HIVE-28622: Duplicate Entries in TXN_WRITE_NOTIFICATION_LOG Due to Or…

…acle's Handling of Empty Strings

In Oracle, empty strings ('') are treated as NULL values for VARCHAR2 and CHAR data types. This behavior is unique to Oracle and can be confusing, as an empty string is typically considered distinct from NULL in other databases.

As a result, the TXN_WRITE_NOTIFICATION_LOG table receives duplicate entries for a single Hive ACID transaction involving MERGE statements.

This discrepancy leads to issues: the _files and _dumpmetadata files in a Hive ACID incremental dump will not align if the dump scope includes one or more MERGE statements. Consequently, the Hive ACID incremental LOAD fails at the target (DR), blocking subsequent replication executions.

Solution
* Add additional check for partition being null

Testing:
* Tested on cluster with oracle and mysql as backend database

hcatalog/server-extensions/src/main/java/org/apache/hive/hcatalog/listener/DbNotificationListener.java

@@ -1205,7 +1205,7 @@ private void addWriteNotificationLog(List<NotificationEvent> eventBatch, List<Ac
     String select = sqlGenerator.addForUpdateClause("select \"WNL_ID\", \"WNL_FILES\" from" +
             " \"TXN_WRITE_NOTIFICATION_LOG\" " +
             "where \"WNL_DATABASE\" = ? " +
-            "and \"WNL_TABLE\" = ? " + " and \"WNL_PARTITION\" = ? " +
+            "and \"WNL_TABLE\" = ? " + " and (\"WNL_PARTITION\" = ? OR \"WNL_PARTITION\" IS NULL) " +
             "and \"WNL_TXNID\" = ? ");
     List<Integer> insertList = new ArrayList<>();
     Map<Integer, Pair<Long, String>> updateMap = new HashMap<>();