What happens at HANA System Restart after crash

The SAP HANA system restart sequence is a process that efficiently brings the system back to a fully functional state. Here's a breakdown of the steps involved:

Reading Restart Records:

The restart agent of the persistence layer accesses the data volume of each service to read and load the restart record.

Managing Transactions:

The list of open transactions is read into memory.

Row tables are loaded into memory.

Processing Open Transactions:

Open transactions are processed using the redo log.

Transactions that were open when the database was stopped are rolled back.

Changes to committed transactions that were not written to the data area are rolled forward.

Handling Aborted Transactions:

Aborted transactions are identified and rolled back.

Creating Savepoint:

A savepoint is performed, capturing the restored consistent state of the database.

Column tables that are marked for preload, and their attributes, are asynchronously loaded in the background:

The preload parameter is configured in the meta-data of the table. This feature is useful, for example, to make certain tables and columns that are used by important business processes available more quickly.

Column tables and their attributes that were loaded before restart, 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).

In summary, the SAP HANA system restart sequence involves a comprehensive set of steps to ensure a smooth and efficient restoration of the system to a fully operational state, including managing transactions, handling aborted transactions, creating savepoints, and loading tables in a strategic manner.

Note : - 

While reloading column tables significantly accelerates the restoration of the database to a fully operational state, it comes with a trade-off in terms of performance overhead. This feature might not be essential for non-production systems. To manage and optimize this process, consider the following configurations:

Deactivation in indexserver.ini:

You have the option to deactivate the reload feature by adjusting the reload_tables parameter in the sql section of the indexserver.ini file. Setting it to "false" turns off the automatic reloading of column tables.

Parallel Loading Configuration:

Adjusting the tables_preloaded_in_parallel parameter in the parallel section of the indexserver.ini file allows you to configure the number of tables whose attributes are loaded in parallel. This setting not only influences the parallel loading of tables during the reload process but also determines the overall performance impact.