Shared Memory Parameter in HANA

Here, I explained about parameter related to shared memory in HANA database and using below parameter we can instruct HANA database whether we need to keep row store data in share memory or not at the time HANA database startup.

1 - keep_shared_memory_over_restart_timeout
2 - reuse_shared_memory_for_restart_timeout
3 - reuse_shared_memory_for_restart
4 - keep_shared_memory_over_restart

1 - keep_shared_memory_over_restart_timeout

Parameter Name      - keep_shared_memory_over_restart_timeout
Default Value           -  3600
About Parameter     - This parameter sets the number of seconds the row store information is stored in shared memory after shutdown.

How to Set Parameter - indexserver.ini -> [row_engine] -> keep_shared_memory_over_restart_timeout

This parameter can be used to define the number of seconds the row store shared memory is kept after a shutdown. The default is 3600 seconds, so a restart within one hour can re-use the previous row store shared memory. After one hour the shared memory is released and a subsequent restart has to recreate the row store memory from scratch.

2 - reuse_shared_memory_for_restart_timeout

Parameter Name     - reuse_shared_memory_for_restart_timeout
HANA Release        - SPS09 and higher
Default Value          - 0 (no timeout)
About Parameter    - This parameter sets the number of seconds the row store information is stored in shared memory after shutdown.

How to Set Parameter - indexserver.ini -> [row_engine] -> reuse_shared_memory_for_restart_timeout

This parameter can be used to define the number of seconds the row store shared memory is kept after a shutdown. The default is 0, which disables the timeout. This parameter is deprecated as of SPS 09. If it is explicitly set on SPS 09 and higher, it is still considered (keep_shared_memory_over_restart_timeout has precedence if explicitly set at the same time), but it is recommended to use it no longer with SPS 09 and higher and instead switch to keep_shared_memory_over_restart_timeout.

3 - reuse_shared_memory_for_restart

Parameter Name    - reuse_shared_memory_for_restart
HANA Release       - SPS07-08 (deprecated in SPS09 and higher)
Default Value         - false
About Parameter   - Is set to true or false, if true the row store data will stay in shared memory.

How to Set Parameter - indexserver.ini -> [row_engine] -> reuse_shared_memory_for_restart

If set to true, SAP HANA will keep the row store in memory when the technical preconditions are fulfilled. If set to false, the row store is generally recreated from scratch during a startup.This parameter is deprecated as of SPS 09. If it is explicitly set on SPS 09 and higher, it is still considered (keep_shared_memory_over_restart has precedence if explicitly set at the same time), but it is recommended to use it no longer with SPS 09 and higher and instead switch to keep_shared_memory_over_restart.

Note : If you run the following on the OS level ipcs -m to view the shared memory you will see the shared memory will have segments set to DEST status and do not go away, even after the HANA services are stopped (Soft shutdown). The reason for this is because the row store data is still in shared memory so that when your HANA services are restarted it won't have to reload the data.

Related Topic - keep_shared_memory_over_restart