[GitHub] [flink-table-store] JingsongLi commented on a diff in pull request #104: [FLINK-27336] Avoid merging when there is only one record

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

JingsongLi commented on code in PR #104:
URL: https://github.com/apache/flink-table-store/pull/104#discussion_r912611645


##########
flink-table-store-core/src/main/java/org/apache/flink/table/store/file/mergetree/compact/MergeFunctionHelper.java:
##########
@@ -0,0 +1,73 @@
+/*
+ * 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.table.store.file.mergetree.compact;
+
+import org.apache.flink.table.data.GenericRowData;
+import org.apache.flink.table.data.RowData;
+
+import static org.apache.flink.table.store.file.mergetree.compact.ValueCountMergeFunction.count;
+
+/** Helper functions for the interaction with {@link MergeFunction}. */
+public class MergeFunctionHelper {
+
+    private final MergeFunction mergeFunction;
+
+    private RowData rowData;
+    private boolean isInitialized;
+
+    public MergeFunctionHelper(MergeFunction mergeFunction) {
+        this.mergeFunction = mergeFunction;
+    }
+
+    /**
+     * Resets the {@link MergeFunction} helper to its default state: 1. Clears the one record which
+     * the helper maintains. 2. Resets the {@link MergeFunction} to its default state. 3. Clears the
+     * initialized state of the {@link MergeFunction}.
+     */
+    public void reset() {
+        rowData = null;
+        mergeFunction.reset();
+        isInitialized = false;
+    }
+
+    /** Adds the given {@link RowData} to the {@link MergeFunction} helper. */
+    public void add(RowData value) {
+        if (rowData == null) {
+            rowData = value;
+        } else {
+            if (!isInitialized) {
+                mergeFunction.add(rowData);
+                isInitialized = true;
+            }
+            mergeFunction.add(value);
+        }
+    }
+
+    /**
+     * Get current value of the {@link MergeFunction} helper. Return null if the value should be
+     * skipped.
+     */
+    public RowData getValue() {
+        return isInitialized
+                ? mergeFunction.getValue()
+                : mergeFunction instanceof ValueCountMergeFunction

Review Comment:
   Just `rowData`?
   The input of `ValueCountMergeFunction` should not be count zero.



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