Balancing cost and performance with SAP HANA Data Tiering

 

SAP HANA is an in-memory database and is only supported on certified hardware. By requiring certified hardware, SAP is making sure that core-to-memory ratio is respected. The core-to-memory ratio is the key to guaranteeing optimal performance. Certified hardware unfortunately doesn’t come cheap. The in-memory and column store capabilities of SAP HANA enable access to data at an incredible speed. The question is, do you need fast access to all data, all the time? The cost of keeping all the data in memory may not be justifiable. Most users find that slower access to old or rarely used data is acceptable.

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Data aging

Aging is the process of becoming older—something all of us have to undergo, like it or not. Data is also subject to aging. As time goes by, data will be less and less accessed or even updated. Data aging is a data management concept to reduce the SAP HANA memory footprint based on the data aging framework. Data aging is available in SAP ERP on SAP HANA and in SAP S/4HANA and can move large amounts of data from hot to warm storage to free working memory for younger data. Data ages from operationally relevant or hot data to data no longer accessed during normal operation or cold data. The data temperature can be used to partition tables to optimize resource consumption and performance and to move data between hot, warm, and cold partitions. Hot data is stored in memory, warm data is stored primarily on disk, and cold data is stored outside of the SAP HANA system. Data can be divided according to age and the number of times it is accessed.

SAP has different data tiering options for hot, warm, and cold data, which can be used in combination with SAP HANA:

Hot data

Hot data is stored in memory. For performance reasons, SAP HANA loads the column tables into memory. Standard DRAM is still volatile, meaning if the SAP HANA instance is restarted, whether for maintenance or after a failure, all data needs to be reloaded into memory. This can take up to several hours on large systems. This is where persistent memory comes into play. It has a lower TCO and larger configurations are possible then with DRAM. Data in persistent memory maintains its state after a system shutdown. This reduces database startup time enormously as data no longer needs to be loaded from disk into memory.

Warm data

Warm data is data that is still accessed, although infrequently. It’s between hot and cold data: not accessed enough to load it in main memory but accessed too much to be moved outside of the SAP HANA system to alternative storage locations. Warm data is handled differently according to the applications in use:

  • SAP HANA native storage extension is a warm data store in SAP HANA. It allows the applications to load less-frequently accessed data without fully loading it into memory. It combines in-memory storage with solid state or flash drives to improve the cost-to-performance ratio. With SAP HANA native storage extension, pages can be loaded instead of columns, reducing the memory footprint. Page attributes allows table columns to be loaded by page from the persistency layer into memory without requiring the entire table to be loaded into memory. SAP HANA native storage extension is used by SAP S/4HANA and the SAP Business Suite powered by SAP HANA.
  • An extension node is a dedicated SAP HANA in-memory node for warm data processing. It can be added to an existing SAP HANA database to scale out at a lower cost. It can be used in combination with SAP HANA native applications and SAP BW. An extension node is basically an SAP HANA node with the same functionalities as any other SAP node. Memory and CPU requirements are more relaxed, meaning that they have an extended core-to-memory ratio. An extension node keeps the data on disk only loading it when needed. If memory is scare, the extension node will unload data from memory to disk based on a least recently used algorithm. As the extension node only contains warm data, which is modified less frequently, more data can be loaded into memory as the SAP HANA instance needs less memory for the workspace. Extension nodes need to be deployed on certified SAP HANA hardware. Commodity hardware cannot be used.
  • Another option is SAP HANA dynamic tiering, an add-on to the SAP HANA database. SAP HANA dynamic tiering can be added to an existing SAP HANA database as an extension to create queries and load data into disk-based, column-based database tables called extended tables and multistore tables. SAP HANA dynamic tiering is only supported with SAP HANA native applications. It can be deployed on commodity hardware, making the storing of warm data less expensive.

Cold data

Cold data may be stored on the lowest-cost storage solution as long as it remains accessible to SAP HANA. The SAP HANA spark controller can be used to manage the cold data tier for native SAP HANA applications. The SAP BW near-line storage option can be used with SAP BW and SAP IQ.

Data tiering Picture 2

This post has been adapted from a section of the book SAP HANA 2.0 Administration by Mark Mergaerts and Bert Vanstechelman.

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About the author

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Bert Vanstechelman

Bert Vanstechelman is Managing Partner and Principal Technical SAP Consultant at Expertum. He has more than 25 years of experience in SAP technical consulting, covering countless SAP versions in combination with all kinds of databases and operating systems supported by SAP. Bert specializes in platform migrations, SAP release upgrades, and SAP HANA conversions.

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