2.2.7 Change Propagation

After tables are loaded into HeatWave, data changes are automatically propagated from InnoDB tables on the MySQL DB System to their counterpart tables in the HeatWave Cluster.

DML operations, INSERT, UPDATE, and DELETE, on the MySQL DB System do not wait for changes to be propagated to the HeatWave Cluster; that is, DML operations on the MySQL DB System are not delayed by HeatWave change propagation.

Data changes on the MySQL DB System node are propagated to HeatWave in batch transactions. Change propagation is initiated as follows:

• Every 200ms.

• When the change propagation buffer reaches its 64MB capacity.

• When data updated by DML operations on the MySQL DB System are read by a subsequent HeatWave query.

A change propagation failure can cause tables in HeatWave to become stale, and queries that access stale tables are not offloaded to HeatWave for processing.

Tables that have become stale due to change propagation failures resulting from out-of-code errors are automatically reloaded. A check for stale tables is performed periodically when the HeatWave Cluster is idle.

If change propagation failure has occurred for some other reason causing a table to become stale, you must unload and reload the table manually to restart change propagation for the table. See Section 2.5.1, “Unloading Tables”, and Section 2.2, “Loading Data to HeatWave MySQL”.

To check if change propagation is enabled globally, query the rapid_change_propagation_status variable:

mysql> SELECT VARIABLE_VALUE
          FROM performance_schema.global_status
          WHERE VARIABLE_NAME = 'rapid_change_propagation_status';
+----------------+
| VARIABLE_VALUE |
+----------------+
| ON             |
+----------------+

To check if change propagation is enabled for individual tables, query the POOL_TYPE data in HeatWave Performance Schema tables. RAPID_LOAD_POOL_TRANSACTIONAL indicates that change propagation is enabled for the table. RAPID_LOAD_POOL_SNAPSHOT indicates that change propagation is disabled.

mysql> SELECT NAME, POOL_TYPE
          FROM rpd_tables,rpd_table_id 
          WHERE rpd_tables.ID = rpd_table_id.ID AND SCHEMA_NAME LIKE 'tpch';
+---------------+-------------------------------+
| NAME          | POOL_TYPE                     |
+---------------+-------------------------------+
| tpch.orders   | RAPID_LOAD_POOL_TRANSACTIONAL |
| tpch.region   | RAPID_LOAD_POOL_TRANSACTIONAL |
| tpch.lineitem | RAPID_LOAD_POOL_TRANSACTIONAL |
| tpch.supplier | RAPID_LOAD_POOL_TRANSACTIONAL |
| tpch.partsupp | RAPID_LOAD_POOL_TRANSACTIONAL |
| tpch.part     | RAPID_LOAD_POOL_TRANSACTIONAL |
| tpch.customer | RAPID_LOAD_POOL_TRANSACTIONAL |
+---------------+-------------------------------+

See Section 2.18.1, “Change Propagation Limitations”.