EventLostListener

This method tries to make consistent the data in this QueryCache with the data in the underlying IMap by replaying the events after last consistently received ones. As a result of this replaying logic, same event may appear more than once to the QueryCache listeners.

This method returns false if the event is not in the buffer of event publisher side. That means recovery is not possible.

Returns:

true if the QueryCache content will be eventually consistent, otherwise false.

See Also:

• QueryCacheConfig.bufferSize

destroy

void destroy()

Destroys this cache. Clears and releases all local and remote resources created for this cache.