BW on HANA: Can a HANA DB system 'overcommit' its memory - only part of DB in memory?

[tombo_larsen]

Hi Guys

Lets say that we buy a single-node HANA hardware appliance with 512 GB memory and a HANA DB for SAP BW - after performing a sizing with this result.

After one year the BW database has grown unexpected and don't fit into this memory (512 GB) anymore.

Will HANA DB be able to run this larger database (with decreased performance) - 'overcommting' its memory, having some data in memory and other only on persistence storage?

...or will HANA DB simply crash - as if *ALL* data/database always must be able to fit into physical memory?

Br

Tom Bo

[former_member184768 · Accepted solution]

Hi Tom Bo,

In my point of view,

• When you mention DB has grown, it means the physical table size has grown beyond allocation limit. This is possible PROVIDED not all the data is loaded to the memory. It can be on the disk, but not in memory.
• If you wish to load ALL the data to memory, I don't think HANA will allow you to do so, that is, load data in the memory beyond allocated limit (actually maximum of about 20 - 30 % less than allocation limit).
• You might get early indications as your data loads will start failing, if there is no sufficient memory available for data load operations.
• You may have to unload objects from memory, but may not be able to load them back to the memory if it is already occupied.

• Now if you wish to keep the data to disk and load only selective data to memory within the permissible limit, then it would work, provided you have sufficient memory available for run time operations (query execution, sorts / merges etc).
• It is not mandatory to have ALL the data in memory if you don't wish to use it.
• With SPS 5 and BW SP08, SAP is coming with HOT / WARM / COLD concept which can help you manage the data in memory.

Regards,

Ravi

[former_member184768 · Accepted solution]

Please refer to the following PDF (thanks to Anooj for posting it today), which will help you understand the concept of HOT / WARM / COLD data in BW on HANA.

http://www.experiencesaphana.com/servlet/JiveServlet/download/38-7925/SAP%20NetWeaver%20BW%207%203on...

Regards,

Ravi

[Former Member · Accepted solution]

Hi Ravi,

how do You set the Allocation limit ?

Can this be done online ?

ThanXs

Martin