Fix TRUNCATE operation not replicated to ClickHouse (issue #155)

- Add TRUNCATE TABLE handling in DbReplicatorRealtime.handle_query_event()
- Implement handle_truncate_query() method to parse and execute TRUNCATE on ClickHouse
- Clear pending insert/delete operations when TRUNCATE is processed
- Add test_truncate_operation_bug_issue_155() to reproduce and verify the fix
- Test confirms TRUNCATE now properly clears data in both MySQL and ClickHouse

Fixes #155

Author: bakwc

mysql_ch_replicator/db_replicator_realtime.py

@@ -191,6 +191,9 @@ def handle_query_event(self, event: LogEvent):
         if query.lower().startswith('rename table'):
             self.upload_records()
             self.handle_rename_table_query(query, event.db_name)
+        if query.lower().startswith('truncate'):
+            self.upload_records()
+            self.handle_truncate_query(query, event.db_name)
 
     def handle_alter_query(self, query, db_name):
         self.replicator.converter.convert_alter_query(query, db_name)
@@ -253,6 +256,35 @@ def handle_rename_table_query(self, query, db_name):
             ch_clauses.append(f"`{src_db_name}`.`{src_table_name}` TO `{dest_db_name}`.`{dest_table_name}`")
         self.replicator.clickhouse_api.execute_command(f'RENAME TABLE {", ".join(ch_clauses)}')
 
+    def handle_truncate_query(self, query, db_name):
+        """Handle TRUNCATE TABLE operations by clearing data in ClickHouse"""
+        tokens = query.strip().split()
+        if len(tokens) < 3 or tokens[0].lower() != 'truncate' or tokens[1].lower() != 'table':
+            raise Exception('Invalid TRUNCATE query format', query)
+
+        # Get table name from the third token (after TRUNCATE TABLE)
+        table_token = tokens[2]
+        
+        # Parse database and table name from the token
+        db_name, table_name, matches_config = self.replicator.converter.get_db_and_table_name(table_token, db_name)
+        if not matches_config:
+            return
+
+        # Check if table exists in our tracking
+        if table_name not in self.replicator.state.tables_structure:
+            logger.warning(f'TRUNCATE: Table {table_name} not found in tracked tables, skipping')
+            return
+
+        # Clear any pending records for this table
+        if table_name in self.records_to_insert:
+            self.records_to_insert[table_name].clear()
+        if table_name in self.records_to_delete:
+            self.records_to_delete[table_name].clear()
+
+        # Execute TRUNCATE on ClickHouse
+        logger.info(f'Executing TRUNCATE on ClickHouse table: {db_name}.{table_name}')
+        self.replicator.clickhouse_api.execute_command(f'TRUNCATE TABLE `{db_name}`.`{table_name}`')
+
     def log_stats_if_required(self):
         curr_time = time.time()
         if curr_time - self.last_dump_stats_time < self.STATS_DUMP_INTERVAL:

test_mysql_ch_replicator.py

@@ -2658,3 +2658,92 @@ def test_issue_160_unknown_mysql_type_bug():
     assert mysql_structure.table_name == 'test_table'
     assert len(mysql_structure.fields) == 17  # All columns should be parsed
     assert mysql_structure.primary_keys == ['id', 'col_e']
+
+def test_truncate_operation_bug_issue_155():
+    """
+    Test to reproduce the bug from issue #155.
+    
+    Bug Description: TRUNCATE operation is not replicated - data is not cleared on ClickHouse side
+    
+    This test should FAIL until the bug is fixed.
+    When the bug is present: TRUNCATE will not clear ClickHouse data and the test will FAIL
+    When the bug is fixed: TRUNCATE will clear ClickHouse data and the test will PASS
+    """
+    cfg = config.Settings()
+    cfg.load(CONFIG_FILE)
+
+    mysql = mysql_api.MySQLApi(
+        database=None,
+        mysql_settings=cfg.mysql,
+    )
+
+    ch = clickhouse_api.ClickhouseApi(
+        database=TEST_DB_NAME,
+        clickhouse_settings=cfg.clickhouse,
+    )
+
+    prepare_env(cfg, mysql, ch)
+
+    # Create a test table
+    mysql.execute(f'''
+CREATE TABLE `{TEST_TABLE_NAME}` (
+    id int NOT NULL AUTO_INCREMENT,
+    name varchar(255),
+    age int,
+    PRIMARY KEY (id)
+); 
+    ''')
+
+    # Insert test data
+    mysql.execute(f"INSERT INTO `{TEST_TABLE_NAME}` (name, age) VALUES ('Alice', 25);", commit=True)
+    mysql.execute(f"INSERT INTO `{TEST_TABLE_NAME}` (name, age) VALUES ('Bob', 30);", commit=True)
+    mysql.execute(f"INSERT INTO `{TEST_TABLE_NAME}` (name, age) VALUES ('Charlie', 35);", commit=True)
+
+    # Start replication
+    binlog_replicator_runner = BinlogReplicatorRunner()
+    binlog_replicator_runner.run()
+    db_replicator_runner = DbReplicatorRunner(TEST_DB_NAME)
+    db_replicator_runner.run()
+
+    # Wait for initial replication
+    assert_wait(lambda: TEST_DB_NAME in ch.get_databases())
+    ch.execute_command(f'USE `{TEST_DB_NAME}`')
+    assert_wait(lambda: TEST_TABLE_NAME in ch.get_tables())
+    assert_wait(lambda: len(ch.select(TEST_TABLE_NAME)) == 3)
+
+    # Verify data is replicated correctly
+    mysql.execute(f"SELECT COUNT(*) FROM `{TEST_TABLE_NAME}`")
+    mysql_count = mysql.cursor.fetchall()[0][0]
+    assert mysql_count == 3
+
+    ch_count = len(ch.select(TEST_TABLE_NAME))
+    assert ch_count == 3
+
+    # Execute TRUNCATE TABLE in MySQL
+    mysql.execute(f"TRUNCATE TABLE `{TEST_TABLE_NAME}`;", commit=True)
+    
+    # Verify MySQL table is now empty
+    mysql.execute(f"SELECT COUNT(*) FROM `{TEST_TABLE_NAME}`")
+    mysql_count_after_truncate = mysql.cursor.fetchall()[0][0]
+    assert mysql_count_after_truncate == 0, "MySQL table should be empty after TRUNCATE"
+
+    # Wait for replication to process the TRUNCATE operation
+    time.sleep(5)  # Give some time for the operation to be processed
+
+    # This is where the bug manifests: ClickHouse table should be empty but it's not
+    # When the bug is present, this assertion will FAIL because data is not cleared in ClickHouse
+    ch_count_after_truncate = len(ch.select(TEST_TABLE_NAME))
+    assert ch_count_after_truncate == 0, f"ClickHouse table should be empty after TRUNCATE, but contains {ch_count_after_truncate} records"
+
+    # Insert new data to verify replication still works after TRUNCATE
+    mysql.execute(f"INSERT INTO `{TEST_TABLE_NAME}` (name, age) VALUES ('Dave', 40);", commit=True)
+    assert_wait(lambda: len(ch.select(TEST_TABLE_NAME)) == 1)
+    
+    # Verify the new record
+    new_record = ch.select(TEST_TABLE_NAME, where="name='Dave'")
+    assert len(new_record) == 1
+    assert new_record[0]['age'] == 40
+
+    # Clean up
+    db_replicator_runner.stop()
+    binlog_replicator_runner.stop()