title: Potential pitfalls in using a JMS queue?
body: <p>I've been asked to design and implement a system for receiving a high volume of automated sensor data from a large number of devices. This data will be produced at regular intervals and sent to the server as xml in an http post. The devices will keep resending the same data if they don't receive a specific acknowledgment from the server. Some potentially heavy duty processing of this data will need to occur before it's inserted to a number of tables in the main database via a transaction, and additionally some data points will need to be enqueued to be re-directed to other external urls.</p>
  
  <p>I'm planning on using a Java application server (leaning towards GlassFish) with a servlet to receive the incoming data. I'd like to implement some kind of queuing mechanism to store the data temporarily so that the response back to the sensor isn't dependent on all the intermediate processing. Separate independent queues are also a requirement for the data re-direction piece. After doing some research the two main options seem to be:</p>
  
  <p>1) Install a database on the app server and use tables for the various queues. The queues would be processed by a Java application, either running in the app server or standalone as it's own service.</p>
  
  <p>2) Use a database backed JMS solution to implement the queuing.</p>
  
  <p>I'm not that familiar with JMS but from what I've read it seems to be the better solution in this case. The primary requirement is that no sensor data ever be lost or dropped from the queue before being processed and that it be processed more or less sequentially. We'd also like to make it easy to halt the processing of some of the queues at certain times but still have them accumulate data and for these messages to never automatically expire.</p>
  
  <p>With strategy 1 it's obvious to me how to meet these requirements but it may be less robust and scalable, and more complex to develop than strategy 2, since I'll need to write my own multi-threaded code to handle the various independent queues. I'm wondering what the potential pitfalls could be in using JMS queues for this purpose since I've never worked with them before. </p>
  
  <p>Data integrity is a big issue so I need to make sure JMS can guarantee no data loss in the event of a server reboot, power outage, or if the queue gets very large for some reason. For instance could a problem completing transactions to the main database for a period of time potentially cause the JVM to run out of memory, crash, and lose all accumulated data? (This would be the nightmare scenario). </p>
  
  <p>Also, I was wondering if there would be any way to pause the JMS queue processing via an app server admin tool or to easily see what's in the queue (I would be enqueuing an object which would be the message xml plus some other data, including timestamp received, etc.) I've read a few posts on here that deal with related issues but wanted to get some direct feedback. Basically I'd like to know of instances (if any) where JMS is not an appropriate queuing solution and if this is one of those cases. Any advice is greatly appreciated.</p>