[GitHub] [kafka] ijuma commented on a diff in pull request #13043: KAFKA-14558: Move LastRecord, TxnMetadata, BatchMetadata, ProducerStateEntry, and ProducerAppendInfo to the storage module

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

ijuma commented on code in PR #13043:
URL: https://github.com/apache/kafka/pull/13043#discussion_r1062635407


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storage/src/main/java/org/apache/kafka/server/log/internals/ProducerStateEntry.java:
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@@ -0,0 +1,149 @@
+/*
+ * 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.server.log.internals;
+
+import org.apache.kafka.common.record.RecordBatch;
+
+import java.util.ArrayDeque;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.Deque;
+import java.util.List;
+import java.util.Optional;
+import java.util.OptionalLong;
+import java.util.stream.Stream;
+
+/**
+ * This class represents the state of a specific producer-id.
+ * It contains batchMetadata queue which is ordered such that the batch with the lowest sequence is at the head of the
+ * queue while the batch with the highest sequence is at the tail of the queue. We will retain at most {@link ProducerStateEntry#NUM_BATCHES_TO_RETAIN}
+ * elements in the queue. When the queue is at capacity, we remove the first element to make space for the incoming batch.
+ */
+public class ProducerStateEntry {
+    public static final int NUM_BATCHES_TO_RETAIN = 5;
+    private final long producerId;
+    private final Deque<BatchMetadata> batchMetadata;
+    private short producerEpoch;
+    public int coordinatorEpoch;
+    public long lastTimestamp;
+    public OptionalLong currentTxnFirstOffset;
+
+    public ProducerStateEntry(long producerId) {
+        this(producerId, Collections.emptyList(), RecordBatch.NO_PRODUCER_EPOCH, -1, RecordBatch.NO_TIMESTAMP, OptionalLong.empty());
+    }
+
+    public ProducerStateEntry(long producerId, short producerEpoch, int coordinatorEpoch, long lastTimestamp, OptionalLong currentTxnFirstOffset) {
+        this(producerId, Collections.emptyList(), producerEpoch, coordinatorEpoch, lastTimestamp, currentTxnFirstOffset);
+    }
+
+    public ProducerStateEntry(long producerId, List<BatchMetadata> batchMetadata, short producerEpoch, int coordinatorEpoch, long lastTimestamp, OptionalLong currentTxnFirstOffset) {

Review Comment:
   Looking at the code, I noticed that we never actually pass multiple `BatchMetadata`, we only ever pass one. Given that, maybe this constructor could take a single element instead of `List`.



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