DB2 Interview Questions and Answers

Concurrency in an environment or ability where multiple applications can have access to the same data at the same time.  However, Concurrency has been designed in a way to prevent problems during multiple applications accessing the same data. The common problems that arise during the concurrency execution are uncommon data, lost data, and unrepeatable reads. The DB2 uses one of the basic ways to control concurrency through units of locking. When a unit is locked it is still in locking mode till the work is completed and then it is released back to normal.  

DBRM is abbreviated as a Database Request Module and it is one of the major components resided inside DB2. DBRM contains SQL source statements that can be easily extracted from the application program. It generates inputs that play a key role in executing the binding process.  

RCT is abbreviated as a Resource Control Table and resides in the DB2/CICS region. All the features of RCT are collected through macros of DSNCRCT. 

The buffer manager is a major component that resides inside DB2 and acts as a medium for data transfer between virtual as well as the external medium. The buffer manager has the capability to bring down the number of physical inputs and output operations by using various highly sophisticated buffering techniques.  

PACKAGES play an important role in DB2 and act as a place for control structures. DB2 uses packages to control structures while executing SQL statements. Packages are created during program preparation. 

Below mentioned are the advantages of Packages: 

• It eliminates all the unnecessary stuff and gives you small collections and saves you cost. 
• Makes the process simple by eliminating the need to bring a large number of members of DBRM together for a specific plan. 
• The programmatic changes and errors associated with them can be minimized by using Packages. 
• When the process of automatic binding or rebinding takes place for a specific plan, Packages ensure that the entire transaction attracted to the process remains in isolation or unavailable. 

The major purpose of using DCLGEN is to detect the misspelt column names during the precompilation process. There is no such mandate to use the DCLGEN. It is a common tool that helps in generating variable definitions for hosts and minimizes the chance of occurring errors. 

The EXPLAIN statement gathers and stores the data about access path selection that is useful for an explainable statement. A statement is considered as an explainable one if it is a MERGE, SELECT, or INSERT statement, or searched form of DELETE or UPDATE statement. The information obtained will be stored in a supplied set of user tables and these tables are called EXPLAIN tables. 

A DB2 unit is a list of recoverable series of tasks or operations executed by DB2 for executing an application. There is always coordination between the units of recovery and works together in a process to make changes to other recoverable resources. If an application process is using a relational database as their single most recoverable resource, then the scope of the unit of recovery and unit of recovery are the same. 

DB2 manages a list of tables that consists of data about the information that can be controlled by DB2. All these tables together are called a catalogue. These catalogue tables hold information about DB2 objects which include views, tables, and indexes. Whenever you alter, create, or drop an object the DB2 updates, inserts, or deletes rows of the catalogue.  A DB2 catalogue consists of complete data about each aspect defined in the DB2 system which includes indexes, tablespaces, copies of indexes and tablespaces, and storage groups.