[GitHub] [kafka] C0urante commented on a change in pull request #11323: KAFKA-12226: Commit source task offsets without blocking on batch delivery

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C0urante commented on a change in pull request #11323:
URL: https://github.com/apache/kafka/pull/11323#discussion_r720382154



##########
File path: connect/runtime/src/main/java/org/apache/kafka/connect/runtime/SubmittedRecords.java
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@@ -0,0 +1,132 @@
+/*
+ * 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.kafka.connect.runtime;
+
+import org.apache.kafka.connect.source.SourceRecord;
+
+import java.util.Deque;
+import java.util.HashMap;
+import java.util.LinkedList;
+import java.util.Map;
+
+/**
+ * Used to track source records that have been (or are about to be) dispatched to a producer and their accompanying
+ * source offsets.
+ * Note that this class is not thread-safe.
+ */
+class SubmittedRecords {
+    private final Map<Map<String, Object>, Deque<SubmittedRecord>> records;
+
+    public SubmittedRecords() {
+        this.records = new HashMap<>();
+    }
+
+    /**
+     * Enqueue a new source record before dispatching it to a producer.
+     * @param record the record about to be dispatched; may not be null but may have a null
+     * {@link SourceRecord#sourcePartition()} and/or {@link SourceRecord#sourceOffset()}
+     * @return a {@link SubmittedRecord} that can be either {@link SubmittedRecord#ack() acknowledged} once ack'd by
+     * the producer, or {@link #remove removed} if synchronously rejected by the producer
+     */
+    @SuppressWarnings("unchecked")
+    public SubmittedRecord submit(SourceRecord record) {
+        return submit((Map<String, Object>) record.sourcePartition(), (Map<String, Object>) record.sourceOffset());
+    }
+
+    // Convenience method for testing
+    SubmittedRecord submit(Map<String, Object> partition, Map<String, Object> offset) {
+        SubmittedRecord result = new SubmittedRecord(partition, offset);
+        records.computeIfAbsent(result.partition(), p -> new LinkedList<>())
+                .add(result);
+        return result;
+    }
+
+    /**
+     * Remove a source record and do not take it into account any longer when tracking offsets.
+     * Useful if the record has been synchronously rejected by the producer.

Review comment:
       That's not actually the case; the use of [`Deque::removeLastOccurrence`](https://docs.oracle.com/javase/8/docs/api/java/util/Deque.html#removeLastOccurrence-java.lang.Object-) is different from [`Deque::removeLast`](https://docs.oracle.com/javase/8/docs/api/java/util/Deque.html#removeLast--) and [`Deque::pollLast`](https://docs.oracle.com/javase/8/docs/api/java/util/Deque.html#pollLast--) in that it can and will remove an element from anywhere in the deque (as opposed to just the element at the very end) if it `equals` the one passed to `removeLastOccurrence`. The reason `removeLastOccurrence` is used here instead of the more-common [`remove`](https://docs.oracle.com/javase/8/docs/api/java/util/Deque.html#remove-java.lang.Object-) is that, at least with the current use of `SubmittedRecords` by the `WorkerSourceTask`, any calls to `SubmittedRecords::remove` will pass in the most-recently-submitted record, which will then be at the deque it was inserted into, so there's a (poten
 tially-substantial) performance gain.
   
   I wonder if it might be helpful to alter this method:
   - By renaming to `removeLastOccurrence`
   - By clarifying in the Javadoc that, if multiple instances of the same `SubmittedRecord` have been submitted already, only the first one found (traversing from the end of the deque backward) will be removed




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