Index server contains SQL/MDX processor to handle query statements for the database. When SQL or MDX is fired for SAP HANA system, an Index Server takes care of all these requests and processes them. All HANA processing takes place in Index Server.
Index Server contains Data engines to handle all SQL/MDX statements that come to HANA database system. It also has Persistence Layer that is responsible for durability of HANA system and ensures HANA system is restored to most recent state when there is a restart of system failure.
Index Server also has Session and Transaction Manager, which manage transactions and keep track of all running and closed transactions.
You can check different details about Index server- Used memory, Peak used memory, and allocation limit, etc.
Select HANA system in HANA studio and navigate to Administration tab
To check the configuration of Index server, you can also check different parameters under Index server.ini file.