IMS DB Realtime (Scenario based) Interview Questions (11 - 20)
11. What is database shadowing?
Database shadowing is like having a real-time backup of your IMS database. Whenever data changes in the main database, the same change is automatically applied to the shadow (copy) database. It ensures quick recovery if the main database fails.
12. What is PSB MASK?
A PSB MASK is a filter that restricts which parts of the database a program can access, even if the PSB (Program Specification Block) allows more. It is used for security or to limit unnecessary data access. For example - If a PSB allows access to CUSTOMER and ORDER data, a MASK can block ORDER access.
13. What is a path call?
A path call retrieves multiple segments in a single I/O operation by following the database hierarchy. For example - GET PATH can fetch COMPANY → DEPARTMENT → EMPLOYEE at once.
14. What is multi-positioning?
Multi-positioning allows a program to remember multiple locations in the database at the same time. It helps when working with different segments without losing track. For example - A program can hold a position in both CUSTOMER and ORDER segments.
15. Define a search field.
A search field is a key field used to find a specific segment in IMS. It is used in SSAs (Segment Search Arguments) like STUDENT(STUDENT_ID='1001'). For example - In a STUDENT segment, STUDENT_ID could be the search field.
16. What is GA status code?
GA is a status code returned by IMS when a requested segment is not found. Programs should check for GA to handle missing data. For example - If you search for EMPLOYEE(ID='999') but it doesn’t exist, IMS returns GA.
17. Explain DL/I log.
The DL/I log (Data Language/I log) is a record of all database changes (inserts, updates, deletes). It helps recover the database in case of failure. For example - Like a "black box" in an airplane—it keeps track of everything that happens.
18. What is the difference between a full-function PCB and a fast-path PCB in IMS DB?
| Full-Function PCB | Fast-Path PCB |
|---|---|
| Used for standard IMS databases (HDAM, HISAM, etc.). | Used for high-speed Fast Path databases (DEDB, MSDB). |
| Supports all DL/I calls (GU, GN, ISRT, etc.). | Optimized for fast access, fewer features. |
| Good for general-purpose applications. | Best for real-time, high-volume transactions (e.g., ATMs). |
19. What is the limitation on the number of levels in a DL/I database?
In IMS DB, a DL/I database can have up to 15 levels in its hierarchy. This limit ensures efficient data traversal and storage. For example - ROOT → Level1 → Level2 → ... → Level15
20. How many segment types can you have in a DL/I database?
A DL/I database can have up to 255 segment types (different kinds of records). Each segment type can have multiple occurrences (actual records). For example - A SCHOOL database may have segments like STUDENT, TEACHER, CLASS, etc.