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This blog provides additional details about the new concept in HANA to manage “warm“ data in BW. It is follows up on my blog where I initially introduced this idea: Update – Data LifeCycle Management for BW-on-HANA
What are deployment options for HANA Extension Nodes?
There are basically three different deployment options for extension nodes in HANA system for BW. Which option you choose depends on your landscape, the sizing for the amount of “warm” data in your system, BW release, HW partner, … and, of course, the timeline.
Why does it work for BW?
The standard HANA sizing guidelines allow for a data footprint of 50% of the available RAM. This ensures that all data can be kept in RAM at all times and there is sufficient space for intermediate result sets. These sizing guidelines can be significantly relaxed on the Extension Group, since “warm” data is accessed
- less frequently,
- with reduced performance SLAs,
- with less CPU-intensive processes,
- only partially at the same time.
The BW application controls and understands the access patterns to BW tables and derives appropriate partitioning and table distribution for “warm” tables. This way BW ensures that a “warm data” table is not loaded completely to memory, but only partially due to efficient partition pruning. The load to memory of the much smaller table partitions is not critical in the usual BW operations (batch load processes).
Based on the modelling object type BW can automatically provide a very good default for the “warm” setting.
- Up to 50% of BWs data can be classified as “warm” (experience with “non-active” data concept)
- access to “warm” tables is partition-based in >95% of all cases (write(=merge)&read)
- data in “warm” tables is part of batch processes in most cases (load-to-memory not critical)
- query access to “warm” data will be significantly slower – must be accepted/part of the deal
How to classify BW objects as “warm”?
The classification of a BW object as “warm” is part of the modeling task in the corresponding modeling UI. The default for all objects is “hot”.
- A newly created object classified as “warm” has all its database tables created on the “extension” node(s)
- An object containing data does not change the location of its tables immediately during object activation, but only changes the metadata of the object. To move the tables there are two alternatives:
- Execute a table redistribution using the SAP DWF DataDistributionOptimizer (DDO) – this can be seen like a regular house-keeping action,
- Use transaction RSHDBMON to move single tables/partitions manually.
What type of objects can be classified as “warm” in BW?
This paragraph describes which BW objects can be classified as “warm” and in which BW release the option is available. It does not mean that all these objects necessarily should be classified as “warm” – it depends on the individual use case.
BW Object | Available release | Comment | Caution |
InfoCubes | not available | Please look at the options for advanced DSOs | |
Classic DSOs (exception see below) | not available | Please look at the options for advanced DSOs | |
DataSources/PSA tables | BW7.4 SP10 | A PSA table can be classified as “warm”. PSA tables are partitioned grouping together one or more load requests. Load operations only change the latest partition --> small amount of data for the MERGE process. Extract operations only use the latest partition in most cases (delta loads). | |
Write-optimized DSOs | BW7.4 SP10 | See PSA comment | Only write-optimized DSOs with usage type Corporate Memory should be classified as “warm”. I.e. no reporting access, no heavy look-up usage |
Advanced DSOs w/o Activation | BW7.4 SP10 & BW/4HANA | Partitioning and access similar to PSA | See w-o DSO |
Advanced DSOs w/ Activation | BW7.5 SP01 & BW/4HANA | Load and Extract patterns are request/partition-based – similar to PSA tables | DSO-activation needs to load and process the complete table in memory è only aDSOs should be classified as “warm” with very infrequent load activity; use RANGE partitioning of the aDSO where possible to allow pruning |
Advanced DSOs with reporting access | BW7.5 SP01 & BW/4HANA | Load patterns are request/partition-based – similar to PSA tables | Query read access may load the complete table (all requested attributes/fields) to memory and query processing may be very CPU-intensive. Only classify objects with
|
RANGE- Partitions of Advanced DSOs | BW/4HANA | Selected RANGE partitions of aDSOs can be classified as “warm”. Load and Read patterns are request/partition-based – similar to PSA tables. | DSO-activation does partitioning pruning and loads and processes the complete partitions to memory --> only aDSOs partitions should be classified as “warm” with very infrequent load activity |
What is the impact for the HANA system?
A HANA system with extension node(s) first of all looks and behaves like a standard HANA scale-out system. All operations and features&functions work as before (like system replication, …).
However there are a few things that should be considered:
- The HANA system can now store more data, which has an impact on backup and recovery times. Especially the higher data volumes on the extension node(s) may now dominate the backup and recovery times – these depends on the hardware for the HANA system.
- Forced unloads are now very common on the extension node(s). On the “hot” nodes many unloads are a sign of insufficient sizing.
- In option 3 and – possibly depending on the choice of hardware – also in option 2, the setup of High Availability using host-auto-failover may need to be adjusted. If no dedicated standby for the extension node exists, it may be necessary to explicitly fall back to the original configuration as soon as a failing node is brought online again.
- For non-BW data the classification “warm” with the re-location to the Extension Node(s) is not supported. If non-BW data is stored in the same HANA DB this data has to be located on the classic nodes.
When will the new concept be available?
Options 1 and 2 are generally released since the Datacenter Service Point (DSP) of HANA SP12.
Offerings for option 3 are still under discussions.
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