What do change events look like?

I was using my Python programs for processing MQ PCF data, and was testing them out with different sorts of MQ data. I found the documentation for change events in the IBM knowledge centre is a bit sparse, so here is some information on it.

I did

• define QL(DELETEME)
• alter ql(DELETEME) descr(‘change comment’)
• delete QL(DELETEME)

For define and delete there is one event message created. For alter there are two messages created, one contains before data the other has the after data.

The MD looks like

"MQMD":{
     "StrucId":"MD  ",
     "Version":1,
     "Report":"NONE",
     "MsgType":"DATAGRAM",
     "Expiry":-1,
     "Feedback":"NONE",
     "Encoding":546,
     "CodedCharSetId":1208,
     "Format":"MQEVENT ",
     "Priority":0,
     "Persistence":"NOT_PERSISTENT",
     "MsgId":"0x414d5120514d4120202020202020202020…",
     "CorrelId":"0x414d5120514d4120202020202020202020…",
     "BackoutCount":0,
     "ReplyToQ":"  ",
     "ReplyToQMgr":"QMA",
     "UserIdentifier":"            ",
     "AccountingToken":"0x0000…",
     "ApplIdentityData":"  ",
     "PutApplType":"QMGR",
     "PutApplName":"QMA   ",
     "PutDate":"20190217",
     "PutTime":"11141373",
     "ApplOriginData":"    ",
     "GroupId":"0x000000...",
     "MsgSeqNumber":1,
     "Offset":0,
     "MsgFlags":0,
     "OriginalLength":-1
   },

When a change event occurs the MD for the “after” message is effectively the same but note the MsgID is different, and the CorrelId is the same, so you will need to clear the MsgId and keep the CorrelID when getting the second message.

For the create command the PCF header was

"Header":{
     "Type":"EVENT",
     "StrucLength":36,
     "Version":2,
     "Command":"CONFIG_EVENT",
     "MsgSeqNumber":1,
     "Control":"LAST",
     "CompCode":0,
     "Reason":2367,  "CONFIG_CREATE_OBJECT"
     "ParameterCount":58,
     },

For the delete command the PCF header was

"Header":{
     "Type":"EVENT",
     "StrucLength":36,
     "Version":2,
     "Command":"CONFIG_EVENT",
     "MsgSeqNumber":1,
     "Control":"LAST",
     "CompCode":0,
     "Reason":2369, "CONFIG_DELETE_OBJECT
     "ParameterCount":58

}

For the alter/change command the PCF headers were

"Header":{
     "Type":"EVENT",
     "StrucLength":36,
     "Version":2,
     "Command":"CONFIG_EVENT",
     "MsgSeqNumber":1,
     "Control":"NOT_LAST",
     "CompCode":0,
     "Reason":2368,
     "ParameterCount":58    
   },

and

"Header":{
     "Type":"EVENT",
     "StrucLength":36,
     "Version":2,
     "Command":"CONFIG_EVENT",
     "MsgSeqNumber":2,
     "Control":"LAST",
     "CompCode":0,
     "Reason":2368, "CONFIG_CHANGE_OBJECT"
     "ParameterCount":58
   },

The differences are the MsgSeqNumber value and Control being NOT_LAST or LAST.

The data is common to all requests. You need to compare the fields in both the records for the change event, to see which are different. With the data in Python dict – this was a trivial exercise.

"Data":{

    "EVENT_USER_ID":"colinpaice",

    "EVENT_ORIGIN":"CONSOLE",

    "EVENT_Q_MGR":"QMA",

    "OBJECT_TYPE":"Q",

    "Q_NAME":"DELETEME",

    "Q_DESC":"",

    …

    "Q_TYPE":"LOCAL"

  }

after the change

"Data":{
     "EVENT_USER_ID":"colinpaice",
     "EVENT_ORIGIN":"CONSOLE",
     "EVENT_Q_MGR":"QMA",
     "OBJECT_TYPE":"Q",
     "Q_NAME":"DELETEME",
     "Q_DESC":"change comment",
     …
     "ALTERATION_DATE":"2019-02-17",
     "ALTERATION_TIME":"11.14.33",
     …
     "Q_TYPE":"LOCAL"
   }

When I printed out the changed data, the first time ALTERATION_DATA and ALTERATION_TIME were both displayed. The second time, only ALTERATION_TIME was displayed. I thought this was a bug in my program. After checking my program, it was obvious… If I change the queue 10 minutes later – the ALTERATION_DATE does not change – so remember to report both of these, and not just the change values.