Star topology of SAP Systems

I have found that not many SAP admins notice that SAP system architecture resembles a star topology and that this was a conscious decision on SAP's part.

If there is any confusion on realising this--the central services instance forms the central node of a star topology and the individual instances are the connected nodes.

The biggest advantages of this topology are:
1. Central hub controls and communicates with rest of the nodes through client-server connectivity, keeping track of load levels, availability and non-duplication of changes.
2. The network connections grow linearly with the number of nodes added, as opposed to exponential growth with other topologies. This not only reduces cost, but also complexity.

The major disadvantage is that the loss of the central node will cause the entire system to go down. This is where High Availability comes to play.

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Taking a Full Webpage Screenshot using Firefox

If you need to take a screenshot of the entire webpage, you can use Firefox's built in command line feature to achieve it.

Press Shift + F2, a command line prompt will appear at the bottom-left part of the browser window.
Type screenshot --fullpage and press enter. The page will be saved in your default download location.

There are other options available on the command line which can be looked up using the command help

Firefox Shift F2 Command Line Help

HANA Alert 'Check whether the database is running in log mode overwrite'

HANA system triggers regular save points which are backed up in case of a database recovery. In order to recover the database at a point-in-time, logs must be recorded between the save points. If such recording in disabled (for example to prevent file system growth), the alert 'Check whether the database is running in log mode overwrite' is triggered.

The log mode must be normal in a productive environment.

To fix this alert, call HANA studio --> Configuration --> global.ini --> persistence and set the parameter log_mode to normal.

Reducing memory usage of HANA DB caused by table preload

HANA database periodically keeps track of the column attributes loaded in to the memory during a normal operation. This information is stored as table preload information, which in turn is used to load the column attributes back after each restart of the index server. This results in improvement of query execution, but it also causes the memory usage to go up.

Use the following procedure to reduce the memory usage:
  1. Deactivate the preload feature of the index server temporarily by setting the reload_tables parameter in the sql section to false
  2. Deactivate the collection of table preload information in the indexserver.ini file by adding the parameter tablepreload_write_interval in the persistence section and setting the value to 0
  3. Restart SAP HANA
  4. Execute frequently used queries to load corresponding column table attributes into memory.
  5. Manually store the above information to be used for the next restart by excuting the command hdbcons "tablepreload writeinfo"
  6. Re-activate the preload feature in the indexserver.ini file by setting the reload_tables parameter in the sql section to true. The stored table preload information will be used at the next restart.