Footprint Reduction and Uniqueness Enforcement with Hash Indices in SAP HANA

Databases commonly use multi-column indices for composite keys that concatenate attribute values for fast entity retrieval. For realworld applications, such concatenated composite keys contribute significantly to the overall space consumption, which is particularly expensive for main memory-resident databases. We present an integer-based hash representation of the actual values for the purpose of reducing the overall memory footprint of a system while maintaining the level of performance. We analyzed the performance impact as well as the memory footprint reduction of hash-based indices in SAP HANA in a real-world enterprise database setting. For a production SAP ERP system, the introduction of hash-based primary key indices alone reduces the entire memory footprint by 10% with comparable performance.