[common] Fix BinaryRowSerializer reuse buffer never shrinking

paimon-common/src/main/java/org/apache/paimon/data/RowHelper.java

@@ -40,15 +40,15 @@ public class RowHelper implements Serializable {
      * Maximum retained reuse buffer size in bytes. Buffers exceeding this cap are eligible for
      * release when the shrink ratio condition is also met.
      */
-    private static final int MAX_RETAINED_REUSE_BUFFER_SIZE = 4 * 1024 * 1024; // 4MB
+    public static final int MAX_RETAINED_REUSE_BUFFER_SIZE = 4 * 1024 * 1024; // 4MB
 
     /**
      * Shrink ratio for hysteresis. The buffer is released only when its capacity exceeds {@link
      * #MAX_RETAINED_REUSE_BUFFER_SIZE} AND is more than {@code SHRINK_RATIO} times the current
      * row's size. This avoids thrashing for sustained medium-to-large records while still releasing
      * after a spike (e.g. 100MB buffer with 5MB rows → 20x > 4x → release).
      */
-    private static final int SHRINK_RATIO = 4;
+    public static final int SHRINK_RATIO = 4;
 
     private final FieldGetter[] fieldGetters;
     private final ValueSetter[] valueSetters;

paimon-common/src/main/java/org/apache/paimon/data/serializer/BinaryRowSerializer.java

@@ -21,6 +21,7 @@
 import org.apache.paimon.data.AbstractPagedInputView;
 import org.apache.paimon.data.AbstractPagedOutputView;
 import org.apache.paimon.data.BinaryRow;
+import org.apache.paimon.data.RowHelper;
 import org.apache.paimon.io.DataInputView;
 import org.apache.paimon.io.DataOutputView;
 import org.apache.paimon.memory.MemorySegment;
@@ -88,6 +89,10 @@ public BinaryRow deserialize(BinaryRow reuse, DataInputView source) throws IOExc
 
         int length = source.readInt();
         if (segments == null || segments[0].size() < length) {
+            // Need a larger buffer
+            segments = new MemorySegment[] {MemorySegment.wrap(new byte[length])};
+        } else if (segments[0].size() > RowHelper.MAX_RETAINED_REUSE_BUFFER_SIZE
+                && segments[0].size() > (long) length * RowHelper.SHRINK_RATIO) {
             segments = new MemorySegment[] {MemorySegment.wrap(new byte[length])};
         }
         source.readFully(segments[0].getArray(), 0, length);

paimon-common/src/test/java/org/apache/paimon/data/serializer/BinaryRowSerializerShrinkTest.java

@@ -0,0 +1,168 @@
+/*
+ * 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.paimon.data.serializer;
+
+import org.apache.paimon.data.BinaryRow;
+import org.apache.paimon.data.BinaryRowWriter;
+import org.apache.paimon.data.BinaryString;
+import org.apache.paimon.io.DataInputDeserializer;
+import org.apache.paimon.io.DataOutputSerializer;
+
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Tests for {@link BinaryRowSerializer#deserialize(BinaryRow, org.apache.paimon.io.DataInputView)},
+ * focusing on the combined cap + ratio shrink behavior.
+ */
+class BinaryRowSerializerShrinkTest {
+
+    private static final int MAX_RETAINED = 4 * 1024 * 1024; // 4MB
+
+    @Test
+    void testShrinksWhenSpikeFollowedBySmallRecord() throws Exception {
+        BinaryRowSerializer serializer = new BinaryRowSerializer(1);
+
+        // Inflate buffer with a large record (> 4MB)
+        BinaryRow largeRow = createRowWithPayload(5 * 1024 * 1024);
+        byte[] largeBytes = serializeRow(serializer, largeRow);
+
+        BinaryRow reuse = serializer.createInstance();
+        reuse = serializer.deserialize(reuse, new DataInputDeserializer(largeBytes));
+        int largeBufferSize = reuse.getSegments()[0].size();
+        assertThat(largeBufferSize).isGreaterThanOrEqualTo(5 * 1024 * 1024);
+
+        // Deserialize a small record — buffer > 4MB and ratio huge > 4x → shrink
+        BinaryRow smallRow = createRowWithPayload(100);
+        byte[] smallBytes = serializeRow(serializer, smallRow);
+        reuse = serializer.deserialize(reuse, new DataInputDeserializer(smallBytes));
+        assertThat(reuse.getSegments()[0].size()).isLessThan(MAX_RETAINED);
+    }
+
+    @Test
+    void testShrinksWhenSpikeFollowedByMediumRecord() throws Exception {
+        BinaryRowSerializer serializer = new BinaryRowSerializer(1);
+
+        // Inflate buffer with a very large record (100MB)
+        BinaryRow hugeRow = createRowWithPayload(100 * 1024 * 1024);
+        byte[] hugeBytes = serializeRow(serializer, hugeRow);
+
+        BinaryRow reuse = serializer.createInstance();
+        reuse = serializer.deserialize(reuse, new DataInputDeserializer(hugeBytes));
+        int hugeBufferSize = reuse.getSegments()[0].size();
+        assertThat(hugeBufferSize).isGreaterThanOrEqualTo(100 * 1024 * 1024);
+
+        // Deserialize a 5MB record — buffer ~100MB, ratio ~20x > 4x → shrink
+        BinaryRow mediumRow = createRowWithPayload(5 * 1024 * 1024);
+        byte[] mediumBytes = serializeRow(serializer, mediumRow);
+        reuse = serializer.deserialize(reuse, new DataInputDeserializer(mediumBytes));
+        assertThat(reuse.getSegments()[0].size()).isLessThan(hugeBufferSize);
+    }
+
+    @Test
+    void testRetainsWhenBufferProportionalToRecordSize() throws Exception {
+        BinaryRowSerializer serializer = new BinaryRowSerializer(1);
+
+        // Inflate buffer with a 5MB record
+        BinaryRow row1 = createRowWithPayload(5 * 1024 * 1024);
+        byte[] bytes1 = serializeRow(serializer, row1);
+
+        BinaryRow reuse = serializer.createInstance();
+        reuse = serializer.deserialize(reuse, new DataInputDeserializer(bytes1));
+        int bufferAfterFirst = reuse.getSegments()[0].size();
+        assertThat(bufferAfterFirst).isGreaterThan(MAX_RETAINED);
+
+        // Deserialize another record just above threshold — ratio ~1.2x < 4x → retain
+        BinaryRow row2 = createRowWithPayload(MAX_RETAINED + 100);
+        byte[] bytes2 = serializeRow(serializer, row2);
+        reuse = serializer.deserialize(reuse, new DataInputDeserializer(bytes2));
+        assertThat(reuse.getSegments()[0].size()).isEqualTo(bufferAfterFirst);
+    }
+
+    @Test
+    void testKeepsSmallBuffer() throws Exception {
+        BinaryRowSerializer serializer = new BinaryRowSerializer(1);
+
+        BinaryRow row1 = createRowWithPayload(1024);
+        byte[] bytes1 = serializeRow(serializer, row1);
+
+        BinaryRow reuse = serializer.createInstance();
+        reuse = serializer.deserialize(reuse, new DataInputDeserializer(bytes1));
+        int bufferSize1 = reuse.getSegments()[0].size();
+
+        // Smaller record — buffer < 4MB, should reuse without shrinking
+        BinaryRow row2 = createRowWithPayload(100);
+        byte[] bytes2 = serializeRow(serializer, row2);
+        reuse = serializer.deserialize(reuse, new DataInputDeserializer(bytes2));
+        assertThat(reuse.getSegments()[0].size()).isEqualTo(bufferSize1);
+    }
+
+    @Test
+    void testGrowsBufferWhenNeeded() throws Exception {
+        BinaryRowSerializer serializer = new BinaryRowSerializer(1);
+
+        BinaryRow smallRow = createRowWithPayload(100);
+        byte[] smallBytes = serializeRow(serializer, smallRow);
+
+        BinaryRow reuse = serializer.createInstance();
+        reuse = serializer.deserialize(reuse, new DataInputDeserializer(smallBytes));
+
+        // Larger record arrives — buffer must grow
+        BinaryRow largerRow = createRowWithPayload(2048);
+        byte[] largerBytes = serializeRow(serializer, largerRow);
+        reuse = serializer.deserialize(reuse, new DataInputDeserializer(largerBytes));
+        assertThat(reuse.getSegments()[0].size()).isGreaterThanOrEqualTo(2048);
+    }
+
+    @Test
+    void testRetainsBufferForConsecutiveLargeRecords() throws Exception {
+        BinaryRowSerializer serializer = new BinaryRowSerializer(1);
+
+        // Inflate buffer with 5MB record
+        BinaryRow largeRow1 = createRowWithPayload(5 * 1024 * 1024);
+        byte[] largeBytes1 = serializeRow(serializer, largeRow1);
+
+        BinaryRow reuse = serializer.createInstance();
+        reuse = serializer.deserialize(reuse, new DataInputDeserializer(largeBytes1));
+        int bufferAfterFirst = reuse.getSegments()[0].size();
+
+        // Another 5MB record — ratio ~1x < 4x → retain
+        BinaryRow largeRow2 = createRowWithPayload(5 * 1024 * 1024);
+        byte[] largeBytes2 = serializeRow(serializer, largeRow2);
+        reuse = serializer.deserialize(reuse, new DataInputDeserializer(largeBytes2));
+        assertThat(reuse.getSegments()[0].size()).isEqualTo(bufferAfterFirst);
+    }
+
+    private static BinaryRow createRowWithPayload(int payloadSize) {
+        BinaryRow row = new BinaryRow(1);
+        BinaryRowWriter writer = new BinaryRowWriter(row, payloadSize + 32);
+        byte[] payload = new byte[payloadSize];
+        writer.writeString(0, BinaryString.fromBytes(payload));
+        writer.complete();
+        return row;
+    }
+
+    private static byte[] serializeRow(BinaryRowSerializer serializer, BinaryRow row)
+            throws Exception {
+        DataOutputSerializer output = new DataOutputSerializer(row.getSizeInBytes() + 4);
+        serializer.serialize(row, output);
+        return output.getCopyOfBuffer();
+    }
+}