How Documentum Print Control Services Works

December 15, 2011 at 1:18 pm | Posted in Architecture | 1 Comment
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This is the second part of a mini series of articles on Documentum Print Control Services (PCS) and how to use it effectively. The first part provided an introduction and overview of PCS. In this article I will take a much more in-depth technical look at the product.

PCS consists of a number of components:

  • A DFS-based web service that is deployed on a JBoss application server
  • A set of DARS that contain services that can be used by user-facing applications
  • Optional WDK components for Webtop and Taskspace (as mentioned in the first article this PCS support is built into Documentum Compliance Manager)

As we will see later PCS also relies on PDF and Postscript rendition generation so DTS or ADTS is required.

So what happens when a controlled print request is issued from an application? The printing user-interface will usually collect some information from the user relating to the object to be printed. This will include the name of the printer and a reason for the print. Once the request is received by the application server control will be passed to the PCS ControlPrintService.requestPrint() function.

The requestPrint function does 3 things. First PDF Stamping Services (PSS) is used to create a watermarked copy of the main PDF rendition. I may cover PSS in more depth in another article, however the key point here is PSS takes an existing PDF rendition and generates a watermarked PDF that can include metadata overlaid in headers, footers or other areas of the document. PCS and PSS have tight integration where PSS exposes a Controlled Print-specific configuration and PCS can pass in Controlled Print attributes such as copy number, recipient and printing reason to be watermarked on the document.

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Next a dmc_pss_print_copy object is created in the repository. The watermarked PDF is the primary rendition for this object and the object is linked to the /Temp/PCSCopies folder. At this point the object’s print_status attribute is set to ‘Created’.

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Finally, a request for a Postscript rendition for the dmc_pss_print_copy object is made. The rendition will have a page_modifier of ‘PS4Print’. The server will wait for up to 2 minutes for the rendition to be generated and then return to the caller. Either way the print_status field is set to ‘PsRequested’. Up to now all the processing is synchronous, but now control is returned to the user of application.

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At this point the user is probably expecting the printer to output the printed document, however no print request has yet been sent to a printer, there is simply a dmc_pcs_print_copy object created possibly waiting for Postscript rendition to be created. There are 2 asynchronous task still required to be completed. First the Postscript rendition needs to be created:

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Of course it may have been created during the earlier synchronous processing but there is no guarantee. Continuous uninterrupted operation of controlled printing requires that your DTS or ADTS infrastructure is resilient, scalable and sized for all the rendition requests generated in a production environment. If your users have requested prints that don’t seem to be appearing your first port of call for troubleshooting is to confirm that DTS/ADTS is working and that Postscript renditions are being created for your dmc_pss_print_copy objects.

The Print Control Services server is ultimately responsible for sending your document to the required printer. Calling the Print Control Services server is the responsibility of the PcsAsyncPrintJob. For controlled print (and recall) requests to be completed in a reasonable amount of time this job needs to be set to run every couple of minutes and needs to be monitored for regular execution and successful job completion.

When PcsAsyncPrintJob runs it queries for all dmc_pss_print_copy objects that have print_status = ‘PsRequested’.

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For each dmc_pss_print_copy object the PCSAsyncPrintJob does the following:

  1. Ensures that a Postscript rendition has been created. If not no further processing is done on this execution of the job.
  2. Then calls the remote ControlPrintService DFS endpoint on the PCS server, calling the ‘print’ method.

Once the print request is received by ControlPrintService component the following happens:

  • The audittrail is checked to ensure that the same document has not been printed with the requested copy number. If for some reason there is already an audittrail entry for this copy number an error is raised.
  • The postscript file is sent to the printer using the Java Printing Service API.
  • The service monitors the print job until completion (or failure) and then returns a response to the PcsAsyncPrintJob job.
  • Creates an audittrail entry to record the controlled print

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The actual “printing” part of PCS is carried out using the Java Printing Services (JPS) API. If you are going to be making use of PCS in your organisation it may be worth your while getting to know the JPS a little better. I’ll discuss JPS in more depth in a later article. Once PCS has sent the document for printing it sets the print_status attribute to ‘PrintRequested’ – this is the last status update for the document. Note you only know that PCS has requested a print from the printer – there is no way for PCS to ‘know’ whether that print was successful and so it can not update the object further.

The key points to take away from this article are as follows:

  1. First, when the WDK application server returns control back to the user after a print request has been made there is no guarantee that the document has been sent to the printer. There are 2 layers of asynchronous processing required to print a document; depending on the speed, capacity and availability of the relevant servers it may take some time for the print to appear.
  2. Second the print may even not appear at all if there is a problem with one of the asynchronous components. This fact may not be obvious to the end user who may just assume that printing is “slow”.

1 Comment »

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  1. This is a very interesting post. The Documentum environment introduces some challenging performance issues. Detecting the specific components causing problems in an architecture which features customized Webtop front ends, load balancers, C++ based content servers, reporting servers and databases is not easy. I’d be interested to see if there are tools and strategies to address these concerns.

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