Is the in-memory Hana system a permanent or temporary storage area ?

[Former Member]

More explicitly my question would be ... does the in-memory Hana system keep the database tables permanently in memory or does it keep them temporarily ?

[Former Member · Accepted solution]

HDB is stores in Memory and HDD also, updating data both sides according save point & commit concept like normal RDBMS, but when you read data it takes from memory according table types.

So hope you cleared above answers.

Thanks

Rao

[Former Member · Accepted solution]

Thanks for your reply

[Former Member]

Hello,

IMDB has 2 areas 1) Memory (RAM) and SSD (Super fast Solid State Disks). The moment you check how much space you need for your reporting (e.g. for COPA how much tables you need to access while reporting it) that data will reside on Memory and save points for the same will go to SSDs.

As one of the contributor has written about write-ahead-logging implemented, so before a COMMIT is returned all changes have been written to the database redologs (savepoints).

Hopefully it will answer your questions..

PY

[WMuellner]

It can be seen as a 'permanent' in-memory concept.

Of course data from memory is 'lost' if you unplug the power but during normal operations data from in-memory tables is continuousely saved to disk storage (fast rotating disks and superfast SSDs, or superfast SSDs only ).

In case of power failure the system can simply be restarted and - if the disks are not damaged - can be brought up to the last 'committed' state before the failure. Then it will re-load data from the disks and continue operating like before with tables 'in-memory'.

hth, Walter

PS: and there is the concept of tables being explicitely un-loaded from/loaded into memory...

[lbreddemann]

It should be pointed out, that the persistence of HANA really is similar to the persistence of any other DBMS.

There's write-ahead-logging implemented, so before a COMMIT is returned all changes have been written to the database redologs.

Maybe it's time to get this point clearer:

ALL databases supported by SAP always work in data that is in-memory.

Seen that way, there is no such thing as a non-in-memory database.

The big difference with HANA is that ALL data is kept in memory most of the time.

The data storage structures are optimized for this situation and not for having most of the data on disk as this is the case with standard DBMS platforms.

Also, the data processing schemes have been optimized to perform better with heavy-parallel data access, that means that there are other algorithms used e.g. for hashing data.

So, storage wise HANA is pretty conservative. And in terms of data security this is probably not a bad thing...

regards,

Lars

[former_member93896]

In general tables are kept in memory permanently. However, it's also possible to create temporary tables.

Regards,

Marc

SAP Customer Solution Adoption (CSA)