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If you are here looking for help to prepare for your next Mainframe interview, you are at the right place. Below are the top 20 Mainframe interview questions that are most commonly asked in Mainframe interview.
1. What is DRDA?
DRDA stands for Distributed Relational Database Architecture. It works as a connection protocol for local database processing. Database vendors like IBM use it. This architecture contains a set of rules that helps communicate between any application and database relation.
2. What is the function of the clause WHERE in mainframe programming?
While working with a relational database system, the clause “WHERE” isolates an element or a row.
3. Explain how the LIKE table can be created?
You can use the LIKE parameter and the CREATE statement to create the LIKE table. These tables are needed during the testing phase of the production environment.
4. How is runstats used in environment testing?
The catalog columns are filled with default values and the end result during environment testing may not produce accurate results. Runstats is used to clear the default values of these columns.
5. Explain the function of Linkage Area in COBOL
If a COBOL program needs to speak with a JCL or another program through the PARM parameter, Linkage Area is used.
6. What is a COPYBOOK in COBOL?
COPYBOOK stores the format of any record and uses the same design for another program. We can use the same COPYBOOK for a number of documents using the REPLACING choice if the format is the same.
7. Differentiate between INCLUDE and COPY
INCLUDE and COPY are different in the way they work. They are used for extension of design in a program. The main difference is that INCLUDE is used for expanding at a pre-compiler time whereas COPY is used for expanding at a compiler time.
8. What are Foreign Keys?
Foreign keys are attributes of a particular table that have matching entries to the primary key in another table. Foreign keys are used to build a relation between any two tables.
9. What do you mean by self-referencing constraint?
Self-referencing constraint is used to restrict the changes that can be made to the primary key through a foreign key. To implement this, the foreign key must define the DELETE CASCADE rule.
10. What is meant by deadlock in DB2?
When two separate processes are fighting for the same resources, or the resource reserved for each other, the situation is called a deadlock. SQL code for a deadlock are -911 and -913.
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11. Differentiate between Type 1 and Type 2 indexes
In Type 2 index, the data pages get locked but index pages are not locked. In Type 1 index, the index pages are locked. Type 2 index is quicker than Type 1 index.
12. Name the different Table spaces
The three Table spaces are Simple, Segmented and Partitioned Table spaces.
13. How are HIDAM and HDAM databases different?
HIDAM has its separate index file based on the root segment. This file stores information about the pointer that denotes the position of data. Whereas, HDAM does not have a separate index file. The key field of each record is accessed through a randomizer that positions the record in the correct place in the database.
14. What is referential integrity?
Referential integrity rule states that consistency needs to be maintained between primary and foreign keys. In other words, each foreign key needs to have a primary key.
15. What is the difference between multiple index and composite index?
Multiple indexes consist of 2 indexes, one for each table column. The composite index is just one index that consists of joint values of 2 columns of the table.
16. What are the differences between GOBACK, STOPRUN and EXIT PROGRAM in COBOL?
The main differences between GOBACK, STOPRUN and EXIT PROGRAM in COBOL are:
GOBACK gives control back to the calling program.
STOPRUN stops current work execution to return control to the operating system.
EXIT PROGRAM is used to quit a program and allow another program to pursue.
17. What is the benefit of De-normalizing tables in DB 2?
Denormalizing reduces the necessity of executing various relational joins. It also reduces the requirement of foreign keys.
18. Explain Database Descriptor
Database Descriptor or DBD provides restricted access to the database when an object gets created, altered or dropped.
19. Explain delete-connected tables
Tables whose relation is established through a foreign key are called delete-connected tables. Whenever a primary key is deleted, the foreign key in the corresponding table is also impacted.
20. What are the different types of Locks?
There are mainly three types of locks. They are:
Shared Lock- This type of lock allows more than one program to read from locked part but not change it.
Update Lock- This lock allows the program to both read and change the data in the locked area.
Exclusive Lock- This Lock is restricted and does not allow any program to even access the locked space.
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