High DB Resident consumption + Unload table process from memory

[Former Member]

Hi SAP experts,

I need your great help!

We have implemented the HANA accelerators for all standard scenarios available and some custom programs, as well as the HANA Live package for critical areas (almost 200 tables replicated in real time). Now we are facing issues in HANA productive related to DB Resident consumption (see attached) and I have realized that indexserver logs has increased significantly.

My questions are:

1) How can I check which specific process is causing this issue? Reset Memory Statistics would be a good practice to release space?

2) I read that HANA has an automatic process to unload tables and release memory space. Does it work only for virtual memory? Besides this process is it a good practice to do the manual unload?

3) Is it possible find by period how many unloads tables were done automatically? I know the general query select * from "M_CS_UNLOADS" but it is not specified by period.

Sorry for many questions. I really appreciate your comments for these points.

Thanks in advance.

Best Regards,

Amanda

[lbreddemann · Accepted solution]

1) Memory shortage is a system wide problem and often not a single process but a whole set of processes lead to the situation. The "one bad process" situation is rather seldom.

2) Not sure what you mean by the "virtual memory" point here. And no, it's not good practice to manually trigger unloads. SAP HANA keeps track on which memory structures can go and will unload them if needed (and only then).

As a rule of thumb: more often than not OOM problems are due to undersized systems.

3) M_CS_UNLOADS contains a timestamp that can be used for splitting into periods.

You may use Solution Manager for a more user appealing experience or the monitoring scripts of SAP note 1969700.

Also, make sure to read SAP note

1999997 - FAQ: SAP HANA Memory

and the referenced material.

- Lars

[Former Member · Accepted solution]

Hi Lars,

Thanks a lot for your support!

Do you think a could do anything to reduce the DB Resident Memory consumption?

We execute a PS transaction to read data from HANA and now we get yellow alert, almost 96% of the total memory used.

Best Regards,

Amanda

[lbreddemann · Accepted solution]

Based on the screenshots you attached I don't see a problem at all.

SAP HANA will typically grab around 90+% of the available memory in the machine at startup time.

Even if the memory later on won't be used, SAP HANA allocates the memory from the OS and keeps it to itself. That's fine, as SAP HANA can assume that, if no limit is provided, it is the only relevant memory user on the machine.

The advantage of this is: we get large contagious mem areas allocated AND we don't have to go back to the OS every other second and ask for more memory.

- Lars