Mainframe Interview Questions

While allocating KSDS Datasets, free space is declared at regular intervals at the time of initial loading. This is done because this free space is utilized for keeping the data arranged in sequence physically, even though inserted randomly.

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.

Customer Information Control System (CICS) is an online transaction processing monitor from IBM that acts as an interface between the operating system and application programs to provide rapid high-volume online transaction processing.

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.

GROUP BY partitions the selected rows on the distinct values of the column on which you group by. HAVING selects GROUPs which match the criteria specified

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. 

Syntax:

SORT   file-1 ON ASCENDING/DESCENDING KEY key....

USING  file-2

GIVING file-3.

USING can be substituted by INPUT PROCEDURE IS para-1 THRU para-2

GIVING can be substituted by OUTPUT PROCEDURE IS para-1 THRU para-2.

file-1 is the sort workfile and must be described using SD entry in FILE SECTION.

file-2 is the input file for the SORT and must be described using an FD entry in FILE SECTION and SELECT clause in FILE CONTROL.

file-3 is the outfile from the SORT and must be described using an FD entry in FILE SECTION and SELECT clause in FILE CONTROL.

file-1, file-2 & file-3 should not be opened explicitly.

INPUT PROCEDURE is executed before the sort and records must be RELEASEd to the sort work file from the input procedure.

OUTPUT PROCEDURE is executed after all records have been sorted. Records from the sort work file must be RETURNed one at a time to the output procedure.

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