OpenMQ Message Size
Yesterday I was putting in some new hardware for an app that I have that's been running nicely for a while. Unfortunately, the machine is old, getting underpowered for the task at hand, and it was time to update the hardware. At the same time, I wanted to update the message queue system that it was using. About once a month (or so) the existing message broker (Sun ONE Message Queue 3.0.1) will get into a confused and I'll have to restart it. This is bad as it's in a place in the infrastructure where it means that I'll have to restart several things because of the loss of the connection to the message broker.
Now that Sun has open-sourced the message broker, calling it OpenMQ, I decided to update to it and see if it was any better. I got the latest OpenMQ binaries (ver. 4.1) and then unpacked them using jar. There were precious little in the way of instructions, and in the previous version I had used (3.0.1) no configuration was needed. But that would prove to be a mistake for me.
The proper was to configure OpenMQ 4.1 given that it's installed into a directory called $INST is to first update the $INST/mq/etc/imqenv.conf file to include the proper value for IMQ_DEFAULT_JAVAHOME to the location of JDK 1.5.0. For me this was simply:
IMQ_DEFAULT_JAVAHOME=/usr/local/jdk1.5.0
then I wanted to have the default memory size set to at least 4GB, so in $INST/mq/bin/imqbroker look to the line around line 82 that looks like:
_def_jvm_args="-Xms32m -Xmx128m -Xss128k"
and change it to what you want. In my case, I changed it to:
_def_jvm_args="-Xms32m -Xmx4096m -Xss128k"
since I was running a 64-bit JDK 1.5.0 this was going to work out nicely.
The next thing I needed to do (but didn't do at the time) was to set the maximum individual message size to unlimited. The default is 70MB, but there are some messages in my system that are very large. The place to do this is in $INST/mq/lib/props/broker/default.properties on the line that starts with:
imq.message.max_size=70m
and change it to what you want it to be. A value of -1 means unlimited, so I set:
imq.message.max_size=-1
next, for those topics (queues) that are auto-created, there are a few parameters in the section on 'destination based topics' that you might want to use:
imq.autocreate.destination.maxTotalMsgBytes=-1
imq.autocreate.destination.maxNumProducers=500
imq.autocreate.destination.maxBytesPerMsg=-1
the first and last are basically saying "make no limits on the size of an individual message, or the total size of all messages". The middle one is saying that you might want to have a queue that has a lot of producers (injectors) and one consumer (reader), and the default is 100 and it's OK for most folks, but I wanted to make sure that we didn't run into problems if we had clients directly hitting the broker. Now we should be all done with the configuration.
There is an /etc/init.d/imq script in the $INST/mq/etc/init.d directory, but I didn't use that one as I already had one that was working from the 3.0.1 version. All I needed to do was to change the installation location of OpenMQ (the $INST directory) and then it was ready to go. It was already using JDK 1.5.0 and on this machine that means 64-bit.
Add it to the chkconfig start-up on levels 3, 4, and 5 and then start it with /etc/init.d/imq start and all should be just fine.
But that's not how it really happened for me. Here's the problems I ran into to come up with what should have been done in the first place.
First, if you miss the definition of the IMQ_DEFAULT_JAVAHOME variable it means that you have to edit the imqbrokerd script. This was not unusual as I was already in there for the maximum size, so I added that in there and didn't think a thing of it.
Next, if you don't remember to set the maximum message size, then changing it in the default.properties file is not going to be good enough. You have to remove all the data for the instance as I'm convinced that the configuration of the queues is stored in that persistence and the default.properties file is only read when there's nothing in the instance to base the queues off of. So, if you start it without the maximum message length what you need it to be, then you're going to have to shut down IMQ, then remove the entire directory $INST/mq/var/instances/imqbroker. If you don't remove the imqbroker directory I don't think the changes are going to properly work. Thankfully, all my code makes the queues automatically so wiping out the existing configuration is no big deal.
Also for auto-creating queues, you have to remember the two critical size configuration parameters or else you're going to have those queues in trouble when they try to send through large messages. Sure, the 100 producer limit on auto-created topics is reasonable for most installations, but I had talked to another developer here using OpenMQ 4.0 and he had to set it to 500, so I figured that while I was in the config file, I'd up that limit too.
Also, it's important that your app uses the $INST/mq/lib/imq.jar and $INST/mq/lib/jms.jar or else you can have connection problems. Specifically, if going from a 3.x imq.jar to a 4.x IMQ, you're going to get connection errors if you're not using the 4.x imq.jar. So just be safe, get the one with the OpenMQ distribution you're using.