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

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

SteNicholas commented on code in PR #104:
URL: https://github.com/apache/flink-table-store/pull/104#discussion_r860401394


##########
flink-table-store-core/src/main/java/org/apache/flink/table/store/file/mergetree/SortBufferMemTable.java:
##########
@@ -166,19 +169,31 @@ private void advanceIfNeeded() {
                 if (previousRow == null) {
                     return;
                 }
-                mergeFunction.reset();
-                mergeFunction.add(previous.getReusedKv().value());
 
+                boolean hasOne = true;
                 while (readOnce()) {
                     if (keyComparator.compare(
                                     previous.getReusedKv().key(), current.getReusedKv().key())
                             != 0) {
                         break;
                     }
+                    // avoid merging when there is only one record
+                    if (hasOne) {
+                        mergeFunction.reset();
+                        mergeFunction.add(previous.getReusedKv().value());
+                        hasOne = false;
+                    }
                     mergeFunction.add(current.getReusedKv().value());
                     swapSerializers();
                 }
-                result = mergeFunction.getValue();
+                RowData previousValue = previous.getReusedKv().value();
+                result =
+                        hasOne
+                                ? mergeFunction instanceof ValueCountMergeFunction

Review Comment:
   @JingsongLi, in theory the count should never be zero, but in current tests there is 0 test case. Hence I add this logic to avoid the zero situation.



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