What does IMS Queue Control Facility do?
In nonshared-queues environments, IMS Queue Control Facility can query, browse, load, unload, and reprocess messages, provide overflow protection, and rebuild queues after cold starts or emergency restarts of IMS. In shared-queues environments, IMS Queue Control Facility can query, browse, load, unload, and reprocess messages. IMS Sysplex Manager provides more functionality for shared-queues environments.
Product features
IMS Queue Control Facility provides the following capabilities:
| Function | Nonshared-queues environment | Shared-queues environment |
|---|---|---|
| Protects your IMS nonshared-queues system from a queues-full condition (U758 abend) with Queue Space Usage Notification (QSUN). Several features are used to diagnose this condition. | Supported | - |
| Requeues unprocessed messages from your IMS nonshared-queues system onto the IMS message queues after an IMS cold start. | Supported | - |
| Reinserts previously processed messages from your IMS shared- or nonshared-queues system onto the message queues for reprocessing in IMS environments. | Supported | Supported |
| Schedules functions that you specify during an IMS cold start or warm start of your IMS shared- or nonshared-queues system. | Supported | Supported |
| Initiates an offload of the message queues in your IMS nonshared-queues system when a threshold is crossed from A-to-B, B-to-C, C-to-D, and when the threshold that you specify is crossed. | Supported | - |
| Notifies you of specified queue space usage in your IMS nonshared-queues system. | Supported | - |
Performs the following test functions in your IMS
shared- or nonshared-queues system when you need transaction data to simulate production loads or
application input:
|
Supported | Supported |
| Recovers messages from your IMS shared-queues system onto the cold queue after an IMS cold start. | - | Supported |
Queue overflow protection
IMS Queue Control Facility implements queue overflow protection by monitoring the message queue usage. IMS Queue Control Facility analyzes the message queue usage to determine when to send an alert or to take action to prevent the excessive queue usage from continuing.
You can configure queue overflow protection by specifying various parameters to specify partition values, set queue usage limits, and specify appropriate alerts and actions.
IMS Queue Control Facility provides three methods for implementing queue overflow protection. Each subsequent method provides more capability and flexibility in configuring queue overflow protection.
- Type 1
- Queue space notification exit (DFSQSPC0), which is available in your IMS nonshared-queues system
- Type 2
- Queue overflow protection using threshold settings to define queue space partitions in your IMS nonshared-queues system
- Type 3
- Queue overflow protection using area and fail-safe settings to define queue space partitions in your IMS nonshared-queues system
Message processing
You can use IMS Queue Control Facility to process messages from any of the following locations:
- IMS system log
- IMS queue manager message queues
- Shared queues (in a shared-queues environment only)
You can process selected messages based on the criteria that you specify in control statements. IMS Queue Control Facility produces an output data set and a data report that includes quantitative information about the selected messages.
IMS Queue Control Facility supports all types of messages except for Fast Path messages.
Partial support exists for conversational messages. IMS Queue Control Facility requeues conversational messages; however, the conversation is not restarted. Partial support allows the conversational transaction to proceed for an additional iteration.
Recovery and maintenance functions
IMS Queue Control Facility functions are designed to help you perform the following recovery and maintenance tasks:
- Message queue recovery after either a planned or unplanned system outage
- Application recovery when it is practical to return messages to the message queue for reprocessing
- IMS maintenance for shared- and nonshared-queues
environments
You can query, browse, unload, and load IMS messages from, or to, the IMS message queues.
- Load messages to a new IMS release
(for migration) or to an old IMS release
(for fallback)
Messages can be loaded to other IMS systems for testing, offloading, or for recovery purposes.
- Queue overflow protection for nonshared queues
Queue overflow protection monitors queue usage, detects the source of queue overflow, and takes action to prevent your queue usage from reaching critical thresholds.
Message requeuing
- When a system redefinition or failure requires a cold start and messages are lost from the IMS message queue without being processed
- When messages are incorrectly processed because of an application program error
In both of these cases, messages must be returned to the IMS message queue if the messages are to be processed or reprocessed correctly.
- In the nonshared-queues environment, IMS Queue Control Facility gets messages that need to be requeued from the system log data sets (SLDS) or the IMS queue manager message queues.
- In the shared-queues environment, IMS Queue Control Facility gets messages from the cold queue; a special queue for messages that were in process when IMS terminated abnormally and was cold started. Recovery in the shared-queues environment only applies to messages on the cold queue.
You can use IMS Queue Control Facility to maintain the message queues to prevent performance degradation, to save space in the shared queues, and to prevent a buffer shortage.
Queue maintenance
Maintenance of your message queues involves examining the queues and removing only those messages that are no longer needed.
In the shared-queues environment, messages that were in process stay on the cold queue and accumulate until you remove them. This accumulation of messages degrades performance and wastes space on the shared queues.
In the nonshared-queues environment, messages can use enough buffer resource to cause a buffer shortage. A buffer shortage can cause IMS to abnormally terminate with a user 758 abend code.
TSO client / ISPF interface
You can use the IMS Queue Control Facility TSO client (ISPF interface) to perform the following tasks:
- Select the server and IMS subsystem to be used
- Show the IMS environment that you are using
- Show your local queue status
- Query messages and list destinations with queued messages
- Unload (delete) messages from the IMS message queue
- Load or reload messages onto the IMS message queues
- Maintain the tables that are associated with queue overflow protection
You can use the IMS Queue Control Facility TSO client to perform the following queue overflow protection tasks:
- List and perform operations on nonshared-queues environment waited tasks
- View, modify, and load table overflow parameters
- Modify queue space utilization notification parameters