pnowojski commented on a change in pull request #10332:
[FLINK-13905][checkpointing] Separate checkpoint triggering into several
asynchronous stages
URL: https://github.com/apache/flink/pull/10332#discussion_r367393658
##########
File path:
flink-runtime/src/main/java/org/apache/flink/runtime/checkpoint/CheckpointCoordinator.java
##########
@@ -485,76 +481,151 @@ public boolean isShutdown() {
CheckpointProperties props,
@Nullable String externalSavepointLocation,
boolean isPeriodic,
- boolean advanceToEndOfTime) throws CheckpointException {
+ boolean advanceToEndOfTime) {
if (advanceToEndOfTime && !(props.isSynchronous() &&
props.isSavepoint())) {
- throw new IllegalArgumentException("Only synchronous
savepoints are allowed to advance the watermark to MAX.");
+ return FutureUtils.completedExceptionally(new
IllegalArgumentException(
+ "Only synchronous savepoints are allowed to
advance the watermark to MAX."));
}
- // make some eager pre-checks
+ final CompletableFuture<CompletedCheckpoint>
onCompletionPromise =
+ new CompletableFuture<>();
synchronized (lock) {
- preCheckBeforeTriggeringCheckpoint(isPeriodic,
props.forceCheckpoint());
- }
-
- // check if all tasks that we need to trigger are running.
- // if not, abort the checkpoint
- Execution[] executions = new Execution[tasksToTrigger.length];
- for (int i = 0; i < tasksToTrigger.length; i++) {
- Execution ee =
tasksToTrigger[i].getCurrentExecutionAttempt();
- if (ee == null) {
- LOG.info("Checkpoint triggering task {} of job
{} is not being executed at the moment. Aborting checkpoint.",
-
tasksToTrigger[i].getTaskNameWithSubtaskIndex(),
- job);
- throw new
CheckpointException(CheckpointFailureReason.NOT_ALL_REQUIRED_TASKS_RUNNING);
- } else if (ee.getState() == ExecutionState.RUNNING) {
- executions[i] = ee;
- } else {
- LOG.info("Checkpoint triggering task {} of job
{} is not in state {} but {} instead. Aborting checkpoint.",
-
tasksToTrigger[i].getTaskNameWithSubtaskIndex(),
- job,
- ExecutionState.RUNNING,
- ee.getState());
- throw new
CheckpointException(CheckpointFailureReason.NOT_ALL_REQUIRED_TASKS_RUNNING);
+ if (isTriggering || !triggerRequestQueue.isEmpty()) {
+ // we can't trigger checkpoint directly if
there is a trigger request being processed
+ // or queued
+ triggerRequestQueue.add(new
CheckpointTriggerRequest(
+ timestamp,
+ props,
+ externalSavepointLocation,
+ isPeriodic,
+ advanceToEndOfTime,
+ onCompletionPromise));
+ return onCompletionPromise;
}
}
+ startTriggeringCheckpoint(
+ timestamp,
+ props,
+ externalSavepointLocation,
+ isPeriodic,
+ advanceToEndOfTime,
+ onCompletionPromise);
+ return onCompletionPromise;
+ }
- // next, check if all tasks that need to acknowledge the
checkpoint are running.
- // if not, abort the checkpoint
- Map<ExecutionAttemptID, ExecutionVertex> ackTasks = new
HashMap<>(tasksToWaitFor.length);
+ private void startTriggeringCheckpoint(
+ long timestamp,
+ CheckpointProperties props,
+ @Nullable String externalSavepointLocation,
+ boolean isPeriodic,
+ boolean advanceToEndOfTime,
+ CompletableFuture<CompletedCheckpoint> onCompletionPromise) {
- for (ExecutionVertex ev : tasksToWaitFor) {
- Execution ee = ev.getCurrentExecutionAttempt();
- if (ee != null) {
- ackTasks.put(ee.getAttemptId(), ev);
- } else {
- LOG.info("Checkpoint acknowledging task {} of
job {} is not being executed at the moment. Aborting checkpoint.",
-
ev.getTaskNameWithSubtaskIndex(),
- job);
- throw new
CheckpointException(CheckpointFailureReason.NOT_ALL_REQUIRED_TASKS_RUNNING);
+ try {
+ // make some eager pre-checks
+ synchronized (lock) {
+ preCheckBeforeTriggeringCheckpoint(isPeriodic,
props.forceCheckpoint());
}
- }
- // we will actually trigger this checkpoint!
+ final Execution[] executions = getTriggerExecutions();
+ final Map<ExecutionAttemptID, ExecutionVertex> ackTasks
= getAckTasks();
+
+ // we will actually trigger this checkpoint!
+ Preconditions.checkState(!isTriggering);
+ isTriggering = true;
+
+ final CompletableFuture<PendingCheckpoint>
pendingCheckpointCompletableFuture =
+ initializeCheckpoint(props,
externalSavepointLocation)
+
.thenApplyAsync((checkpointIdAndStorageLocation) -> createPendingCheckpoint(
+ timestamp,
+ props,
+ ackTasks,
+ isPeriodic,
+
checkpointIdAndStorageLocation.checkpointId,
+
checkpointIdAndStorageLocation.checkpointStorageLocation,
+ onCompletionPromise), timer);
+
+ pendingCheckpointCompletableFuture
+ .thenCompose(this::snapshotMasterState)
+ .whenComplete((ignored, throwable) -> {
+ final PendingCheckpoint checkpoint =
+
FutureUtils.getWithoutException(pendingCheckpointCompletableFuture);
+
+ if (throwable == null && checkpoint !=
null && !checkpoint.isDiscarded()) {
+ // no exception, no discarding,
everything is OK
+ snapshotTaskState(
+ timestamp,
+
checkpoint.getCheckpointId(),
+
checkpoint.getCheckpointStorageLocation(),
+ props,
+ executions,
+ advanceToEndOfTime);
+ onTriggerSuccess();
+ } else {
+ // error handling must be
executed in timer thread
+ timer.execute(() -> {
+ // the initialization
might not be finished yet
+ if (checkpoint == null)
{
+
onTriggerFailure(onCompletionPromise, throwable);
+ } else {
+
onTriggerFailure(checkpoint, throwable);
+ }
+ });
+ }
+ });
Review comment:
I'm a bit confused which thread is actually being used to execute what here.
For example isn't the whole `whenComplete` executed already in the `timer`
thread, since `CheckpointCoordinator#snapshotMasterState` returns a future that
will be completed from the `timer` thread?
If so, why do we need to call `timer.execute(()`?
Regardless if I'm wrong/right about what's executed in which thread, I think
this my confusion shows something has to be changed here. Maybe always
explicitly use the `executor`, `timer` parameter when scheduling/chaining
something, so that the executor is clearly visible? `thenCompose(...)` ->
`thenComposeAsync(..., timer/executor)`? I think that would be especially
helpful as it's not easily visible/understandable what's returned from
`this::snapshotMasterState`. Or at least add comments? But `selfDocumentingCode
> comments`.
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