Professional: HANA Memory Management

Simplified Explanation of SAP HANA Memory Management:

1. Memory in SAP HANA:

• Memory is a key resource for SAP HANA.

• Understanding how it's requested, utilized, and managed is vital for HANA users.

• Memory indicators help monitor, track, and send alerts for usage.

2. Key Memory Indicators:

• Used Memory: Total memory used by SAP HANA. This includes code, data, system tables, and temporary computations.

• Peak Used Memory: Tracks the highest value of used memory over time. This allows for monitoring the maximum memory usage.

3. Memory Allocation:

• SAP HANA operates in the Linux environment.

• Upon startup, the operating system (Linux) reserves memory for SAP HANA for various purposes like code, stack, and static data.

• As SAP HANA operates, it dynamically requests more memory when needed, including heap and shared memory.

• Most of this memory is used for database management, computations, and table storage.

4. Tools for Memory Analysis:

• SAP HANA provides SQL scripts to inspect top peak memory usage and correlate them with specific events or dates. This can be helpful to track and optimize system performance.

5. Resident Memory:

• This is the actual physical memory currently being used.

• Resident memory represents memory used by SAP HANA, the OS, and other programs.

• As processes run, some of the virtual memory gets loaded or mapped to this physical (resident) memory.

• In a well-sized SAP HANA system, swapping is disabled, ensuring consistent performance. Normally, memory used by the OS and other programs won't exceed 2GB, leaving the rest for SAP HANA.

6. Key Points on Resident Memory:

• Memory required by SAP HANA is fetched from an existing memory pool. If this pool can't satisfy the request, HANA asks the OS for more, increasing the virtual memory size.

• Different measurements exist for resident memory:

  • Database Resident: Memory used by SAP HANA processes at the OS level.

  • Total Resident: Overall memory usage in the OS, including other programs.

  • Physical Memory: The total available physical memory on the server.

• High Database Resident memory utilization isn't a concern. But if Total Resident memory is high, it's advised to inspect memory usage in the OS to check for other programs/processes.

• For monitoring, it's recommended to keep an eye on the "Used Memory" metric in SAP HANA Studio or HANA DB Explorer or HANA Cockpit level.

In essence, memory management in SAP HANA is about ensuring that the system has the memory it needs to function efficiently while also providing tools to monitor and analyze usage for optimization.

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