org.apache.flink.api.common.state

Interface KeyedStateStore

All Known Implementing Classes:

DefaultKeyedStateStore, WindowOperator.AbstractPerWindowStateStore, WindowOperator.MergingWindowStateStore, WindowOperator.PerWindowStateStore

@PublicEvolving
public interface KeyedStateStore

This interface contains methods for registering keyed state with a managed store.

Method Summary

Modifier and Type	Method and Description
<IN,ACC,OUT> AggregatingState<IN,OUT>	getAggregatingState(AggregatingStateDescriptor<IN,ACC,OUT> stateProperties) Gets a handle to the system's key/value folding state.
<T> ListState<T>	getListState(ListStateDescriptor<T> stateProperties) Gets a handle to the system's key/value list state.
<UK,UV> MapState<UK,UV>	getMapState(MapStateDescriptor<UK,UV> stateProperties) Gets a handle to the system's key/value map state.
<T> ReducingState<T>	getReducingState(ReducingStateDescriptor<T> stateProperties) Gets a handle to the system's key/value reducing state.
<T> ValueState<T>	getState(ValueStateDescriptor<T> stateProperties) Gets a handle to the system's key/value state.

Method Detail

getState

@PublicEvolving
<T> ValueState<T> getState(ValueStateDescriptor<T> stateProperties)

Gets a handle to the system's key/value state. The key/value state is only accessible if the function is executed on a KeyedStream. On each access, the state exposes the value for the key of the element currently processed by the function. Each function may have multiple partitioned states, addressed with different names.

Because the scope of each value is the key of the currently processed element, and the elements are distributed by the Flink runtime, the system can transparently scale out and redistribute the state and KeyedStream.

The following code example shows how to implement a continuous counter that counts how many times elements of a certain key occur, and emits an updated count for that element on each occurrence.

 DataStream<MyType> stream = ...;
 KeyedStream<MyType> keyedStream = stream.keyBy("id");

 keyedStream.map(new RichMapFunction<MyType, Tuple2<MyType, Long>>() {

     private ValueState<Long> state;

     public void open(Configuration cfg) {
         state = getRuntimeContext().getState(
                 new ValueStateDescriptor<Long>("count", LongSerializer.INSTANCE, 0L));
     }

     public Tuple2<MyType, Long> map(MyType value) {
         long count = state.value() + 1;
         state.update(count);
         return new Tuple2<>(value, count);
     }
 });
 

Type Parameters:

T - The type of value stored in the state.

Parameters:

stateProperties - The descriptor defining the properties of the stats.

Returns:

The partitioned state object.

Throws:

UnsupportedOperationException - Thrown, if no partitioned state is available for the function (function is not part of a KeyedStream).

getListState

@PublicEvolving
<T> ListState<T> getListState(ListStateDescriptor<T> stateProperties)

Gets a handle to the system's key/value list state. This state is similar to the state accessed via getState(ValueStateDescriptor), but is optimized for state that holds lists. One can adds elements to the list, or retrieve the list as a whole.

This state is only accessible if the function is executed on a KeyedStream.

 DataStream<MyType> stream = ...;
 KeyedStream<MyType> keyedStream = stream.keyBy("id");

 keyedStream.map(new RichFlatMapFunction<MyType, List<MyType>>() {

     private ListState<MyType> state;

     public void open(Configuration cfg) {
         state = getRuntimeContext().getListState(
                 new ListStateDescriptor<>("myState", MyType.class));
     }

     public void flatMap(MyType value, Collector<MyType> out) {
         if (value.isDivider()) {
             for (MyType t : state.get()) {
                 out.collect(t);
             }
         } else {
             state.add(value);
         }
     }
 });
 

Type Parameters:

T - The type of value stored in the state.

Parameters:

stateProperties - The descriptor defining the properties of the stats.

Returns:

The partitioned state object.

Throws:

UnsupportedOperationException - Thrown, if no partitioned state is available for the function (function is not part os a KeyedStream).

getReducingState

@PublicEvolving
<T> ReducingState<T> getReducingState(ReducingStateDescriptor<T> stateProperties)

Gets a handle to the system's key/value reducing state. This state is similar to the state accessed via getState(ValueStateDescriptor), but is optimized for state that aggregates values.

This state is only accessible if the function is executed on a KeyedStream.

 DataStream<MyType> stream = ...;
 KeyedStream<MyType> keyedStream = stream.keyBy("id");

 keyedStream.map(new RichMapFunction<MyType, List<MyType>>() {

     private ReducingState<Long> state;

     public void open(Configuration cfg) {
         state = getRuntimeContext().getReducingState(
                 new ReducingStateDescriptor<>("sum", (a, b) -> a + b, Long.class));
     }

     public Tuple2<MyType, Long> map(MyType value) {
         state.add(value.count());
         return new Tuple2<>(value, state.get());
     }
 });

 

Type Parameters:

T - The type of value stored in the state.

Parameters:

stateProperties - The descriptor defining the properties of the stats.

Returns:

The partitioned state object.

Throws:

UnsupportedOperationException - Thrown, if no partitioned state is available for the function (function is not part of a KeyedStream).

getAggregatingState

@PublicEvolving
<IN,ACC,OUT> AggregatingState<IN,OUT> getAggregatingState(AggregatingStateDescriptor<IN,ACC,OUT> stateProperties)

Gets a handle to the system's key/value folding state. This state is similar to the state accessed via getState(ValueStateDescriptor), but is optimized for state that aggregates values with different types.

This state is only accessible if the function is executed on a KeyedStream.

 DataStream<MyType> stream = ...;
 KeyedStream<MyType> keyedStream = stream.keyBy("id");
 AggregateFunction<...> aggregateFunction = ...

 keyedStream.map(new RichMapFunction<MyType, List<MyType>>() {

     private AggregatingState<MyType, Long> state;

     public void open(Configuration cfg) {
         state = getRuntimeContext().getAggregatingState(
                 new AggregatingStateDescriptor<>("sum", aggregateFunction, Long.class));
     }

     public Tuple2<MyType, Long> map(MyType value) {
         state.add(value);
         return new Tuple2<>(value, state.get());
     }
 });

 

Type Parameters:

IN - The type of the values that are added to the state.

ACC - The type of the accumulator (intermediate aggregation state).

OUT - The type of the values that are returned from the state.

Parameters:

stateProperties - The descriptor defining the properties of the stats.

Returns:

The partitioned state object.

Throws:

UnsupportedOperationException - Thrown, if no partitioned state is available for the function (function is not part of a KeyedStream).

getMapState

@PublicEvolving
<UK,UV> MapState<UK,UV> getMapState(MapStateDescriptor<UK,UV> stateProperties)

Gets a handle to the system's key/value map state. This state is similar to the state accessed via getState(ValueStateDescriptor), but is optimized for state that is composed of user-defined key-value pairs

This state is only accessible if the function is executed on a KeyedStream.

 DataStream<MyType> stream = ...;
 KeyedStream<MyType> keyedStream = stream.keyBy("id");

 keyedStream.map(new RichMapFunction<MyType, List<MyType>>() {

     private MapState<MyType, Long> state;

     public void open(Configuration cfg) {
         state = getRuntimeContext().getMapState(
                 new MapStateDescriptor<>("sum", MyType.class, Long.class));
     }

     public Tuple2<MyType, Long> map(MyType value) {
         return new Tuple2<>(value, state.get(value));
     }
 });

 

Type Parameters:

UK - The type of the user keys stored in the state.

UV - The type of the user values stored in the state.

Parameters:

stateProperties - The descriptor defining the properties of the stats.

Returns:

The partitioned state object.

Throws:

UnsupportedOperationException - Thrown, if no partitioned state is available for the function (function is not part of a KeyedStream).