SAP HANA Database restart/startup sequence

 SAP HANA system restart/startup sequence.

When the SAP HANA system restart sequence restores the system to a fully operational state quickly.

 1.The data volume of each service is accessed in order to read and load the restart record.

 2. The list of open transactions is read into memory.

 3. The row tables are loaded into memory. 

4. Open transactions are processed using the redo log, as follows: 

1. Write transactions that were open when the database was stopped are rolled back.
2.  Changes of committed transactions that were not written to the data area are rolled forward. The first column tables are reloaded into memory because they are accessed for roll forward. 
3. After this step, the database is technically available and logon is possible. 

5. Aborted transactions are determined and rolled back. 

6. A save point is performed with the restored consistent state of the database. At this point the database is restored from the persistence layer’s point of view. The column store can now load the tables marked for preload into memory. 

7. Column tables, which are marked for preload, and their attributes are asynchronously loaded in the background, if they have not already been loaded as part of log replay.

The preload parameter is configured in the metadata of the table. This feature makes certain tables and columns that were used by important business processes available more quickly. 

8. Column tables that were loaded before restart, and their attributes, start reloading asynchronously in the background, if they have not already been loaded as part of log replay or because they are marked for preload. During normal operation, the system tracks the tables currently in use. This list is used as basis for reloading tables after a restart. 

 

Note : When SAP HANA  system restart, by default, not all tables are loaded into the main memory immediately. 

Content reference from HA200 Study materiel.