We are using IBM MQ and recently we faced an issue where some messages that were declared as sent to the MQ server by our client application were not consumed by our MQ consumer.
We lacked logging produced/consumed messages so we tried to check messages in MQ server log/data.
We found that messages are stored in /var/mqm/qmgrs/MQ_MANAGER/queues/ but we didn't find there all messages in the queue file (old messages were not found)
What is the rollover policy of IBM MQ and where does old queues files go?
That's not how the queue files work. They are not rollover logs. The same space is continually overwritten as needed to store messages, but messages may not be written there at all if they can be processed through memory caches etc.
PERSISTENT messages are usually logged in files under /var/mqm/log, but there are circumstances where even that can be avoided. Your qmgr's recovery logfile configuration (circular/linear etc) will determine whether historic information about PERSISTENT messages remains available.
NONPERSISTENT messages are never logged in those files.
In IBM MQ messages can be either persistent or non-persistent.
If a message is persistent it will normally be written to the transactional logs (usually under /var/mqm/log/MQ_MANAGER/active) before a commit completes or before the PUT completes if not done under a unit of work.
If a message is non-persistent it will not be written to the transactional logs.
At this point either type of message may reside only in memory and will only be written to the queue file (usually under /var/mqm/qmgrs/MQ_MANAGER/queues) if it needs to offload memory or if it is persistent and a check point is taken.
If the message is consumed in a timely manner it may never be written to the queue file.
The queue file will shrink in size if space taken up by messages that are no longer needed is in use, this happens automatically and is not configurable or documented by IBM as far as I know.
Non-persistent messages generally do not survive a queue manager restart.
Transactional logs can be configured as circular or linear. If circular the logs will be reused once they are no longer needed. If linear with automatic log management (introduced in 9.0.2) they will work similarly to circular. If linear without automatic log management, what happens to logs that are no longer needed would be based on your own log management.
If the message is still in the transactional log you may be able to view it as described in "Where's my message? Tool and instructions to use the MQ recovery log to find out what happened to your persistent MQ messages on distributed platforms".
Related
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.
I am using ActiveMQ where I need following requirements
To have very fast consumers as my producers are already very fast
Need processing at lease 2K messages per second
Not require to process/consume messages again in case of server crash or other failures. I can trigger whole process again.
Needs to run very normal configuration server - 4Gib RAM
I have configured ActiveMQ as given below
Using non-persistent delivery mode (vm://localhost)(http://activemq.apache.org/what-is-the-difference-between-persistent-and-non-persistent-delivery.html)
Using spring integration for put/fetch messages in/from queue/channel.
Using max-concurrent-consumers with 10 threads
Assume all other configs are by default with ActiveMQ and Sprig-integration.
Problems/Questions
I am not sure how ActiveMQ stores messages in case of non-persistent delivery mode, is it possible that my process will fail with out of memory errors once my queue size exceed some limit? I am asking this because it's very difficult to test whole process for me. So I needs to be aware about limitation before I trigger the process.
If non-persistent delivery mode is not sufficient with my above requirements, is there any performance tuning tips with which I can achieve my requirements with persistent delivery mode (tcp://). I have already tested with this mode, but it seems consumers are very slow here. Also, I have already tried to use DUPS_OK_ACKNOWLEDGE to make my consumer fast with persistent delivery mode but no luck.
NOTE : I am using latest ActiveMQ version 5.14
I am not sure how ActiveMQ stores messages in case of non-persistent delivery mode
Activemq store messages in the memory at first, and it will also swap it to the disk(there is a tmp_storage folder in activemq's data path).
is it possible that my process will fail with out of memory errors once my queue size exceed some limit
I have never met out of memory in activemq, even with about one million messages.
You can also make sure by the producer flow control(http://activemq.apache.org/producer-flow-control.html).
You can make the producer hang when there is too many messages not consumed.
And about performance of persistent delivery, I also have no good methods.
We are using IBM MQ8.0. Activitiy logs are getting logged for outgoing messages which we are sending to external system. But there is no log available for the messages which are from external system to our MQ Manager.
Is it problem with client channel configuration ?
Or MQ logging configuration issue ?
IBM describes these "activity logs" as recover logs in the Knowledge center page "Making sure that messages are not lost (logging)"
IBM MQ records all significant changes to the persistent data controlled by the queue manager in a recovery log.
This includes creating and deleting objects, persistent message updates, transaction states, changes to object attributes, and channel activities. The log contains the information you need to recover all updates to message queues by:
Keeping records of queue manager changes
Keeping records of queue updates for use by the restart process
Enabling you to restore data after a hardware or software failure
Please note that non-persistent messages are not logged to the recover log.
Based on your question it is likely that the messages you are sending to the external system are persistent messages and the messages you are receiving from the external system are non-persistent messages, this would explain why they are not logged to the recover log files.
Persistence is determined at the time the message is first PUT.
IBM has a good Technote "Message persistence FAQs" about this subject.
Q3. What is the best way to be certain that messages are persistent?
A3. Set MQMD message persistence to persistent (MQPER_PERSISTENT), or nonpersistent (MQPER_NOT_PERSISTENT) and your message will always retain that value.
Note: MQPER_PERSISTENCE_AS_Q_DEF is the default setting for the persistence value in the MQMD. See the persistence values listed below.
...
Additional information
MQPER_PERSISTENCE_AS_Q_DEF can lead to unexpected results. If there is more than one definition in the queue-name resolution path, the default persistence attribute is taken from first queue definition in the path at the time of the MQPUT or MQPUT1 call. This queue could be an:
alias queue
local queue
local definition of a remote queue
queue-manager alias
transmission queue
cluster queue
The external system will need to make sure the messages they send you are set as persistent messages if you want them to be logged.
I am using circular logging. Because of human intervention, one of the
queue files is corrupted.
Since the circular logging is not having the ability of recovering the
corrupted queue files, what will be the next steps it will take?
Will queue manager create an empty queue file for that queue and start
enrolling the messages to it? Else, it will just show the pending
messages in the queue but not allow the applications to process?
As you correctly note, MQ cannot recover from a damaged queue file when it is configured for circular logging.
Will queue manager create an empty queue file for that queue and start enrolling the messages to it? Else, it will just show the pending messages in the queue but not allow the applications to process?
None of the above. The queue manager will return an error to any process attempting to access that queue.
When a queue file is damaged, it may or may not have had messages in it. There is no automatic recovery possible that would correctly reconcile the state of any messages that may have been enqueued, therefore no further processing is done on that queue and any access returns an error. Human intervention is required in that case and the fix is to delete and redefine the queue using runmqsc.
If additional queue recovery is required to make sure messages are not lost in such cases, linear logging is mandatory.
The queue manager is not going to create an new queue file automatically. If you truly have a corrupted queue then you may have to delete and recreate it. It would be helpful if you can provide more info about the error you see indicating the queue is corrupt. Also, what version of MQ are you using?
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.