Changes (INSERT, UPDATE, DELETE) to SAP HANA column store tables are not directly updated in the main storage. Instead, the change information is written to a dedicated delta storage:
From time to time the main storage needs to be updated with the content of the delta storage. This operation is called delta merge. The rough execution steps of a delta merge are illustrated in the following picture:
You can see that during a delta merge two separate main and delta storages exist.