IBM MQ Series For ZOS
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IBM MQ (formerly known as MQSeries) is middleware that implements message queuing using queues to allow programs to communicate asynchronously. It runs on many platforms and supports transactional message passing between programs. Key objects in MQ include queue managers, queues, channels, and messages. Messages are placed on queues and can be retrieved later, even if the sending program has ended. MQ uses logging and recovery to ensure reliable message delivery even if failures occur. It provides benefits like loose coupling between applications, assured delivery through persistence, and ability to integrate with transactional systems.
IBM MQ Series For ZOS
- 1. W W W. S R I N I M F. CO M Copyright 2014 IBM MQ FOR ZOS
- 2. Basics Copyright 2014 MQ Series is a middleware software that implements messaging and queuing. Messaging - - programs communicate by sending data in messages rather than by calling each other directly. Queuing - messages are put on queues in storage, eliminating the need for programs to be logically connected.
- 3. Details Copyright 2014 Initially, IBM’s version of MQSeries ran only on mainframe (CICS/ESA, IMS/ESA, and eventually VSE). Today it runs more than 35 platforms
- 4. MQ Series Objects Copyright 2014 Queue Manager A queue manager is that part of an MQSeries product that provides the messaging and queuing services to application programs, through the Message Queue Interface (MQI) program calls. It controls access to queues and serves as transaction (syncpoint) coordinator for all queue operations.
- 5. QUEUES Copyright 2014 MQSeries defines four types of queues. A queue instance is fully qualified by its queue manager and queue name. Local Queue - an actual queue for which storage is allocated. Remote Queue - a definition of a queue on a different queue manager (acts somewhat like a pointer) Alias Queue - another name for a local or remote queue. Typically used to switch queue destinations without modifying program code Model Queue - a template whose properties are copied when creating a new dynamic local queue (“ create queue xxx “like” queue yyy).
- 6. Triggers And Local Queues Copyright 2014 Local queues can generate events (messages) under certain conditions (like queue full). These “event” messages can be used to “trigger” the execution of a program. These events are called trigger messages. The queue on which they are put is called an Initiation Queue.
- 7. Trigger Monitor Copyright 2014 Process defines an application to an MQSeries queue manager. A process definition object is used for defining applications to be started by a trigger monitor. A trigger monitor is a program that listens on an initiation queue and executes commands named in Process definitions
- 8. Tip Copyright 2014 Both CICS and MQSeries were developed at Hursley Laboratory in the United Kingdom
- 9. Channels Copyright 2014 A channel provides a communication path between Queue Managers. There are two types of channels - Message Channels and MQI channels (also called Client channels). Message channels - provide a communication path between two queue managers on the same, or different, platforms. A message channel can transmit messages in one direction only. If two-way communication is required between two queue managers, two message channels are required.
- 10. Channel Types Copyright 2014 There are six types of message channels: Sender - initiates connection to Receiver Server - Accepts request to start from requester, then becomes Sender Receiver - Passive; waits for initiation sequence form Sender Requester - Active at start, then becomes Receiver Cluster-sender (used amongst Cluster Queue Managers) Cluster-receiver –As above The Sender side of the session is the “transaction coordinator”. Message channels implement a protocol that includes a commitment protocol. Channels recover from failure by agreement: they must agree on the last committed unit of work .(This is the reason channels are oneway)
- 11. MQI Channels Copyright 2014 MQI channels - connect an MQSeries client to a queue manager on a server machine (where a queue manager is defined). Used for transfer of MQI calls and responses only and is bi-directional.
- 12. Flow of Messages Copyright 2014
- 13. Flow of Messages Copyright 2014
- 14. Details-Flow Copyright 2014 1. Transmission Queue is a local queue. 2. Remote Queues “name” a transmission queue, and a remote Queue Manager (QM2) and q local queue on QM2 3. App opens queue that is defined as a remote queue 4. App puts to queue 5. Queue manager places message on transmission queue 6. Message Channel Agent reads message and sends to remote MCA. 7. Remote MCA gives message to Queue Manager QM1 8. QM1 puts message to target queue.
- 15. Messages Copyright 2014 A message any arbitrary data that one program wants to send to another. This data is called the application data. A message needs to include other information, such as its destination and possibly a return address. This type of data is called the message descriptor
- 16. Messages Copyright 2014 A message any arbitrary data that one program wants to send to another. This data is called the application data. A message needs to include other information, such as its destination and possibly a return address. This type of data is called the message descriptor. There are four types of messages: A request message is used by one program to ask another program for something (usually data). A request message needs a reply.
- 17. Messages contd… Copyright 2014 A reply message is used in response to a request message. A one-way message, as you would expect, doesn’t need a reply, though it can carry data. A report message is used when something unexpected occurs. For example, if the data in a reply message is not usable, the receiving program might issue a report message.
- 18. Message Contd… Copyright 2014 Most useful report messages are generated by the Queue Manager. For example, Delivery confirmation. Messages can have a “time-to-live”, called Expiry. A message that has not been delivered before its expiration is removed (not given to an app) What to do with undeliverable messages? Each queue manager can have a dead-letter queue.
- 19. Messages Contd… Copyright 2014 Messages can be individually designated persistent or non-persistent (persistent messages are logged to enable recovery) Message Correlater - select which message to get from queue Message Priority - retrieve messages in different order of put Segmented Messages - allows ending of VERY LARGE messages (> 100 MB). A message can contain a “reply to” address (the name of a Queue Manager and Queue). This tells the receiving application where any response should be sent. Messages are added and removed from queues in Units of Work. The smallest Unit of Work is one message. Units of work are atomic. When an app reads a message from a queue, a message “appears” to have been removed, but in fact, it is still in storage until the app “commits” the unit of work.
- 20. Transaction Support Copyright 2014 Unit of recovery - a piece of work that changes data from one point of consistency to another. Syncpoint - A point of consistency (also called a or commit point). It is a moment at which all the recoverable data that an application program accesses is consistent.
- 22. Process contd… Copyright 2014 Applications are responsible for delimiting the beginning and end of a transaction. How can messaging be coordinated with a data base update? MQSeries is XA compliant and can operate with other XA compliant systems as either a transaction manager (coordinator) or resource manager (particpant). Some examples: Sybase, DB2, Oracle.
- 23. MQ Series Logging Copyright 2014 All operations that affect the “state” of the Queue Manager and its objects are logged to a log file. What is “state”? Object definitions (queue manager, queues, processes, channels, etc) Queue content (messages) What about message channel state? Message channel states are logged separately by each channel.
- 24. Logging and Recovery Copyright 2014 Circular – log records are written sequentially across several files, then “wrap” back to the first file. Linear - log records are written sequentially across files. New files are allocated as current files fill. No automatic reuse of file space! Problem: Length (in time) of longest running transaction vs amount of writes to log determines size of log needed.
- 25. Tips… Copyright 2014 Circular logging is easy to manage, but is fatal if log is damaged (hard to backup circular logs!). Linear logging is hard to maintain but provides for archiving of previous logs (still a problem if “current” log is damaged).
- 26. MQ Interfaces Copyright 2014 MQCONN – Connect to queue manager MQDISC – Disconnect from queue manager MQOPEN – Open object MQCLOSE – Close object MQPUT – Put message MQPUT1 – Put one message MQGET – Get message MQBEGIN – Begin unit of work MQCMIT – Commit MQBACK – Back out MQINQ – Inquire about object attributes MQSET – Set object attributes
- 27. Benefits Copyright 2014 Interoperabilty - across dissimilar networks between different computing environments Asynchrony - Eliminates the time dependency between applications (both apps must be alive AND have a session in synchronous models). Fewer Network Sessions - Only Queue Mangers need to communicate using network sessions. Administered Objects - Improves manageability of BIG systems -Can monitor the state of a queue to determine if apps are doing what they should:
- 28. Benefits … Copyright 2014 Does any process have queue open for reading or writing? Has a high water mark been reached? How many messages have been added and removed in a measured interval? Message Persistence == Assured Delivery Queues in stable storage retain messages even if applications fail. Even memory-only queues persist if at least the Queue Manager stays up. Transaction Support - Queue operations are just like reads and writes in a database transaction! Can we combine queue operations AND database operations atomically? (YES!)