Propagating In-memory Updates to Disk

As mentioned, during batch operations Vector automatically propagates the changes buffered in memory to disk-resident tables (Update Propagation).

As well, the COMBINE command can be used manually to write the data from all completed, cached, INSERT/UPDATE/DELETE statements that reside in memory to disk files and to optimize the table layout.

To propagate ALL in-memory updates to disk files for all tables, use the following SQL statement:

CALL VECTORWISE(COMBINE);

To propagate in-memory updates to a specific table to disk:

CALL VECTORWISE(COMBINE 'table_name'); or

MODIFY … TO COMBINE;

Note: The performance cost of the COMBINE method can be significant because it is roughly proportional to the total volume of data in the table. As such, it should be used only when modifying a significant percentage of a table. The benefit of this approach is that it allows large modifications, results in lower memory consumption, mand provides higher processing performance after the update.