polish

paimon-core/src/main/java/org/apache/paimon/mergetree/compact/LookupChangelogMergeFunctionWrapper.java

@@ -23,8 +23,7 @@
 import org.apache.paimon.data.InternalRow;
 import org.apache.paimon.types.RowKind;
 
-import java.util.Iterator;
-import java.util.LinkedList;
+import java.util.List;
 import java.util.function.Function;
 
 import static org.apache.paimon.utils.Preconditions.checkArgument;
@@ -47,7 +46,6 @@
 public class LookupChangelogMergeFunctionWrapper implements MergeFunctionWrapper<ChangelogResult> {
 
     private final LookupMergeFunction mergeFunction;
-    private final MergeFunction<KeyValue> mergeFunction2;
     private final Function<InternalRow, KeyValue> lookup;
 
     private final ChangelogResult reusedResult = new ChangelogResult();
@@ -67,7 +65,6 @@ public LookupChangelogMergeFunctionWrapper(
                 "Merge function should be a LookupMergeFunction, but is %s, there is a bug.",
                 mergeFunction.getClass().getName());
         this.mergeFunction = (LookupMergeFunction) mergeFunction;
-        this.mergeFunction2 = mergeFunctionFactory.create();
         this.lookup = lookup;
         this.valueEqualiser = valueEqualiser;
         this.changelogRowDeduplicate = changelogRowDeduplicate;
@@ -85,41 +82,19 @@ public void add(KeyValue kv) {
 
     @Override
     public ChangelogResult getResult() {
-        // 1. Compute the latest high level record and containLevel0 of candidates
-        LinkedList<KeyValue> candidates = mergeFunction.candidates();
-        Iterator<KeyValue> descending = candidates.descendingIterator();
-        KeyValue highLevel = null;
-        boolean containLevel0 = false;
-        while (descending.hasNext()) {
-            KeyValue kv = descending.next();
-            if (kv.level() > 0) {
-                descending.remove();
-                if (highLevel == null) {
-                    highLevel = kv;
-                }
-            } else {
-                containLevel0 = true;
-            }
-        }
+        LookupMergeRecordManager recordManager = mergeFunction.recordManager();
+        mergeFunction.reset();
 
-        // 2. Lookup if latest high level record is absent
-        if (highLevel == null) {
-            InternalRow lookupKey = candidates.get(0).key();
-            highLevel = lookup.apply(lookupKey);
-        }
+        // 1. Lookup if latest high level record is absent
+        List<KeyValue> candidates = recordManager.getCandidates(lookup);
 
-        // 3. Calculate result
-        mergeFunction2.reset();
-        if (highLevel != null) {
-            mergeFunction2.add(highLevel);
-        }
-        candidates.forEach(mergeFunction2::add);
-        KeyValue result = mergeFunction2.getResult();
+        // 2. Calculate result
+        KeyValue result = mergeFunction.getResult(candidates);
 
-        // 4. Set changelog when there's level-0 records
+        // 3. Set changelog when there's level-0 records
         reusedResult.reset();
-        if (containLevel0) {
-            setChangelog(highLevel, result);
+        if (recordManager.containsLevel0()) {
+            setChangelog(recordManager.highLevel(), result);
         }
 
         return reusedResult.setResult(result);

paimon-core/src/main/java/org/apache/paimon/mergetree/compact/LookupMergeFunction.java

@@ -25,7 +25,7 @@
 
 import javax.annotation.Nullable;
 
-import java.util.LinkedList;
+import java.util.List;
 
 /**
  * A {@link MergeFunction} for lookup, this wrapper only considers the latest high level record,
@@ -35,36 +35,41 @@
 public class LookupMergeFunction implements MergeFunction<KeyValue> {
 
     private final MergeFunction<KeyValue> mergeFunction;
-    private final LinkedList<KeyValue> candidates = new LinkedList<>();
     private final InternalRowSerializer keySerializer;
     private final InternalRowSerializer valueSerializer;
+    private final LookupMergeRecordManager recordManager;
 
     public LookupMergeFunction(
             MergeFunction<KeyValue> mergeFunction, RowType keyType, RowType valueType) {
         this.mergeFunction = mergeFunction;
         this.keySerializer = new InternalRowSerializer(keyType);
         this.valueSerializer = new InternalRowSerializer(valueType);
+        this.recordManager = new LookupMergeRecordManager();
     }
 
     @Override
     public void reset() {
-        candidates.clear();
+        recordManager.reset();
     }
 
     @Override
     public void add(KeyValue kv) {
-        candidates.add(kv.copy(keySerializer, valueSerializer));
+        recordManager.add(kv.copy(keySerializer, valueSerializer));
     }
 
     @Override
     public KeyValue getResult() {
+        return getResult(recordManager.getCandidates());
+    }
+
+    KeyValue getResult(List<KeyValue> candidates) {
         mergeFunction.reset();
         candidates.forEach(mergeFunction::add);
         return mergeFunction.getResult();
     }
 
-    LinkedList<KeyValue> candidates() {
-        return candidates;
+    LookupMergeRecordManager recordManager() {
+        return recordManager.copy();
     }
 
     public static MergeFunctionFactory<KeyValue> wrap(

paimon-core/src/main/java/org/apache/paimon/mergetree/compact/LookupMergeRecordManager.java

@@ -0,0 +1,102 @@
+/*
+ * 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.mergetree.compact;
+
+import org.apache.paimon.KeyValue;
+import org.apache.paimon.data.InternalRow;
+
+import javax.annotation.Nullable;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Objects;
+import java.util.function.Function;
+import java.util.stream.Collectors;
+
+/** A maintainer of records added to {@link LookupMergeFunction}. */
+class LookupMergeRecordManager {
+
+    private final List<KeyValue> candidates;
+    private final List<Integer> highLevelIndex;
+    private KeyValue highLevel = null;
+
+    LookupMergeRecordManager() {
+        this.candidates = new ArrayList<>();
+        this.highLevelIndex = new ArrayList<>();
+    }
+
+    private LookupMergeRecordManager(List<KeyValue> candidates, List<Integer> highLevelIndex) {
+        this.candidates = candidates;
+        this.highLevelIndex = highLevelIndex;
+    }
+
+    void add(KeyValue kv) {
+        candidates.add(kv);
+        if (kv.level() != 0) {
+            highLevelIndex.add(candidates.size() - 1);
+            highLevel = kv;
+        }
+    }
+
+    void reset() {
+        candidates.clear();
+        highLevelIndex.clear();
+        highLevel = null;
+    }
+
+    List<KeyValue> getCandidates() {
+        return getCandidates(null);
+    }
+
+    List<KeyValue> getCandidates(@Nullable Function<InternalRow, KeyValue> lookup) {
+        setHighLevel();
+
+        if (lookup != null && highLevel == null) {
+            InternalRow lookupKey = candidates.get(0).key();
+            highLevel = lookup.apply(lookupKey);
+        }
+
+        List<KeyValue> copy = new ArrayList<>(candidates);
+        for (int i = 0; i < highLevelIndex.size() - 1; i++) {
+            copy.set(i, null);
+        }
+
+        return copy.stream().filter(Objects::nonNull).collect(Collectors.toList());
+    }
+
+    private void setHighLevel() {
+        if (!highLevelIndex.isEmpty()) {
+            this.highLevel = candidates.get(highLevelIndex.get(highLevelIndex.size() - 1));
+        }
+    }
+
+    boolean containsLevel0() {
+        return candidates.size() > highLevelIndex.size();
+    }
+
+    @Nullable
+    KeyValue highLevel() {
+        return highLevel;
+    }
+
+    LookupMergeRecordManager copy() {
+        return new LookupMergeRecordManager(
+                new ArrayList<>(this.candidates), new ArrayList<>(this.highLevelIndex));
+    }
+}