Introduction to WebSphere MQ

1. Middleware

Middleware is between application software and system software, and it is a reusable basic software which can be used to simplify the enterprise application. Before the production of middleware, the application software directly using the operating system, network protocols and database development, developers have to face a lot of difficult problems, such as the diversity of operating systems, complex network design and management, the complexity of the network environment, data dispersion processing caused by inconsistencies, performance and efficiency, security issues and so on. These problems are not directly related to the user's business, but must be resolved, consuming a lot of limited time and effort. Therefore, it is proposed that the application software to face the common problems of refining, abstraction, on the operating system to form a reusable part, for thousands of application software reuse. This technical thought eventually formed for middleware products.

Technically speaking, middleware is a kind of software between application system and system software, which uses the basic service (function) provided by the system software, connects the various parts of the application system on the network or different applications, and can achieve the purpose of sharing resources and sharing functions.

2.Websphere MQ principle

Websphere MQ is IBM's commercial communications middleware (commercial Messaging middleware). Websphere MQ provides an industry-standard, secure, and reliable messaging system. Its function is to control and manage an integrated business application, making it possible to complete the workflow by passing messages between multiple branch programs (modules) that make up this commercial application. Websphere MQ is basically comprised of a message transfer system and an application interface whose resources are messages and queues (Messaging and Queuing).

message : A message is a unit of information that can be either a request message or an answer (Reply message) or a report message or a message ( Datagram messge). A message contains two factors-a message description (used to define such as a message transmission target, etc.) and a data message (such as application data or database queries). Communication between programs is done by passing a message instead of calling the program directly.

queues: a secure place to store messages, where messages are stored in sequential order, and queues are transmitted and received in stages by messages. Because messages are stored in queues, applications can run independently of each other at different speeds, at different times, at different locations.

message transfer system: used to ensure the delivery of messages between queues, including the delivery of messages between remote queues on different systems in the network. and ensure a network failure or recovery after shutdown.

Application Interface: The WebSphere MQ API is consistent across all WebSphere MQ platforms for interfaces between applications and messaging systems through the WebSphere MQ API. The API has only 14 calls, 2 key verbs: Send (PUT) and receive (GET).

: Although application A and application B run on the same system A, they do not require direct communication. Application A sends a message to queue 1, and the message is available when application B needs it.

If the destination of the message transfer is changed to Application C on system B, this change does not affect application A, application A sends a message to the queue Q2, and WebSphere MQ of system A discovers that Q2 is actually in System B, which places the message on a special queue locally-the transmission queue ( Transmission Queue). WebSphere MQ for System A then establishes a communication connection to system B, passing this message to system B and waiting for confirmation. Only WebSphere MQ will be removed from the transmission queue after it has received confirmation from System B to successfully receive the message. If the communication line is not available, or system B is not running, the message remains in the transmission queue until it is successfully delivered to the destination. This is the most basic and most important technology for WebSphere MQ-reliable message transmission. In fact, Websphere MQ has special techniques to prevent message recurrence, ensuring that messages are delivered once and only once (once-and-only-once).

Introduction to WebSphere MQ