What delta merge process in SAP HANA database?
The delta merge process in SAP HANA is a key feature for optimizing the performance and efficiency of the database. HANA stores data in columnar tables, and these tables have two main storage components: the main store and the delta store.
Here's an overview of the delta merge process:
Components:
A: Main Store:
- This is the read-optimized part of the table.
- It contains a large, compressed, and read-optimized set of data.
- Data in the main store is immutable.
- This is the write-optimized part of the table.
- It handles new inserts, updates, and deletes.
- It is not as compressed or read-optimized as the main store.
The Need for Delta Merge
The delta merge process is necessary because while the delta store is efficient for write operations, it becomes inefficient for read operations as it grows. Frequent writes lead to an accumulation of data in the delta store, which can degrade read performance over time.
Benefits
- Improved Read Performance: By consolidating data into the main store, read operations become more efficient.
- Optimized Storage: The main store's data compression techniques are applied, reducing the storage footprint.
- Data Consistency: Ensures that the data is consistent and up-to-date between the main and delta stores.
Considerations
- Resource Intensive: The merge process can be resource-intensive, potentially affecting system performance. Hence, it's often scheduled during off-peak hours.
- Frequency of Merges: The frequency of merges can be configured based on the specific requirements and workload of the HANA system.
Conclusion
The delta merge process is essential for maintaining the performance and efficiency of SAP HANA databases. By balancing the needs for write optimization (handled by the delta store) and read optimization (handled by the main store), HANA ensures that it can handle both high transaction rates and complex queries effectively.