Message Queue Interview Questions

What is MQ and what does it do?

MQ stands for MESSAGE QUEUEING. WebSphere MQ allows application programs to use message queuing to participate in message-driven processing. Application programs can communicate across different platforms by using the appropriate message queuing software products.

What is Transmission Queue?

Transmission queues are queues that temporarily store messages that are destined for a remote queue manager. You must define at least one transmission queue for each remote queue manager to which the local queue manager is to send messages directly.

What is Initiation Queues?

Initiation queues are queues that are used in triggering. A queue manager puts a trigger message on an initiation queue when a trigger event occurs. A trigger event is a logical combination of conditions that is detected by a queue manager.

What is Dead Letter Queue?

A dead-letter (undelivered-message) queue is a queue that stores messages that cannot be routed to their correct destinations. This occurs when, for example, the destination queue is full. The supplied dead-letter queue is called SYSTEM.DEAD.LETTER.QUEUE. For distributed queuing, define a dead-letter queue on each queue manager involved.

What is Process Definition and what are the attributes does it contain?

A process definition object defines an application that starts in response to a trigger event on a WebSphere MQ queue manager. The process definition attributes include the application ID, the application type, and data specific to the application.

What is channel and mention different types of channels in MQ?

Channels are objects that provide a communication path from one queue manager to another. Channels are used in distributed queuing to move messages from one queue manager to another. They shield applications from the underlying communications protocols. The queue managers might exist on the same, or different, platforms. Different types of Channels:

• Sender-Receiver Channels
• Requester-Server Channels
• Client Connection channels
• Server Connection Channels.
• Cluster Sender.
• Cluster Receiver Channels

What is Cluster?

A cluster is a group of queue managers set up in such a way that the queue managers can communicate directly with one another over a single network, without the need for transmission queue, channel, and remote queue definitions.

What is Message driven process?

When messages arrive on a queue, they can automatically start an application using triggering. If necessary, the applications can be stopped when the message (or messages) have been processed.

What are advantages of the MQ?

• Integration
• Asynchrony
• Assured Delivery
• Scalability

How does it support the Integration?

Because the MQ is independent of the Operating System you use i.e. it may be Windows, Solaris,AIX.It is independent of the protocol (i.e. TCP/IP, LU6.2, SNA, NetBIOS, UDP).It is not required that both the sender and receiver should be running on the same platform

What is Asynchrony?

With message queuing, the exchange of messages between the sending and receiving programs is independent of time. This means that the sending and receiving application programs are decoupled; the sender can continue processing without having to wait for the receiver to acknowledge receipt of the message. The target application does not even have to be running when the message is sent. It can retrieve the message after it is has been started.

What is a Message and what does it contain?

A message is a string of bytes that is meaningful to the applications that use it. Messages are used to transfer information from one application program to another (or between different parts of the same application). The applications can be running on the same platform, or on different platforms. WebSphere MQ messages have two parts:

• The application data. The content and structure of the application data is defined by the application programs that use it.
• A message descriptor. The message descriptor identifies the message and contains additional control information, such as the type of message and the priority assigned to the message by the sending application. WebSphere MQ defines the format of the message descriptor.

What is the Max Length of the message does MQ support?

The default maximum message length is 4 MB, although you can increase this to a maximum length of 100 MB (where 1 MB equals 1 048 576 bytes).

What is Queue?

A queue is a data structure used to store messages. A queue manager owns each queue. The queue manager is responsible for maintaining the queues it owns, and for storing all the messages it receives onto the appropriate queues

What are the Different Types Of Queues?

Queues can be characterized by the way they are created:

• Predefined queues are created by an administrator using the appropriate MQSC or PCF commands. Predefined queues are permanent; they exist independently of the applications that use them and survive Web Sphere MQ restarts.
• Dynamic queues are created when an application issues an MQOPEN request specifying the name of a model queue. The queue created is based on a template queue definition, which is called a model queue.

How does an application sends and receives messages from the Queues?

Application programs send and receive messages using MQI calls.

• MQOPEN: It is used to open the Require Queue.
• MQPUT: It is used to PUT the message in to the Required Queue.
• MQGET: It is used to get the message from the required Queue.
• MQCONNX: This command used to connect to the QueueManager
• MQPUT1: It performs the putting, browsing and getting application at a time on a single queue.
• MQCLOSE: It closes the connection with the Queue.
• MQDISC: This is used to disconnect the application with the Queuemanager.