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Specifying the maximum number of active channels

 

We can also specify the maximum number of active channels. We can do this to prevent your system being overloaded by a large number of starting channels. If you use this method, you should set the disconnect interval attribute to a low value to allow waiting channels to start as soon as other channels terminate.

Each time a channel that is retrying attempts to establish connection with its partner, it must become an active channel. If the attempt fails, it remains a current channel that is not active, until it is time for the next attempt. The number of times that a channel will retry, and how often, is determined by the retry count and retry interval channel attributes. There are short and long values for both these attributes. See Channel attributes for more information.

When a channel has to become an active channel (because a START command has been issued, or because it has been triggered, or because it is time for another retry attempt), but is unable to do so because the number of active channels is already at the maximum value, the channel waits until one of the active slots is freed by another channel instance ceasing to be active. If, however, a channel is starting because it is being initiated remotely, and there are no active slots available for it at that time, the remote initiation is rejected.

Whenever a channel, other than a requester channel, is attempting to become active, it goes into the STARTING state. This is true even if there is an active slot immediately available, although in this case it will only be in STARTING state for a very short time. However, if the channel has to wait for an active slot, it is in STARTING state while it is waiting.

Requester channels do not go into STARTING state. If a requester channel cannot start because the number of active channels is already at the limit, the channel ends abnormally.

Whenever a channel, other than a requester channel, is unable to get an active slot, and so waits for one, a message is written to the log or the z/OS console, and an event is generated. When a slot is subsequently freed and the channel is able to acquire it, another message and event are generated. Neither of these events and messages are generated if the channel is able to acquire a slot straightaway.

If a STOP CHANNEL command is issued while the channel is waiting to become active, the channel goes to STOPPED state. A Channel-Stopped event is raised as usual.

Server-connection channels are included in the maximum number of active channels.

For more information about specifying the maximum number of active channels, see the WebSphere MQ System Administration Guide for WebSphere MQ for UNIX systems, and Windows systems, the WebSphere MQ for iSeries System Administration Guide for WebSphere MQ for iSeries, or WebSphere MQ Script (MQSC) Command Reference for WebSphere MQ for z/OS.

 

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