Memory Management of SAP HANA

Question

Hi All,
I went through one of the documentation in SAP HANA Memory management .
http://www.saphana.com/servlet/JiveServlet/download/2299-2-12806/HANA_Memory_Usage_v2.pdf
This gave me a really good understanding about the Memory management of HANA . Queries for Used and Resident memory and comparison with Overview tab numbers
I had few questions , Which was almost answered in other discussed in one :
But i still have few questions about  Resident and  used memory
Used Memory : Code + Tables + DB Managment
Resident :  what is the formula or content ?
What does this picture refers to ?
Infact the below statements are bit confusing
When memory is required for table growth or for temporary computations, the SAP HANA code obtains it from the existing memory pool. When the pool cannot satisfy the request, the HANA memory manager will request and reserve more memory from the operating system. At this point, the virtual memory size of the HANA processes grows.
Once a temporary computation completes or a table is dropped, the freed memory is returned to the memory manager, who recycles it to its pool, usually without informing Linux6. Thus, from SAP HANA’s perspective, the amount of Used Memory shrinks, but the process’ virtual and resident sizes are not affected. This creates a situation where the Used Memory may even shrink to below the size of SAP HANA’s resident memory, which is perfectly normal.
My doubt here is how  in any given point of time used memory can go below the used memory , because resident memory is always loaded with what is there in used memory , When used memory itslef is less , what does resident contains extra .
Also how to make a relation with HANA used memory , Database Resident memory , Virtual memory .
In case of  a memory issue , what should we check , Used memory of HANA   OR resident memory of HANA  ?
Thanks,
Razal

Answer 1

Hi  all,
I am trying understand memory part bit in details ,  as i am building a complete monitoring infrastructure for HANA , and memory is core of HANA  all part of HANA
Can you also help me to understand how to make some difference  for used memory in HANA and Resident memory
When we say that the Resident memory is something from OS point of view  , this is the memory of the OS which is really being used .
So if the  used memory from HANA Perspective is full , OS still have some free memory  which can be used , How that part is managed .
When i say we are out of memory ,  Both used memory from HANA
Resident memory from OS is full ?
OR does the used memory is simply a calculation of Code + table + etc from HANA point of view .
When execute query :
SELECT SERVICE_NAME,ROUND(SUM(TOTAL_MEMORY_USED_SIZE/1024/1024/1024), 2) AS
"Used Memory GB", ROUND(SUM(PHYSICAL_MEMORY_SIZE/1024/1024/1024), 2) AS
"DB RESIDENT Memory GB" FROM SYS.M_SERVICE_MEMORY GROUP BY SERVICE_NAME
  SERVICE_NAME     Used Memory GB DB RESIDENT Memory GB
1 nameserver         6.73           1.7                 
2 preprocessor       5.38           0.24                
3 indexserver        9.19           4.35                
4 scriptserver       7.52           1.83                
5 statisticsserver  8.52           3.87                
6 xsengine          7.92           1.82                
7 compileserver    5.31           0.23                
On top of all this , In admin view  i get used memory as 17.87 as used memory and 18.89 as peak  .
How this used memory is summed up in admin view .
I am using version 70 .
Thanks,
Razal