Top 10 MQ Series Interview Questions Answers - WebSphere and Active MQ

MQ Series Interview Questions and Answers are collections of some of the questions asked on various MQ implementations e.g. IBM WebSphere MQ, Active MQ or Sonic MQ from different core Java and Enterprise Java (JEE) interviews. Most of these questions are from WebSphere MQ as it's the one that is most popular in large organizations, especially in the finance domain. By the way messaging is a key aspect of any enterprise application and you will always see some form of messaging between different systems in an organization. For example, In the finance world, most of the middle office to back office communication happens over messaging middle-ware like TIBCO or MQ Series. 

It's one of the popular Message Oriented Middleware used in Core Java and Enterprise Java application deployed on IBM WebSphere Server, which means if your organization is using IBM WebSphere as an application server, you are likely to see WebSphere MQ there.


By the way that's not the only messaging solution available, you have a couple of choices depending upon requirement e.g. Tibco Rendezvous for high speed messaging, Tibco EMS for a JMS-based messaging, mostly for durable messages, and MQ series as well.

It's a long time I have written an article on messaging after my articles based on Tibco messaging, along with some Tibco Interview Questions e.g. difference between Tibco RV and Tibco EMS.

In this messaging article, the focus will on MQ Series and in particular WebSphere MQ. These 10 WebSphere MQ interview Question and Answers will certainly help you to prepare better for any Java interview which expects an experience on MQ Series.

MQ Series Interview Questions Answers

Here is my collection of interview question based upon basic concepts of MQ series. Though you may expect some general messaging questions as well as some JMS based question on Java interviews, be ready for MQ series question if Job description has any word related to MQ e.g. WebSphere MQ or Active MQ.

Most of the questions are based upon practical knowledge but they are essentially fundamentals and if you know them, you can do very well in Java JEE interviews. In fact those who are particularly giving interview for support roles, knowledge of WebSphere MQ is really valuable.

If you worked on Tibco RV or WMQ then always mention it on your CV, its a very sought after skill set on financial organization. These questions are good to refresh your memory before going for personal or telephonic interviews.

1. What is QueueManager in IBM WebSphere MQ? What does QueueManager do?
QueueManager is a primary component of WebSphere MQ or WMQ. QueueManager is responsible for storing and routing messages to other Queue Manager within MQ and it also communicate with outside world e.g. Java program or any other MQ client.

2. What is Channel in IBM WebSphere MQ?
In WebSphere MQ or WMQ, Queue Manager use the channel to transmit messages to other QueueManager. Channel carries one way traffic in MQ Series (i.e. channels are uni directional). You can have either sending channel or receiving channel in MQ.

3. What is dead letter queue in IBM MQ Series ?
Dead letter Queue in WebSphere MQ is a queue which is used by QueueManager to archive messages for a non existent queue. For example of QueueManager QMGR, receives a messages for queue ABC and if it didn't exist on that QueueMangaer then message will be routed to dead letter queue.

4. What is the CCDT file on WebSphere MQ or WMQ?
CCDT file or Client Channel Definition table is a binary file that contains connection details required by MQ clients e.g. Java application using JMS to connect to MQ Server. In order to connect to MQ Server, MQ clients need MQ Server hostname, MQ Server port name, and server channel name. All these details are encapsulated in the CCDT file named AMQCLCHL.TAB. In order to create MQ Connection, MQ clients need the location of this file, which is provided as a configuration. most MQ errors come either with incorrect CCDT files.

5. What is SSLPEER in IBM Websphere MQ?
Another interesting and frequently asked WebSphere MQ Interview Question. You can easily answer this MQ question if you connected MQ via SSL. SSLPEER is a String usually DN (Distinguished Name) of MQ Client which connects to QueueManager securely using QueueManager. This is a mechanism WMQ uses to identify clients. In the case of Java or JMS clients, SSLPEER is DN of client certificate stored in its keyStore and sent to the server during SSL handshake.

6. What is the difference between dead letter queue and backout queue in Websphere MQ ?
This is a follow question of previous MQ interview question "What is dead letter queue in MQ Series". As we have seen that dead letter queue is used to store messages which is receives for non existent queue. On the other hand backout queue are application specific queue.If MQ client is not able to process message and ask for redelivery, message is redelivered to client with incremented delivery count. Once this deliveryCount crossed a configured threshold message is moved to back-out queue for later processing or error handling. In short if MQ Series not able to deliver message to client after a preconfigured attempt, WMQ moves message to backout queue.

7. What is difference between binding connection and client Connection ?
This MQ Interview question is not common or frequently asked, but good to know. If MQ clients sits on same physical server where QueueManager is located than it can create binding connection which is relatively faster than client connection, which is usually created by MQ clients residing on same network but not same host. Most of application uses MQ client connection to connect QueueMangaer, which is easy and flexible.

8. What is the difference between a local queue and a remote queue in WMQ?
Rather simple and fact-based MQ Series interview question. This is asked to see whether candidate is familiar with MQ Series terminology or not. In WebSphere MQ, local queues are queue on same QueueManager while remote queue refers to queues on different QueueManager.

9. Which WebSphere MQ version have you worked on? What is the latest IBM WebSphere MQ version?
This MQ interview question is more to know that which version of MQ have you worked upon, do you are familiar with any issue with that particular version or many major changes to previous or next version, etc. Based upon your answer, you may expect some follow-up questions. By the way current version of WMQ is WebSphere MQ 7.5 but it is always good to check IBM's MQ website for the latest version.

10. Apart from WebSphere MQ, have you used any other Message Oriented Middleware (MOM) or any other MQ Series provider?
I like this MQ Interview question to ask because many times having experience of one or more Messaging technology or Messaging Middle-ware is good. As I said earlier Tibco RV, Tibco EMS and MQ Series are some of the popular messaging technology used in Java applications. 

On the MQ front, there are a couple of more MQ providers like Sonic MQ and Active MQ. Active MQ is free and from Apache software foundation, which is easy to install and use. You can use Active MQ for your development and test environment. it also provides a useful Queue browser to keep track of Queues and number of message on it.

That's all on this list of websphere mq series questions and answers. If you have faced any other interesting MQ Series Interview question on WebSphere MQ, Sonic MQ or any other open source MQ provider e.g. Rabbit MQ than feel free to share with us. You can also shared MQ related questions for which you don't know answers.