In SAP HANA, the Persistence Layer is responsible for managing the storage and retrieval of data from disk. It ensures the durability of data by storing it persistently even when the system is shut down. The persistence layer in SAP HANA consists of the following components:
Disk-based Persistence:
SAP HANA retains data on disk to ensure durability. While the main focus is on in-memory processing for speed, data is periodically saved to disk to prevent data loss in case of system failure.
Persistence Layer Services:
The Persistence Layer Services handle tasks related to data persistence, such as logging and saving data to disk. It includes components like the Log Area and Data Area.
Log Area:
The Log Area is a critical part of the persistence layer. It stores transaction logs, which record changes to data before they are applied to the actual data in memory. This allows for the recovery of transactions in the event of a system failure.
Data Area:
The Data Area stores the actual data persistently on disk. It includes the columnar storage of tables and other data structures. The data in the Data Area is loaded into memory when the system starts.
Savepoints:
Savepoints are specific points in time when the entire data in memory is saved to disk. This process ensures that even if the system goes down, the data can be restored to a consistent state using the saved information on disk.
Recovery Mechanisms:
The persistence layer provides recovery mechanisms to ensure data consistency after a system failure. It uses transaction logs and savepoints to recover the database to a consistent state during system restart.
Redundancy and Fault Tolerance:
The persistence layer incorporates mechanisms for data redundancy and fault tolerance. This includes data replication and backup strategies to protect against hardware failures.
Data Lifecycle Management:
Data Lifecycle Management (DLM) is a part of the persistence layer that manages the lifecycle of data, including archiving and data aging. It ensures that data is efficiently managed over time, considering factors such as access frequency and retention policies.
Backup and Restore:
The persistence layer provides tools and services for creating backups of the database. This is crucial for disaster recovery and for ensuring that data can be restored in case of data corruption or loss.
Asynchronous Persistence:
The persistence layer in SAP HANA operates asynchronously, allowing the in-memory processing to continue independently of disk-based persistence activities. This asynchronous nature helps maintain high performance for real-time analytics.
By incorporating these components and features, the persistence layer in SAP HANA ensures the durability, consistency, and recoverability of data, contributing to the overall reliability of the system.
