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https://issues.apache.org/jira/browse/FLINK-3257?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15210328#comment-15210328
]
ASF GitHub Bot commented on FLINK-3257:
---------------------------------------
Github user uce commented on a diff in the pull request:
https://github.com/apache/flink/pull/1668#discussion_r57327419
--- Diff:
flink-streaming-java/src/main/java/org/apache/flink/streaming/runtime/tasks/StreamIterationHead.java
---
@@ -17,43 +17,80 @@
package org.apache.flink.streaming.runtime.tasks;
-import java.util.concurrent.ArrayBlockingQueue;
-import java.util.concurrent.BlockingQueue;
-import java.util.concurrent.TimeUnit;
-
import org.apache.flink.annotation.Internal;
import org.apache.flink.api.common.JobID;
+import org.apache.flink.core.memory.DataInputViewStreamWrapper;
+import org.apache.flink.core.memory.DataOutputViewStreamWrapper;
+import org.apache.flink.runtime.io.network.api.CheckpointBarrier;
+import org.apache.flink.runtime.state.AbstractStateBackend;
+import org.apache.flink.runtime.state.StreamStateHandle;
+import org.apache.flink.streaming.api.operators.AbstractStreamOperator;
+import org.apache.flink.streaming.api.operators.OneInputStreamOperator;
import org.apache.flink.streaming.api.watermark.Watermark;
-import org.apache.flink.streaming.runtime.io.RecordWriterOutput;
import org.apache.flink.streaming.runtime.io.BlockingQueueBroker;
+import org.apache.flink.streaming.runtime.io.RecordWriterOutput;
import org.apache.flink.streaming.runtime.streamrecord.StreamRecord;
+import
org.apache.flink.streaming.runtime.streamrecord.StreamRecordSerializer;
+import org.apache.flink.types.Either;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
+import java.io.InputStream;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.concurrent.ArrayBlockingQueue;
+import java.util.concurrent.BlockingQueue;
+import java.util.concurrent.TimeUnit;
+
@Internal
-public class StreamIterationHead<OUT> extends OneInputStreamTask<OUT, OUT>
{
+public class StreamIterationHead<IN> extends OneInputStreamTask<IN, IN> {
private static final Logger LOG =
LoggerFactory.getLogger(StreamIterationHead.class);
private volatile boolean running = true;
- //
------------------------------------------------------------------------
-
+ /**
+ * A flag that is on during the duration of a checkpoint. While
onSnapshot is true the iteration head has to perform
+ * upstream backup of all records in transit within the loop.
+ */
+ private volatile boolean onSnapshot = false;
--- End diff --
Always accessed in lock scope, no need for `volatile`
> Add Exactly-Once Processing Guarantees in Iterative DataStream Jobs
> -------------------------------------------------------------------
>
> Key: FLINK-3257
> URL: https://issues.apache.org/jira/browse/FLINK-3257
> Project: Flink
> Issue Type: Improvement
> Reporter: Paris Carbone
> Assignee: Paris Carbone
>
> The current snapshotting algorithm cannot support cycles in the execution
> graph. An alternative scheme can potentially include records in-transit
> through the back-edges of a cyclic execution graph (ABS [1]) to achieve the
> same guarantees.
> One straightforward implementation of ABS for cyclic graphs can work as
> follows along the lines:
> 1) Upon triggering a barrier in an IterationHead from the TaskManager start
> block output and start upstream backup of all records forwarded from the
> respective IterationSink.
> 2) The IterationSink should eventually forward the current snapshotting epoch
> barrier to the IterationSource.
> 3) Upon receiving a barrier from the IterationSink, the IterationSource
> should finalize the snapshot, unblock its output and emit all records
> in-transit in FIFO order and continue the usual execution.
> --
> Upon restart the IterationSource should emit all records from the injected
> snapshot first and then continue its usual execution.
> Several optimisations and slight variations can be potentially achieved but
> this can be the initial implementation take.
> [1] http://arxiv.org/abs/1506.08603
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