The ups and downs of MQ Reconnect – how can I tell if automatic reconnect has happened.

This is one topic in a series of blog posts.

The MQ reconnection support make any reconnection transparent to the application code.

You can specify an MQ Call Back function, MQCB, and specify a routine which gets control asynchronously when events happen. See sample code amqsphac.c described here.

The specified call back function gets control whenever there is an event. You can then take actions such as print out information, for example

  • switch…
  • case MQRC_RECONNECTED:
    • printf(“%sEVENT : Connection Reconnected\n”,TimeStamp);
    • break;

You could extend this to set a flag in global storage, or write an event message to aid problem determination.

Running an application and issuing the endmqm -r QMA command, the exit produced

14:43:25 : EVENT : Connection Reconnecting (Delay: 1055ms)
14:43:26 : EVENT : Connection Reconnected

Which showed it connected to another queue manager after a short interval.

With only one queue manager active, and issuing endmqm -r QMA

the messages were

14:44:32 : EVENT : Connection Reconnecting (Delay: 1021ms)
14:44:34 : EVENT : Connection Reconnecting (Delay: 2122ms)
14:44:36 : EVENT : Connection Reconnecting (Delay: 4572ms)
14:44:40 : EVENT : Connection Reconnecting (Delay: 4819ms)
14:44:45 : EVENT : Connection Reconnecting (Delay: 4609ms)
14:44:50 : EVENT : Connection Reconnecting (Delay: 4262ms)
14:44:54 : EVENT : Connection Reconnecting (Delay: 4151ms)
14:44:58 : EVENT : Connection Reconnecting (Delay: 4035ms)
14:45:02 : EVENT : Connection Reconnecting (Delay: 4616ms)
14:45:02 : EVENT : Reconnection failed
14:45:02 : EVENT : Connection Broken

In the mqclient.ini file I had

CHANNELS:
   ServerConnectionParms=COLIN/TCP/127.0.0.1(1414),127.0.0.1(1416)
   MQReconnectTimeout=30
   ReconDelay=(1000,200)(2000,200)(4000,1000)

The time between first detecting a problem, 14:44:32 and 14:45:02 : EVENT : Reconnection failed, was the time specified in MQReconnectTimeout=30 (seconds).

The reconnections were tried after the times in ReconDelay=(1000,200)(2000,200)(4000,1000).

For (1000,200) this says try connecting after 1000 ms + a random time in interval between 0 and 200 ms. The first interval was 1021 ms.

See here for more information.

 

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