[dropcap]H[/dropcap]ana Data Structure has two components namely Main Storage & Delta Storage.
|Data Structure||Access Pattern||Compression|
|Main Storage||Optimized for read access||Advanced|
|Delta Storage||Optimized for write access||Basic|
- Read operations are performed on both structures, while write operations only affect the delta.
Main Storage in HANA
The main storage contains the main part of the data (data compression).
Delta storage in HANA
Write operations on the finely compressed data in main storage would be costly. Hence, write operations don’t modify compressed data in the main storage. Instead, all the relevant changes are written to a separate data structure known as the delta storage.
The delta storage itself exists only in the memory part & is not persisted to disk.
Delta merge Operation in HANA
The main purpose of the delta merge operation is generally to move the changes collected in the delta storage to read-optimized main storage section.