Has anyone worked with MQ from RPG?
The problem is as follows. There are several messages in the queue. All of them are with RFH2 header. Each header contains a set of NameValueData.
I am creating a Message Handle and passing it to MQGET. Then I retrieve Properties using MQINQMP.
Question. When I read several messages in a loop, using the same Message Handle instance for all (without freeing it and re-creating it for each message), will I have memory leaks?
The IBM MQ Message Properties API is designed to be used in the following way.
MQOPEN
MQCRTMH
start-loop
MQGET
MQINQMP
end-loop
MQCLOSE
MQDLTMH
You can see this demonstrated in the IBM supplied 'C' sample amqsbcg0.c. I know your question is for RPG, but the underlying API is meant to work the same for all languages.
Related
I am currently exploring de-duplication strategies within Active MQ. Artemis supports duplicate detection, but I'm not sure about ActiveMQ 5
Is it possible to prevent a message from being placed on a queue if it currently exists on the queue in ActiveMQ 5?
Messages which are no longer on the queue and have been so in the past will be allowed back on the queue.
The underlying capability I am trying to achieve is flow control in which multiple messages of the same value are not placed on the queue as to remove duplicate processing.
Based on the documentation, I have tried using the message property defined _AMQ_DUPL_ID, but I am still experiencing duplication. I suspect this may not be supported in ActiveMQ 5 and am unsure what alternative option is. I'm open to suggestions.
NOTE: The Active MQ instance being used is provided by Amazon MQ.
As you suspect, ActiveMQ 5.x doesn't support automatic duplicate detection. This is only supported in ActiveMQ Artemis. That said, messages are not removed from the broker's duplicate ID cache when the message is consumed from the queue. This is because in most cases a duplicate sent after the message is consumed is still considered a duplicate.
You may be able to implement some kind of duplicate detection in a broker plugin, but I have no idea of Amazon MQ supports adding custom plugins. It's more likely that you'll have to implement duplicate detection in the clients themselves.
Is it possible to keep a history of messages (with message content would be perfect) that have already been retrieved and are no longer on a queue?
In the application I can see when the sender attempts to put the message in the queue and when the receiver attempts to pick the messages up, but I'd like to see when the message really arrived into the queue and when the messages were really received.
Does MQ Explorer have this function? How would I use it?
What you are looking for is a message tracking/auditing software for IBM MQ. You can find a list of what is available here.
It is possible to use an API exit to make copies of messages in a queue or to audit both PUT and GET operations.
It is also possible to put messages to a topic, then create as many administrative subscriptions to destination queues as required. Something can then GET and log messages from one of those destination queues. The problem with this is that MQ changes the message ID between publication and consumption whereas in a queue it remains static.
There is no native MQ function to capture messages. It's possible to use linear logs and later scrape the logs but these do not necessarily capture all messages due to optimization. (A message PUT to a waiting getter outside of syncpoint for example.) However there is at least one commercial product to scrape linear transaction logs to audit message activity.
The philosophy of MQ in general is that it is the delivery mechanism and deals with envelope data to route and deliver but does not deal with payload data. WAS, IIB and other broker/transformation engines are where IBM has put all of the functions that deal with message payloads.
Recently I attended an interview, he asked this question
I am putting messages in Q. Manager, but client unable to get that messages, what is the problem can you explain it?
(All permission are ok, and put and get are enable state).
There are a 101 possible reasons. That is why MQ provides an MQRC back to the application, and further information in the AMQERR01.LOG. Without either of those you cannot even begin to guess. (P.S. I suspect that would have been a suitable reply in an interview!!)
But, since you ask for us to guess, here's a few more different from those Valerie suggested.
Perhaps the client channel max message length is shorter than the messages on the queue.
The codepage between client and queue manager may be such that data cannot be converted.
Client application get buffer isn't big enough
Hasn't specified accept truncated and the message was bigger than the buffer
AMS is in use and he's not the intended recipient (different from permissions)
This is a very broad question, would need to check error code received by client. Could be programming situation where client is getting based on a specific message or correl ID that does not exist. Could be that channel auth is blocking client. Also, it could be that the putting application did not commit the messages so they are not really available for the get.
I am working with someone who is trying to achieve a load-balancing behavior using JMS Queues with IBM Websphere MQ. As such, they have multiple Camel JMS consumers configured to read from the same Queue. Despite that this behavior is undefined according to the JMS spec (last time I looked anyway), they expect a sort of round-robin / load-balancing behavior. And, while the spec leaves this undefined, I'm led to believe that the normal behavior of Websphere MQ is to deliver the message to only one of the consumers, and that it may do some type of load-balancing. See here, for example: When multi MessageConsumer connect to same queue(Websphere MQ),how to load balance message-consumer?
But in this particular case, it appears that both consumers are receiving the same message.
Can anyone who is more of an expert with Websphere MQ shed any light on this? Is there any situation where this behavior is expected? Is there any configuration change that can alleviate this?
I'm leaning towards telling everyone here to use the native Websphere MQ clustering facility and go away from having multiple consumers pointing at the same Queue, but that will be a big change for them, so I'd love to discover a way to make this work.
Not that I'm a fan of relying on anything that's undefined, but if they're willing to rely on IBM specific behavior, I'll leave that up to them.
The only way for them to both receive the same messages are:
There are multiple copies of the message.
The apps are browsing the message without a lock, then circling back to delete it.
The apps are backing out a transaction and making the message available again.
The connection is severed before the app acknowledges the message.
Having multiple apps compete for messages in a queue is a recommended practice. If one app goes down the queue is still served. In a cluster this is crucial because the cluster will continue to direct messages to the un-served queue instance until it fills up.
If it's a Dev system, install SupportPac MA0W and tell it to trace just that one queue and you will be able to see exactly what is happening.
See the JMS spec in section 4.4. The provider must never deliver a second copy of an acknowledged message. Exception is made for session handling in 4.4.13 which I cover in #4 above. That's pretty unambiguous and part of the official spec so not an IBM-specific behavior.
What is the best approach to connect to websphere mq v7.1 and clear all the messages of one or more specified queues using Java and JMS? Do I need to use Websphere MQ specific java API? Thanks.
Like all good questions, "it depends."
The queue can be cleared with a command only if there are no open handles on the queue. In that case sending a PCF command to clear the queue is quite effective, but if there are open handles you get back an error. PCF commands are of course a Java feature and not JMS because they are proprietary to WebSphere MQ.
On the other hand, any program authorized to perform destructive gets off a queue can clear the queue. In this case, just loop over a get until you get the 2033 return code indicating the queue is empty. This can be performed using JMS or Java but both of these manage the input buffer for you. If the queue is REALLY deep then you end up moving all that data and if the app is client connected, you are moving it at network speed instead of in memory.
To get around this, you need to specify a minimal amount of buffer and as one of the GET options also specify MQGMO.TRUNCATED_MSG_ACCEPTED. This moves only the message header during the get calls and can be significantly faster.
Finally, if you are doing this programamtically and regardless of which method you use, spin off several threads and don't use syncpoint. You actually have to go out of your way to get exclusive input on a queue so once you get a session, just spawn many threads off of it. Close each thread gracefully and shut down the the session once all the threads are closed.