@PublicEvolving public interface KeyedStateStore
Modifier and Type | Method and Description |
---|---|
<T> ListState<T> |
getListState(ListStateDescriptor<T> stateProperties)
Gets a handle to the system's key/value list state.
|
<T> ReducingState<T> |
getReducingState(ReducingStateDescriptor<T> stateProperties)
Gets a handle to the system's key/value list state.
|
<T> ValueState<T> |
getState(ValueStateDescriptor<T> stateProperties)
Gets a handle to the system's key/value state.
|
@PublicEvolving <T> ValueState<T> getState(ValueStateDescriptor<T> stateProperties)
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> count;
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(value);
return new Tuple2<>(value, count);
}
});
T
- The type of value stored in the state.stateProperties
- The descriptor defining the properties of the stats.UnsupportedOperationException
- Thrown, if no partitioned state is available for the
function (function is not part of a KeyedStream).@PublicEvolving <T> ListState<T> getListState(ListStateDescriptor<T> stateProperties)
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);
}
}
});
T
- The type of value stored in the state.stateProperties
- The descriptor defining the properties of the stats.UnsupportedOperationException
- Thrown, if no partitioned state is available for the
function (function is not part os a KeyedStream).@PublicEvolving <T> ReducingState<T> getReducingState(ReducingStateDescriptor<T> stateProperties)
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> sum;
public void open(Configuration cfg) {
state = getRuntimeContext().getReducingState(
new ReducingStateDescriptor<>("sum", MyType.class, 0L, (a, b) -> a + b));
}
public Tuple2<MyType, Long> map(MyType value) {
sum.add(value.count());
return new Tuple2<>(value, sum.get());
}
});
T
- The type of value stored in the state.stateProperties
- The descriptor defining the properties of the stats.UnsupportedOperationException
- Thrown, if no partitioned state is available for the
function (function is not part of a KeyedStream).Copyright © 2014–2017 The Apache Software Foundation. All rights reserved.