Databases
StackOverflow2013
Postsdbo
POConcurrent processing of messages with strict order
 

Note that there are some explanatory texts on larger screens.

plurals
  1. POConcurrent processing of messages with strict order
    primarykey
    data
    text
    <p>Within my JavaEE web application, I need to process incoming messages strictly in the order of arrival. I assume that my webapp container (Tomcat 6) retains the order of messages as they arrive at the http port.</p> <p>What causes headaches to me, is the way I am internally processing these messages. For improved workload, I append the processing of each message to a ThreadPool as many things need to be done here e.g. XML parsing, sometimes enrichment of data using external web services. After processing is finished, I push the java representation of the message into a complex stream processing engine <a href="http://esper.codehaus.org" rel="nofollow noreferrer">esper.codehaus.org</a>, which is threadsafe. Here, different patterns are checked where the entrance order is the highest requirement e.g threshold of a phenomenon exceeds.</p> <p>I had the idea of inserting every processed message into a PriorityQueue with a priority ID they received at time of arrival (in my Servlet, where it is incremented for each message). The problem is the following:</p> <p>The thread which is polling the elements from the queue (lowest ID is the head of the queue) for inserting it into esper could skip an ID as it does not check for missing items. I guess an illustration works out better:</p> <p><img src="https://i.stack.imgur.com/6stff.png" alt="enter image description here"></p> <p>For steps (1) to (4) everything works as intended. But at step (5) the QueuePoller retrieves element 6 and not element 4 (which is later inserted at step (6)). This results in the message order: 2; 3; 6; 4.</p> <p>What I tried to do was to alter the implementation of polling the queue's head to follow the strict order of IDs. Meaning, if the next ID's element is not yet inserted into the queue, wait at a barrier until its there. This seemed to work for the first 10 minutes but then hanged, probably due to an element that never got inserted into the queue.</p> <p>Anyone out there having a similar problem in the past and has some hint for me? </p>
    singulars
    1. PO
      singulars
      1. PTAnswer
    1. This table or related slice is empty.
    1. PTQuestion
    1. USskaffman
    1. USmatthes
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. PO
      singulars
      1. PTAnswer
    2. PO
      singulars
      1. PTAnswer
    3. PO
      singulars
      1. PTAnswer
    1. VO
      singulars
      1. POConcurrent processing of messages with strict order
      1. This table or related slice is empty.
      1. VTUpMod
    2. VO
      singulars
      1. POConcurrent processing of messages with strict order
      1. USxea
      1. VTFavorite
    3. VO
      singulars
      1. POConcurrent processing of messages with strict order
      1. This table or related slice is empty.
      1. VTUpMod
    1. COYou might be better creating the queue items as soon as they arrive at your server then only allow them to be taken from the queue in order and once processing of them is complete.
      singulars
      1. POConcurrent processing of messages with strict order
      1. USNick Wilson
    2. COWhat I don't understand is, if the order of elements in the output queue has to match the order in the input queue, what good is processing them out-of-order? That is, why do 6 before 4 if QueuePoller needs to have 4 before 6?
      singulars
      1. POConcurrent processing of messages with strict order
      1. USaib
    3. COi thought about that two, but I guess it would lead to similar results. Assuming, I would use a flag which indicates that processing is finished, same problems could arise if something went wrong in the processing (server timeout, etc. which is imho also the problem why the element is not inserted). Thus, the indicator flag would never be set to true.
      singulars
      1. POConcurrent processing of messages with strict order
      1. USmatthes
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload