[GitHub] [flink-statefun] tzulitai commented on a change in pull request #105: [FLINK-17533] Add support for multiple concurrent checkpoints

[GitBox <gi...@apache.org>]

tzulitai commented on a change in pull request #105:
URL: https://github.com/apache/flink-statefun/pull/105#discussion_r425636013



##########
File path: statefun-flink/statefun-flink-core/src/main/java/org/apache/flink/statefun/flink/core/feedback/FeedbackUnionOperator.java
##########
@@ -84,14 +90,30 @@ public void processFeedback(T element) {
     if (closedOrDisposed) {
       return;
     }
-    if (isBarrierMessage.test(element)) {
-      feedbackLogger.commit();
+    OptionalLong maybeCheckpoint = isBarrierMessage.apply(element);
+    if (maybeCheckpoint.isPresent()) {
+      commitCheckpoint(maybeCheckpoint.getAsLong());
     } else {
       sendDownstream(element);
-      feedbackLogger.append(element);
+      appendToCheckpoint(element);
+    }
+  }
+
+  private void appendToCheckpoint(T element) {
+    for (UnboundedFeedbackLogger<T> logger : uncompletedCheckpoints.values()) {
+      logger.append(element);
     }
   }
 
+  private void commitCheckpoint(final long checkpointId) {
+    UnboundedFeedbackLogger<T> logger = uncompletedCheckpoints.remove(checkpointId);

Review comment:
       Maybe more of a question from my side:
   Is this method guaranteed to be called for a given checkpoint id, even if the checkpoint already failed?
   I'm wondering if that's a case where this `uncompletedCheckpoints` map grows indefinitely in size.

##########
File path: statefun-flink/statefun-flink-core/src/main/java/org/apache/flink/statefun/flink/core/feedback/Checkpoints.java
##########
@@ -0,0 +1,61 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.flink.statefun.flink.core.feedback;
+
+import java.io.OutputStream;
+import java.util.Objects;
+import java.util.SortedMap;
+import java.util.TreeMap;
+import org.apache.flink.statefun.flink.core.logger.UnboundedFeedbackLogger;
+import org.apache.flink.statefun.flink.core.logger.UnboundedFeedbackLoggerFactory;
+import org.apache.flink.util.IOUtils;
+
+final class Checkpoints<T> implements AutoCloseable {

Review comment:
       Ha 😄You read my mind ahead of time @igalshilman.
   This again addresses my previous nitpick on the new logic introduced in `FeedbackUnionOperator`.
   
   What I think is only missing and nice to have is then a unit test for this `Checkpoints` class 👍 

##########
File path: statefun-flink/statefun-flink-core/src/main/java/org/apache/flink/statefun/flink/core/feedback/FeedbackUnionOperator.java
##########
@@ -105,13 +104,11 @@ private void appendToCheckpoint(T element) {
     }
   }
 
-  private void commitCheckpoint(final long checkpointId) {
-    UnboundedFeedbackLogger<T> logger = uncompletedCheckpoints.remove(checkpointId);
-    checkState(
-        logger != null,
-        "checkpoint barrier for a checkpoint id %d is missing a logger.",
-        checkpointId);
-    logger.commit();
+  private void commitCheckpointUntil(final long checkpointId) {

Review comment:
       Ah :) This answers my previous question already 👍 

##########
File path: statefun-flink/statefun-flink-core/src/main/java/org/apache/flink/statefun/flink/core/feedback/FeedbackUnionOperator.java
##########
@@ -43,20 +48,21 @@
 
   // -- configuration
   private final FeedbackKey<T> feedbackKey;
-  private final SerializablePredicate<T> isBarrierMessage;
+  private final SerializableFunction<T, OptionalLong> isBarrierMessage;
   private final SerializableFunction<T, ?> keySelector;
   private final long totalMemoryUsedForFeedbackCheckpointing;
   private final TypeSerializer<T> elementSerializer;
 
   // -- runtime
-  private transient UnboundedFeedbackLogger<T> feedbackLogger;
+  private transient UnboundedFeedbackLoggerFactory<T> feedbackLoggerFactory;
+  private transient Map<Long, UnboundedFeedbackLogger<T>> uncompletedCheckpoints;
   private transient boolean closedOrDisposed;
   private transient MailboxExecutor mailboxExecutor;
   private transient StreamRecord<T> reusable;
 
   FeedbackUnionOperator(

Review comment:
       Perhaps a bit of a nitpick, but with the added functionality to this class, we're now slightly lacking in unit test coverage.
   
   Before having just the `UnboundedFeedbackLoggerTest` is sufficient as it already essentially encapsulates the core logic.
   
   Maybe moving some of the new methods, such as `commitCheckpoint(maybeCheckpoint.getAsLong());` / `appendToCheckpoints(element);` and the `uncompletedCheckpoints` map, essentially the logic of bookkeeping multiple loggers, to a separate `UnboundedFeedbackLoggers` class, and have a unit test for that is enough.

##########
File path: statefun-flink/statefun-flink-core/src/main/java/org/apache/flink/statefun/flink/core/feedback/FeedbackUnionOperator.java
##########
@@ -84,14 +90,30 @@ public void processFeedback(T element) {
     if (closedOrDisposed) {
       return;
     }
-    if (isBarrierMessage.test(element)) {
-      feedbackLogger.commit();
+    OptionalLong maybeCheckpoint = isBarrierMessage.apply(element);
+    if (maybeCheckpoint.isPresent()) {
+      commitCheckpoint(maybeCheckpoint.getAsLong());
     } else {
       sendDownstream(element);
-      feedbackLogger.append(element);
+      appendToCheckpoint(element);

Review comment:
       nit: maybe rename to -
   ```suggestion
         appendToCheckpoints(element);
   ```




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