Delta merges in SAP HANA

 

Delta merges in SAP HANA:

The 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 storage's exist

The delta merges, but in some parts the focus is extended to other functionalities that are also found in the monitoring view M_DELTA_MERGE_STATISTICS.

Delta merges and optimize compression runs are sometimes (e.g. in error messages) referred to as "table optimizations".