XComp commented on code in PR #22010:
URL: https://github.com/apache/flink/pull/22010#discussion_r1257913768
##########
flink-streaming-java/src/main/java/org/apache/flink/streaming/api/functions/source/datagen/SequenceGenerator.java:
##########
@@ -189,8 +206,28 @@ public static SequenceGenerator<String>
stringGenerator(long start, long end) {
return new SequenceGenerator<String>(start, end) {
@Override
public String next() {
- return valuesToEmit.poll().toString();
+ return nextValue().toString();
}
};
}
+
+ /**
+ * The internal state of the sequence generator, which is used to record
the latest state of the
+ * sequence value sent by the current sequence generator. When recovering
from the state, it is
+ * guaranteed to continue sending the sequence value from the latest state.
+ */
+ private static class InternalState implements Comparable<InternalState> {
Review Comment:
What's your opinion on renaming this internal class into `SubTaskState`?
`InternalState` sounds too generic. :thinking:
##########
flink-streaming-java/src/main/java/org/apache/flink/streaming/api/functions/source/datagen/SequenceGenerator.java:
##########
@@ -65,33 +80,45 @@ public void open(
this.checkpointedState == null,
"The " + getClass().getSimpleName() + " has already been
initialized.");
- this.checkpointedState =
- context.getOperatorStateStore()
- .getListState(
- new ListStateDescriptor<>(
- name + "-sequence-state",
LongSerializer.INSTANCE));
- this.valuesToEmit = new ArrayDeque<>();
- if (context.isRestored()) {
- // upon restoring
+ ListStateDescriptor<InternalState> stateDescriptor =
Review Comment:
```suggestion
final ListStateDescriptor<InternalState> stateDescriptor =
```
There are a few other code locations where we could make use of the `final`
keyword for local variables.
##########
flink-streaming-java/src/main/java/org/apache/flink/streaming/api/functions/source/datagen/SequenceGenerator.java:
##########
@@ -22,29 +22,44 @@
import org.apache.flink.api.common.functions.RuntimeContext;
import org.apache.flink.api.common.state.ListState;
import org.apache.flink.api.common.state.ListStateDescriptor;
-import org.apache.flink.api.common.typeutils.base.LongSerializer;
+import org.apache.flink.api.common.typeinfo.TypeInformation;
import org.apache.flink.runtime.state.FunctionInitializationContext;
import org.apache.flink.runtime.state.FunctionSnapshotContext;
import org.apache.flink.util.Preconditions;
+import org.apache.flink.shaded.guava30.com.google.common.collect.Queues;
+
import java.math.BigDecimal;
import java.math.MathContext;
import java.math.RoundingMode;
-import java.util.ArrayDeque;
-import java.util.Deque;
+import java.util.ArrayList;
+import java.util.NoSuchElementException;
+import java.util.Queue;
/**
* A stateful, re-scalable {@link DataGenerator} that emits each number from a
given interval
* exactly once, possibly in parallel.
+ *
+ * <p>It maintains a state internally to record the position of the current
subtask sending
+ * sequence. When the task resumes, it will continue to send the sequence
value according to the
+ * position sent by the state, until all the sequences have been sent.
+ *
+ * <p><b>IMPORTANT NOTE: </b> When the degree of parallelism increases, there
may be cases where
+ * subtasks are running empty. When the degree of parallelism decreases, there
may be cases where
+ * one subtask handles multiple states.
Review Comment:
Shall we also add that decreasing the parallelism might result in an
out-of-orderness of the sequence?
##########
flink-streaming-java/src/main/java/org/apache/flink/streaming/api/functions/source/datagen/SequenceGenerator.java:
##########
@@ -65,33 +80,45 @@ public void open(
this.checkpointedState == null,
"The " + getClass().getSimpleName() + " has already been
initialized.");
- this.checkpointedState =
- context.getOperatorStateStore()
- .getListState(
- new ListStateDescriptor<>(
- name + "-sequence-state",
LongSerializer.INSTANCE));
- this.valuesToEmit = new ArrayDeque<>();
- if (context.isRestored()) {
- // upon restoring
+ ListStateDescriptor<InternalState> stateDescriptor =
+ new ListStateDescriptor<>(
+ name + "-sequence-state",
TypeInformation.of(InternalState.class));
+ this.checkpointedState =
context.getOperatorStateStore().getListState(stateDescriptor);
+ this.internalStates = Queues.newPriorityQueue();
- for (Long v : this.checkpointedState.get()) {
- this.valuesToEmit.add(v);
- }
+ if (context.isRestored()) {
+ checkpointedState.get().forEach(state ->
internalStates.offer(state));
} else {
- // the first time the job is executed
- final int stepSize = runtimeContext.getNumberOfParallelSubtasks();
- final int taskIdx = runtimeContext.getIndexOfThisSubtask();
- final long congruence = start + taskIdx;
-
- long totalNoOfElements = Math.abs(end - start + 1);
- final int baseSize = safeDivide(totalNoOfElements, stepSize);
- final int toCollect =
- (totalNoOfElements % stepSize > taskIdx) ? baseSize + 1 :
baseSize;
-
- for (long collected = 0; collected < toCollect; collected++) {
- this.valuesToEmit.add(collected * stepSize + congruence);
+ // The first time the job is executed.
+ final int startOffset = runtimeContext.getIndexOfThisSubtask();
+ final long stepSize = runtimeContext.getNumberOfParallelSubtasks();
+ InternalState state = new InternalState(stepSize, start +
startOffset);
+ internalStates.offer(state);
+ }
+ }
+
+ public Long nextValue() {
+ if (internalStates.isEmpty()) {
+ // Before calling nextValue method, you should call hasNext to
check.
Review Comment:
```suggestion
```
This comment doesn't add any value, don't you think? :thinking: If you want
to give this hint to the developer, you might want to add it to the error
message. Otherwise, you're expecting the developer to do a code investigation
to find the hint of this comment.
##########
flink-streaming-java/src/main/java/org/apache/flink/streaming/api/functions/source/datagen/SequenceGenerator.java:
##########
@@ -22,29 +22,44 @@
import org.apache.flink.api.common.functions.RuntimeContext;
import org.apache.flink.api.common.state.ListState;
import org.apache.flink.api.common.state.ListStateDescriptor;
-import org.apache.flink.api.common.typeutils.base.LongSerializer;
+import org.apache.flink.api.common.typeinfo.TypeInformation;
import org.apache.flink.runtime.state.FunctionInitializationContext;
import org.apache.flink.runtime.state.FunctionSnapshotContext;
import org.apache.flink.util.Preconditions;
+import org.apache.flink.shaded.guava30.com.google.common.collect.Queues;
Review Comment:
```suggestion
import org.apache.flink.shaded.guava31.com.google.common.collect.Queues;
```
This won't work anymore because the `flink-shaded` dependencies were
upgraded (FLINK-32032). Rebasing the branch might reveal other affected code
locations.
##########
flink-streaming-java/src/main/java/org/apache/flink/streaming/api/functions/source/datagen/SequenceGenerator.java:
##########
@@ -65,33 +80,45 @@ public void open(
this.checkpointedState == null,
"The " + getClass().getSimpleName() + " has already been
initialized.");
- this.checkpointedState =
- context.getOperatorStateStore()
- .getListState(
- new ListStateDescriptor<>(
- name + "-sequence-state",
LongSerializer.INSTANCE));
- this.valuesToEmit = new ArrayDeque<>();
- if (context.isRestored()) {
- // upon restoring
+ ListStateDescriptor<InternalState> stateDescriptor =
+ new ListStateDescriptor<>(
+ name + "-sequence-state",
TypeInformation.of(InternalState.class));
+ this.checkpointedState =
context.getOperatorStateStore().getListState(stateDescriptor);
+ this.internalStates = Queues.newPriorityQueue();
Review Comment:
```suggestion
this.internalStates = Queues.newPriorityQueue();
```
Can't we make `internalStates` a `final` field? We don't need to
re-instantiate it. I'm then wondering whether we could add a Precondition that
checks here that the queue is empty when calling the `open` method or whether
there are situations where the queue could still have entries (in which case we
would have to call `clear()`)?
##########
flink-streaming-java/src/main/java/org/apache/flink/streaming/api/functions/source/datagen/SequenceGenerator.java:
##########
@@ -22,29 +22,44 @@
import org.apache.flink.api.common.functions.RuntimeContext;
import org.apache.flink.api.common.state.ListState;
import org.apache.flink.api.common.state.ListStateDescriptor;
-import org.apache.flink.api.common.typeutils.base.LongSerializer;
+import org.apache.flink.api.common.typeinfo.TypeInformation;
import org.apache.flink.runtime.state.FunctionInitializationContext;
import org.apache.flink.runtime.state.FunctionSnapshotContext;
import org.apache.flink.util.Preconditions;
+import org.apache.flink.shaded.guava30.com.google.common.collect.Queues;
+
import java.math.BigDecimal;
import java.math.MathContext;
import java.math.RoundingMode;
-import java.util.ArrayDeque;
-import java.util.Deque;
+import java.util.ArrayList;
+import java.util.NoSuchElementException;
+import java.util.Queue;
/**
* A stateful, re-scalable {@link DataGenerator} that emits each number from a
given interval
* exactly once, possibly in parallel.
+ *
+ * <p>It maintains a state internally to record the position of the current
subtask sending
+ * sequence. When the task resumes, it will continue to send the sequence
value according to the
+ * position sent by the state, until all the sequences have been sent.
+ *
+ * <p><b>IMPORTANT NOTE: </b> When the degree of parallelism increases, there
may be cases where
+ * subtasks are running empty. When the degree of parallelism decreases, there
may be cases where
+ * one subtask handles multiple states.
*/
@Experimental
public abstract class SequenceGenerator<T> implements DataGenerator<T> {
private final long start;
private final long end;
+ /**
+ * Save the intermediate state of the data to be sent by the current
subtask,when the state
Review Comment:
```suggestion
* Save the intermediate state of the data to be sent by the current
subtask, when the state
```
nit
##########
flink-streaming-java/src/main/java/org/apache/flink/streaming/api/functions/source/datagen/SequenceGenerator.java:
##########
@@ -189,8 +206,28 @@ public static SequenceGenerator<String>
stringGenerator(long start, long end) {
return new SequenceGenerator<String>(start, end) {
@Override
public String next() {
- return valuesToEmit.poll().toString();
+ return nextValue().toString();
}
};
}
+
+ /**
+ * The internal state of the sequence generator, which is used to record
the latest state of the
Review Comment:
```suggestion
* The internal state of the sequence generator's subtask(s), which is
used to record the latest state of the
```
Is this more specific?
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