聊聊flink的Async I/O
2019-01-19 本文已影响33人
go4it
序
本文主要研究一下flink的Async I/O
实例
// This example implements the asynchronous request and callback with Futures that have the
// interface of Java 8's futures (which is the same one followed by Flink's Future)
/**
* An implementation of the 'AsyncFunction' that sends requests and sets the callback.
*/
class AsyncDatabaseRequest extends RichAsyncFunction<String, Tuple2<String, String>> {
/** The database specific client that can issue concurrent requests with callbacks */
private transient DatabaseClient client;
@Override
public void open(Configuration parameters) throws Exception {
client = new DatabaseClient(host, post, credentials);
}
@Override
public void close() throws Exception {
client.close();
}
@Override
public void asyncInvoke(String key, final ResultFuture<Tuple2<String, String>> resultFuture) throws Exception {
// issue the asynchronous request, receive a future for result
final Future<String> result = client.query(key);
// set the callback to be executed once the request by the client is complete
// the callback simply forwards the result to the result future
CompletableFuture.supplyAsync(new Supplier<String>() {
@Override
public String get() {
try {
return result.get();
} catch (InterruptedException | ExecutionException e) {
// Normally handled explicitly.
return null;
}
}
}).thenAccept( (String dbResult) -> {
resultFuture.complete(Collections.singleton(new Tuple2<>(key, dbResult)));
});
}
}
// create the original stream
DataStream<String> stream = ...;
// apply the async I/O transformation
DataStream<Tuple2<String, String>> resultStream =
AsyncDataStream.unorderedWait(stream, new AsyncDatabaseRequest(), 1000, TimeUnit.MILLISECONDS, 100);
- 本实例展示了flink Async I/O的基本用法，首先是实现AsyncFunction接口，用于编写异步请求逻辑及将结果或异常设置到resultFuture，然后就是使用AsyncDataStream的unorderedWait或orderedWait方法将AsyncFunction作用到DataStream作为transformation；AsyncDataStream的unorderedWait或orderedWait有两个关于async operation的参数，一个是timeout参数用于设置async的超时时间，一个是capacity参数用于指定同一时刻最大允许多少个(
并发)async request在执行
AsyncFunction
flink-streaming-java_2.11-1.7.0-sources.jar!/org/apache/flink/streaming/api/functions/async/AsyncFunction.java
/**
* A function to trigger Async I/O operation.
*
* <p>For each #asyncInvoke, an async io operation can be triggered, and once it has been done,
* the result can be collected by calling {@link ResultFuture#complete}. For each async
* operation, its context is stored in the operator immediately after invoking
* #asyncInvoke, avoiding blocking for each stream input as long as the internal buffer is not full.
*
* <p>{@link ResultFuture} can be passed into callbacks or futures to collect the result data.
* An error can also be propagate to the async IO operator by
* {@link ResultFuture#completeExceptionally(Throwable)}.
*
* <p>Callback example usage:
*
* <pre>{@code
* public class HBaseAsyncFunc implements AsyncFunction<String, String> {
*
* public void asyncInvoke(String row, ResultFuture<String> result) throws Exception {
* HBaseCallback cb = new HBaseCallback(result);
* Get get = new Get(Bytes.toBytes(row));
* hbase.asyncGet(get, cb);
* }
* }
* }</pre>
*
* <p>Future example usage:
*
* <pre>{@code
* public class HBaseAsyncFunc implements AsyncFunction<String, String> {
*
* public void asyncInvoke(String row, final ResultFuture<String> result) throws Exception {
* Get get = new Get(Bytes.toBytes(row));
* ListenableFuture<Result> future = hbase.asyncGet(get);
* Futures.addCallback(future, new FutureCallback<Result>() {
* public void onSuccess(Result result) {
* List<String> ret = process(result);
* result.complete(ret);
* }
* public void onFailure(Throwable thrown) {
* result.completeExceptionally(thrown);
* }
* });
* }
* }
* }</pre>
*
* @param <IN> The type of the input elements.
* @param <OUT> The type of the returned elements.
*/
@PublicEvolving
public interface AsyncFunction<IN, OUT> extends Function, Serializable {
/**
* Trigger async operation for each stream input.
*
* @param input element coming from an upstream task
* @param resultFuture to be completed with the result data
* @exception Exception in case of a user code error. An exception will make the task fail and
* trigger fail-over process.
*/
void asyncInvoke(IN input, ResultFuture<OUT> resultFuture) throws Exception;
/**
* {@link AsyncFunction#asyncInvoke} timeout occurred.
* By default, the result future is exceptionally completed with a timeout exception.
*
* @param input element coming from an upstream task
* @param resultFuture to be completed with the result data
*/
default void timeout(IN input, ResultFuture<OUT> resultFuture) throws Exception {
resultFuture.completeExceptionally(
new TimeoutException("Async function call has timed out."));
}
}
- AsyncFunction接口继承了Function，它定义了asyncInvoke方法以及一个default的timeout方法；asyncInvoke方法执行异步逻辑，然后通过ResultFuture.complete将结果设置到ResultFuture，如果异常则通过ResultFuture.completeExceptionally(Throwable)来传递到ResultFuture
RichAsyncFunction
flink-streaming-java_2.11-1.7.0-sources.jar!/org/apache/flink/streaming/api/functions/async/RichAsyncFunction.java
@PublicEvolving
public abstract class RichAsyncFunction<IN, OUT> extends AbstractRichFunction implements AsyncFunction<IN, OUT> {
private static final long serialVersionUID = 3858030061138121840L;
@Override
public void setRuntimeContext(RuntimeContext runtimeContext) {
Preconditions.checkNotNull(runtimeContext);
if (runtimeContext instanceof IterationRuntimeContext) {
super.setRuntimeContext(
new RichAsyncFunctionIterationRuntimeContext(
(IterationRuntimeContext) runtimeContext));
} else {
super.setRuntimeContext(new RichAsyncFunctionRuntimeContext(runtimeContext));
}
}
@Override
public abstract void asyncInvoke(IN input, ResultFuture<OUT> resultFuture) throws Exception;
//......
}
- RichAsyncFunction继承了AbstractRichFunction，同时声明实现AsyncFunction接口，它不没有实现asyncInvoke，交由子类实现；它覆盖了setRuntimeContext方法，这里使用RichAsyncFunctionRuntimeContext或者RichAsyncFunctionIterationRuntimeContext进行包装
RichAsyncFunctionRuntimeContext
flink-streaming-java_2.11-1.7.0-sources.jar!/org/apache/flink/streaming/api/functions/async/RichAsyncFunction.java
/**
* A wrapper class for async function's {@link RuntimeContext}. The async function runtime
* context only supports basic operations which are thread safe. Consequently, state access,
* accumulators, broadcast variables and the distributed cache are disabled.
*/
private static class RichAsyncFunctionRuntimeContext implements RuntimeContext {
private final RuntimeContext runtimeContext;
RichAsyncFunctionRuntimeContext(RuntimeContext context) {
runtimeContext = Preconditions.checkNotNull(context);
}
@Override
public String getTaskName() {
return runtimeContext.getTaskName();
}
@Override
public MetricGroup getMetricGroup() {
return runtimeContext.getMetricGroup();
}
@Override
public int getNumberOfParallelSubtasks() {
return runtimeContext.getNumberOfParallelSubtasks();
}
@Override
public int getMaxNumberOfParallelSubtasks() {
return runtimeContext.getMaxNumberOfParallelSubtasks();
}
@Override
public int getIndexOfThisSubtask() {
return runtimeContext.getIndexOfThisSubtask();
}
@Override
public int getAttemptNumber() {
return runtimeContext.getAttemptNumber();
}
@Override
public String getTaskNameWithSubtasks() {
return runtimeContext.getTaskNameWithSubtasks();
}
@Override
public ExecutionConfig getExecutionConfig() {
return runtimeContext.getExecutionConfig();
}
@Override
public ClassLoader getUserCodeClassLoader() {
return runtimeContext.getUserCodeClassLoader();
}
// -----------------------------------------------------------------------------------
// Unsupported operations
// -----------------------------------------------------------------------------------
@Override
public DistributedCache getDistributedCache() {
throw new UnsupportedOperationException("Distributed cache is not supported in rich async functions.");
}
@Override
public <T> ValueState<T> getState(ValueStateDescriptor<T> stateProperties) {
throw new UnsupportedOperationException("State is not supported in rich async functions.");
}
@Override
public <T> ListState<T> getListState(ListStateDescriptor<T> stateProperties) {
throw new UnsupportedOperationException("State is not supported in rich async functions.");
}
@Override
public <T> ReducingState<T> getReducingState(ReducingStateDescriptor<T> stateProperties) {
throw new UnsupportedOperationException("State is not supported in rich async functions.");
}
@Override
public <IN, ACC, OUT> AggregatingState<IN, OUT> getAggregatingState(AggregatingStateDescriptor<IN, ACC, OUT> stateProperties) {
throw new UnsupportedOperationException("State is not supported in rich async functions.");
}
@Override
public <T, ACC> FoldingState<T, ACC> getFoldingState(FoldingStateDescriptor<T, ACC> stateProperties) {
throw new UnsupportedOperationException("State is not supported in rich async functions.");
}
@Override
public <UK, UV> MapState<UK, UV> getMapState(MapStateDescriptor<UK, UV> stateProperties) {
throw new UnsupportedOperationException("State is not supported in rich async functions.");
}
@Override
public <V, A extends Serializable> void addAccumulator(String name, Accumulator<V, A> accumulator) {
throw new UnsupportedOperationException("Accumulators are not supported in rich async functions.");
}
@Override
public <V, A extends Serializable> Accumulator<V, A> getAccumulator(String name) {
throw new UnsupportedOperationException("Accumulators are not supported in rich async functions.");
}
@Override
public Map<String, Accumulator<?, ?>> getAllAccumulators() {
throw new UnsupportedOperationException("Accumulators are not supported in rich async functions.");
}
@Override
public IntCounter getIntCounter(String name) {
throw new UnsupportedOperationException("Int counters are not supported in rich async functions.");
}
@Override
public LongCounter getLongCounter(String name) {
throw new UnsupportedOperationException("Long counters are not supported in rich async functions.");
}
@Override
public DoubleCounter getDoubleCounter(String name) {
throw new UnsupportedOperationException("Long counters are not supported in rich async functions.");
}
@Override
public Histogram getHistogram(String name) {
throw new UnsupportedOperationException("Histograms are not supported in rich async functions.");
}
@Override
public boolean hasBroadcastVariable(String name) {
throw new UnsupportedOperationException("Broadcast variables are not supported in rich async functions.");
}
@Override
public <RT> List<RT> getBroadcastVariable(String name) {
throw new UnsupportedOperationException("Broadcast variables are not supported in rich async functions.");
}
@Override
public <T, C> C getBroadcastVariableWithInitializer(String name, BroadcastVariableInitializer<T, C> initializer) {
throw new UnsupportedOperationException("Broadcast variables are not supported in rich async functions.");
}
}
- RichAsyncFunctionRuntimeContext实现了RuntimeContext接口，它将一些方法代理给RuntimeContext，其余的Unsupported的方法都覆盖抛出UnsupportedOperationException
RichAsyncFunctionIterationRuntimeContext
flink-streaming-java_2.11-1.7.0-sources.jar!/org/apache/flink/streaming/api/functions/async/RichAsyncFunction.java
private static class RichAsyncFunctionIterationRuntimeContext extends RichAsyncFunctionRuntimeContext implements IterationRuntimeContext {
private final IterationRuntimeContext iterationRuntimeContext;
RichAsyncFunctionIterationRuntimeContext(IterationRuntimeContext iterationRuntimeContext) {
super(iterationRuntimeContext);
this.iterationRuntimeContext = Preconditions.checkNotNull(iterationRuntimeContext);
}
@Override
public int getSuperstepNumber() {
return iterationRuntimeContext.getSuperstepNumber();
}
// -----------------------------------------------------------------------------------
// Unsupported operations
// -----------------------------------------------------------------------------------
@Override
public <T extends Aggregator<?>> T getIterationAggregator(String name) {
throw new UnsupportedOperationException("Iteration aggregators are not supported in rich async functions.");
}
@Override
public <T extends Value> T getPreviousIterationAggregate(String name) {
throw new UnsupportedOperationException("Iteration aggregators are not supported in rich async functions.");
}
}
- RichAsyncFunctionIterationRuntimeContext继承了RichAsyncFunctionRuntimeContext，实现了IterationRuntimeContext接口，它将getSuperstepNumber方法交由IterationRuntimeContext处理，然后覆盖getIterationAggregator、getPreviousIterationAggregate方法抛出UnsupportedOperationException
AsyncDataStream
flink-streaming-java_2.11-1.7.0-sources.jar!/org/apache/flink/streaming/api/datastream/AsyncDataStream.java
@PublicEvolving
public class AsyncDataStream {
/**
* Output mode for asynchronous operations.
*/
public enum OutputMode { ORDERED, UNORDERED }
private static final int DEFAULT_QUEUE_CAPACITY = 100;
private static <IN, OUT> SingleOutputStreamOperator<OUT> addOperator(
DataStream<IN> in,
AsyncFunction<IN, OUT> func,
long timeout,
int bufSize,
OutputMode mode) {
TypeInformation<OUT> outTypeInfo = TypeExtractor.getUnaryOperatorReturnType(
func,
AsyncFunction.class,
0,
1,
new int[]{1, 0},
in.getType(),
Utils.getCallLocationName(),
true);
// create transform
AsyncWaitOperator<IN, OUT> operator = new AsyncWaitOperator<>(
in.getExecutionEnvironment().clean(func),
timeout,
bufSize,
mode);
return in.transform("async wait operator", outTypeInfo, operator);
}
public static <IN, OUT> SingleOutputStreamOperator<OUT> unorderedWait(
DataStream<IN> in,
AsyncFunction<IN, OUT> func,
long timeout,
TimeUnit timeUnit,
int capacity) {
return addOperator(in, func, timeUnit.toMillis(timeout), capacity, OutputMode.UNORDERED);
}
public static <IN, OUT> SingleOutputStreamOperator<OUT> unorderedWait(
DataStream<IN> in,
AsyncFunction<IN, OUT> func,
long timeout,
TimeUnit timeUnit) {
return addOperator(
in,
func,
timeUnit.toMillis(timeout),
DEFAULT_QUEUE_CAPACITY,
OutputMode.UNORDERED);
}
public static <IN, OUT> SingleOutputStreamOperator<OUT> orderedWait(
DataStream<IN> in,
AsyncFunction<IN, OUT> func,
long timeout,
TimeUnit timeUnit,
int capacity) {
return addOperator(in, func, timeUnit.toMillis(timeout), capacity, OutputMode.ORDERED);
}
public static <IN, OUT> SingleOutputStreamOperator<OUT> orderedWait(
DataStream<IN> in,
AsyncFunction<IN, OUT> func,
long timeout,
TimeUnit timeUnit) {
return addOperator(
in,
func,
timeUnit.toMillis(timeout),
DEFAULT_QUEUE_CAPACITY,
OutputMode.ORDERED);
}
}
- AsyncDataStream提供了unorderedWait、orderedWait两类方法来将AsyncFunction作用于DataStream
- unorderedWait、orderedWait方法有带capacity参数的也有不带capacity参数的，不带capacity参数即默认使用DEFAULT_QUEUE_CAPACITY，即100；这些方法最后都是调用addOperator私有方法来实现，它使用的是AsyncWaitOperator；unorderedWait、orderedWait方法都带了timeout参数，用于指定等待async操作完成的超时时间
- AsyncDataStream提供了两种OutputMode，其中UNORDERED是无序的，即一旦async操作完成就emit结果，当使用TimeCharacteristic.ProcessingTime的时候这种模式延迟最低、负载最低；ORDERED是有序的，即按element的输入顺序emit结果，为了保证有序operator需要缓冲数据，因而会造成一定的延迟及负载
小结
- flink给外部数据访问提供了Asynchronous I/O的API，用于提升streaming的吞吐量，其基本使用就是定义一个实现AsyncFunction接口的function，然后使用AsyncDataStream的unorderedWait或orderedWait方法将AsyncFunction作用到DataStream作为transformation
- AsyncFunction接口继承了Function，它定义了asyncInvoke方法以及一个default的timeout方法；asyncInvoke方法执行异步逻辑，然后通过ResultFuture.complete将结果或异常设置到ResultFuture，如果异常则通过ResultFuture.completeExceptionally(Throwable)来传递到ResultFuture；RichAsyncFunction继承了AbstractRichFunction，同时声明实现AsyncFunction接口，它不没有实现asyncInvoke，交由子类实现；它覆盖了setRuntimeContext方法，这里使用RichAsyncFunctionRuntimeContext或者RichAsyncFunctionIterationRuntimeContext进行包装
- AsyncDataStream的unorderedWait或orderedWait有两个关于async operation的参数，一个是timeout参数用于设置async的超时时间，一个是capacity参数用于指定同一时刻最大允许多少个(
并发)async request在执行；AsyncDataStream提供了两种OutputMode，其中UNORDERED是无序的，即一旦async操作完成就emit结果，当使用TimeCharacteristic.ProcessingTime的时候这种模式延迟最低、负载最低；ORDERED是有序的，即按element的输入顺序emit结果，为了保证有序operator需要缓冲数据，因而会造成一定的延迟及负载
