Mainframe Interview Questions

Primary key : a relational database constraint. Primary key consists of one or more columns that uniquely identify a row in the table. For a normalized relation, there is one designated primary key.

Unique index: a physical object that stores only unique values. There can be one or more unique indexes on a table.

If any one want to restrict Trans-ID to single user, enter trans-id with ENQ. It won't allow any one else to use the same trans-id.

They communicate via service MVS request calls.

The INTO option moves the information in the TIOA into the reserved specified area, while the SET option simply returns the address of the TIOA to the specified BLL cell or address of a linkage-section.

PCT (Program Control Table) - Defines each transaction containing a list of valid transaction identifiers (transid) where each transaction is paired with its matching program.

PPT (Program Processing Table) - Contains a list of valid program names and maps and whether a current version is in the CICS region or needs to be brought in as a new copy.

FCT (File Control Table) - Contains a list of files known to CICS, the dataset name and status (closed/open, enable/disabled)

TCT (Terminal Control Table)- A list of the terminals known to CICS.

The simplest DB2 index is the B-tree and the B-tree's top page is called the root page. The root page entries represent the upper range limits of the index and are referenced first in a search. 

DB2 use the multiple indexes to satisfy multiple predicates in a SELECT statement that are joined by an AND or OR.

The following commands are available for the Program Control services:

LINK: To pass control to another program at the lower level, expecting to be returned. XCTL: To pass control to another program at the same level, not expecting to be returned.

RETURN:  To return to the next higher-level program or CICS. 

LOAD: To load a program. 

RELEASE: To release a program.