Ibm mq
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This document summarizes IBM MQ basics including messaging, queuing, asynchronous and synchronous messaging, message segmentation, message types, persistent vs non-persistent messages, message descriptors, MQ managers, queues, process definitions, channels, and more. Key points are that MQ uses queuing to enable program-to-program communication by sending and receiving messages without a direct connection. Messages have data and descriptor parts, and can be persistent or non-persistent. MQ managers connect applications to queues using channels and provide message queuing interfaces.
Ibm mq
- 1. IBM MQ Basics Messaging Program-to-program communication by sending and receiving messages to and from the queue without having a logical connection between them. Queuing Programs communicate with each other through queues. There are 2 types of messaging 1. Asynchronous Messaging - the sending program proceeds with its own processing without waiting for the reply of the message. 2. Synchronous Messaging Note : Programmer can’t specify the name of the target application to which the message is sent. Instead, he specifies the target Queue as each queue is associated with a program. A Message has 2 parts – Data & Message Header. Message Header(Message Descriptor) identifies the message(message ID) and contains information(attributes) Common attributes are message type, expiry time, correlation ID, priority and name of the queue for reply. Message Segmenting and Queuing. Segmenting a large message if it does not fit the queue and receiver can get the message in one piece or as multiple segments based on the buffer size. Programmer can even segment the messages and each segment is treated as a separate physical message. Thus several physical messages building one logical message. To reduce network traffic, sometimes many small messages are grouped together and sent to destination. MQ Message Types 1. Datagram – Message containing information, but no response is expected. 2. Request – Message for which a reply is requested. 3. Reply – Reply to a request message 4. Report – A message that describes an event such as occurrence of error or confirmation or arrival or delivery. Persistent vs Non-Persistent Messages Deliveries of persistent messages are assured. They are written into logs to survive system failures. Message Descriptor 1. Version – depends on MQ version and the platform in use. 2. Message ID / Correlation ID - these fields are used to identity a specific request or reply. 3. Persistent/Non-Persistent
- 2. 4. Priority 5. Date and time 6. Expiration Date (when is date is reached, MQGET is called and the message is discarded) 7. Return address – (reply-to-queue or reply-to-queue manager) 8. Format – sender can specify a value which receiver can use to decide whether data conversion is done or not. 9. Sender application and type. 10. Report options and Feedback Code – used for request information like confirmation of delivery 11. Back out Counter 12. Message Segment and Grouping MQ Manager (MQM) Manages queues and message for the application Provided Message Queuing Interface (MQI) for communication between programs. Program A (via MQPUT) — > Remote Queue à CHANNEL à Local Queue à Program B (via MQGET) Program A (via MQPUT) — > Shared Queue à Program B (via MQGET) Queue Manager Clusters MQM’s are joined together in clusters which may run in the same machine or different machine. They maintain a repository that contains the information about all the queue managers and queues in the cluster. (Full Repository) The un-clustered MQM’s manage a repository that contains the information of the objects they are interested in (Partial Repository) MQM uses special cluster channels to exchange information Queue Manager Objects 1. Queues 2. Process Definitions 3. Channels Queues Queues are classified as Local Queue a real queue Remote Queue structure describing a queue Transmission Queue local queue with special purpose Initiation Queue local queue with special purpose Dynamic Queue local queue created on the fly to store intermediate results Alias Queue not real queues but definitions in case you want alias names Dead-letter Queue one for each queue manager to store the messages when handling situations like destination queue is full, dest queue doesn’t exist, message is too large, duplicate message sequence number etc. Reply-to Queue specified in request message
- 3. Model Queue model for local queues Repository Queue holds the cluster information Process Definitions Defines an application to a queue manager. Eg: the name of the program (and its path) to be triggered when a message arrives for it. MQ Channels Channels are classified into Message Channels connects 2 queue managers via Message Channel Agents (MCA or movers) unidirectional Comprises of 2 MCAs, a sender and a receiver and a communication protocol. MCA is a program that transfers messages from transmission queue to communication link and vice versa MQI Channels Message Queue Interface channel Connects MQ client to a MQM in the server machine. Bi-directional.