guozhangwang commented on a change in pull request #8964:
URL: https://github.com/apache/kafka/pull/8964#discussion_r448093846
##########
File path:
streams/src/main/java/org/apache/kafka/streams/processor/internals/StateManagerUtil.java
##########
@@ -38,13 +41,39 @@
*/
final class StateManagerUtil {
static final String CHECKPOINT_FILE_NAME = ".checkpoint";
+ static final long OFFSET_DELTA_THRESHOLD_FOR_CHECKPOINT = 10_000L;
private StateManagerUtil() {}
static RecordConverter converterForStore(final StateStore store) {
return isTimestamped(store) ? rawValueToTimestampedValue() :
identity();
}
+ static boolean checkpointNeeded(final boolean enforceCheckpoint,
+ final Map<TopicPartition, Long>
oldOffsetSnapshot,
+ final Map<TopicPartition, Long>
newOffsetSnapshot) {
+ // we should always have the old snapshot post completing the register
state stores;
+ // if it is null it means the registration is not done and hence we
should not overwrite the checkpoint
+ if (oldOffsetSnapshot == null)
+ return false;
+
+ // if the previous snapshot is empty while the current snapshot is not
then we should always checkpoint;
+ // note if the task is stateless or stateful but no stores logged, the
snapshot would also be empty
+ // and hence it's okay to not checkpoint
+ if (oldOffsetSnapshot.isEmpty() && !newOffsetSnapshot.isEmpty())
+ return true;
+
+ // we can checkpoint if the the difference between the current and the
previous snapshot is large enough
+ long totalOffsetDelta = 0L;
+ for (final Map.Entry<TopicPartition, Long> entry :
newOffsetSnapshot.entrySet()) {
+ totalOffsetDelta +=
Math.abs(oldOffsetSnapshot.getOrDefault(entry.getKey(), 0L) - entry.getValue());
+ }
+
+ // when enforcing checkpoint is required, we should overwrite the
checkpoint if it is different from the old one;
+ // otherwise, we only overwrite the checkpoint if it is largely
different from the old one
+ return enforceCheckpoint ? totalOffsetDelta > 0 : totalOffsetDelta >
OFFSET_DELTA_THRESHOLD_FOR_CHECKPOINT;
Review comment:
I'm a bit torn about this optimization to avoid double checkpointing,
because on the other hand, even if we have not made any progress since loaded
the checkpoint, we'd still need to make a checkpoint upon closing if we have
never made one before -- and I use emptyMap as an indicator for that.
Given that upon suspending we are now less likely to checkpoint, the chance
that we would double checkpointing (when transiting to suspended, and when
transiting to closed) is smaller, and hence I'm thinking maybe I'd just remove
this optimization to make the logic a bit simpler. LMK WDYT.
##########
File path:
streams/src/main/java/org/apache/kafka/streams/processor/internals/StreamTask.java
##########
@@ -542,13 +530,22 @@ public void closeCleanAndRecycleState() {
log.info("Closed clean and recycled state");
}
- private void writeCheckpoint() {
+ /**
+ * The following exceptions maybe thrown from the state manager flushing
call
+ *
+ * @throws TaskMigratedException recoverable error sending changelog
records that would cause the task to be removed
+ * @throws StreamsException fatal error when flushing the state store, for
example sending changelog records failed
+ * or flushing state store get IO errors; such
error should cause the thread to die
+ */
+ @Override
+ protected void maybeWriteCheckpoint(final boolean enforceCheckpoint) {
Review comment:
I decided to extract out the update of the changelog offsets from
actually writing the offsets since even if we do not want to write the file, we
still need to update the offsets.
The reason I did not yet remove the parameter from `checkpoint` is that
global-task is still using it. I plan to remove it when consolidating the
global task.
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