findepi commented on code in PR #10691:
URL: https://github.com/apache/iceberg/pull/10691#discussion_r1686401382
##########
core/src/main/java/org/apache/iceberg/util/ParallelIterable.java:
##########
@@ -136,30 +169,33 @@ private boolean checkTasks() {
}
}
- return !closed && (tasks.hasNext() || hasRunningTask);
+ return !closed.get() && (tasks.hasNext() || hasRunningTask);
}
- private Future<?> submitNextTask() {
- if (!closed && tasks.hasNext()) {
- return workerPool.submit(tasks.next());
+ private CompletableFuture<Optional<Task<T>>> submitNextTask() {
+ if (!closed.get()) {
+ if (!yieldedTasks.isEmpty()) {
+ return CompletableFuture.supplyAsync(yieldedTasks.removeFirst(),
workerPool);
+ } else if (tasks.hasNext()) {
+ return CompletableFuture.supplyAsync(tasks.next(), workerPool);
+ }
}
return null;
}
@Override
public synchronized boolean hasNext() {
- Preconditions.checkState(!closed, "Already closed");
-
- // if the consumer is processing records more slowly than the producers,
then this check will
- // prevent tasks from being submitted. while the producers are running,
this will always
- // return here before running checkTasks. when enough of the tasks are
finished that the
- // consumer catches up, then lots of new tasks will be submitted at
once. this behavior is
- // okay because it ensures that records are not stacking up waiting to
be consumed and taking
- // up memory.
- //
- // consumers that process results quickly will periodically exhaust the
queue and submit new
- // tasks when checkTasks runs. fast consumers should not be delayed.
- if (!queue.isEmpty()) {
+ Preconditions.checkState(!closed.get(), "Already closed");
+
+ // If the consumer is processing records more slowly than the producers,
the producers will
+ // eventually fill the queue and yield, returning continuations.
Continuations and new tasks
+ // are started by checkTasks(). The check here prevents us from
restarting continuations or
+ // starting new tasks too early (when queue is almost full) or too late
(when queue is already
+ // emptied). Restarting too early would lead to tasks yielding very
quickly (CPU waste on
+ // scheduling). Restarting too late would mean the consumer may need to
wait for the tasks
+ // to produce new items. A consumer slower than producers shouldn't need
to wait.
+ int queueLowWaterMark = maxQueueSize / 2;
Review Comment:
re this being class static field -- currently this is instance parameter,
the constant serves only as a default
re this being class non-static (instance) field -- i replied to this in
https://github.com/apache/iceberg/pull/10691#discussion_r1684130747. let me
know what you think about this.
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