System Architecture

Shared-Nothing

For scalability support, SAP HANA uses multiple servers in one cluster and partitions the data to distribute across the servers with a shared-nothing architecture. The system has three components. The Name servers keep track of the location of data and store information on the topology of the entire system. The Index servers contain the actual data partitions and process the data as required. The last component is Statistics servers which collect information about status, performance and resource consumption from the system.

Concurrency Control

Multi-version Concurrency Control (MVCC)

SAP HANA supports Multi-version Concurrency Control as the default mechanism to ensure data consistency. When one user connects to the database, a snapshot is provided for each user. The changes from one writer can only be seen by others after transactions are committed. No rollback segment is supported for the insert method. Both distributed locking with a global deadlock detection mechanism and distributed snapshot isolation are supported in SAP HANA to achieve synchronization. Moreover, one optional background garbage collection thread is also supported.

Indexes

B+Tree Hash Table

SAP HANA supports various indexes, which contain B+ tree, Compressed Prefix-B+ Tree, and Inverted index.

Storage Architecture

In-Memory

SAP HANA is an in-memory database. It uses In-Memory Computing technologies to store data in memory with a complicated data compression, which will improve the performance by avoiding disk I/O. Permanent storage of the data on disk is still required to achieve fault tolerance and the back-up operations will be executed asynchronously as a background task which will not influence the performance.

Stored Procedures

Supported

SAP HANA supports stored procedure features by allowing clients to describe a sequence of data transformations and define as a reusable processing block. A Procedure can be created with SQP HANA SQL queries or Using the Modeler wizard (Modeler and Development perspectives). The stored procedures can be parameterized and reused in another procedure.

Views

Virtual Views Materialized Views

SAP HANA supports both materialized and virtual views. When a materialized view is created, the system validates the definition and precomputes the result set from the database, which is stored on disk to improve the performance. SAP HANA also allows virtual views which replace the stored result set by on-the-fly calculation and are derived each time when they are used.

Storage Model

Decomposition Storage Model (Columnar) N-ary Storage Model (Row/Record)

SAP HANA supports both N-ary Storage Model and Decomposition Storage Model. However, it is optimized for DSM as a default storage model in order to provide high performance on a hybrid workloads of analysis and transaction. SAP HANA allows joining row-oriented tables with column-oriented tables and also supports altering the storage model of an existing table.

Query Execution

Vectorized Model

Isolation Levels

Read Committed

In SAP HANA, the default isolation level is ReadCommited, and the maximum one is Serialization. Snapshot Isolation is not supported by default.

Query Compilation

JIT Compilation

Joins

Nested Loop Join Hash Join

Hash Join and Nested Loop Join are supported by SAP HANA. Different variants of Hash Join are mainly used in SAP HANA.

Foreign Keys

Supported

SAP HANA supports foreign key constraints to enforce integrity.

Checkpoints

Fuzzy

SAP HANA supports fuzzy checkpoints, where any updates are still stored in storage snapshots even if transactions are not committed. Extra work are needed to remove those updates. Moreover, SAP HANA also supports encrypted snapshots when database is encrypted first.

Data Model

Column Family / Wide-Column

SAP HANA is based on the columnar structure, where data are stored in columns to minimize the storage footprint, since repeating values are only stored once. It is easier to change other structures to columnar structure in SAP HANA, because memory is much faster.