95 lines
6.1 KiB
HTML
95 lines
6.1 KiB
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<meta name="DC.Title" content="Determining whether to use data queues or user queues" />
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<meta name="abstract" content="If user queues and data queues supply the same function, which one should you choose for your implementation? The following is a comparison of the two and an insight into when you should use one queue rather than the other." />
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<title>Determining whether to use data queues or user queues</title>
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<body id="exdqdetermine"><a name="exdqdetermine"><!-- --></a>
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<!-- Java sync-link --><script language="Javascript" src="../rzahg/synch.js" type="text/javascript"></script>
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<h1 class="topictitle1">Determining whether to use data queues or user queues</h1>
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<div><p>If user queues and data queues supply the same function, which
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one should you choose for your implementation? The following is a comparison
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of the two and an insight into when you should use one queue rather than the
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other.</p>
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<div class="section"><p>First, your programming experience is an important
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consideration in selecting a queue type. If you are familiar with C or MI
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programming, you may want to select the user queue. User queues can be accessed
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only using MI, and MI can be used only by ILE RPG, ILE COBOL, C, and MI programs.</p>
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<p>Next,
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performance plays an important part in determining what type of queue to use.
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As stated in System APIs or CL commands--when to use each, APIs generally
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give better performance than CL commands. Also, MI instructions perform better
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than an external call to an API because APIs have overhead associated with
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them. User queues use MI instructions to manipulate entries; data queues use
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APIs. Therefore, the user queue has better performance than the data queue.</p>
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<p>Last,
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you need to consider how the queue entries are manipulated. For example, you
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need a way to perform enqueue and dequeue operations on entries from a queue.
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As stated earlier, user queues use MI instructions to manipulate entries.
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Specifically, you use the ENQ MI instruction to enqueue a message, and the
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DEQ MI instruction to dequeue a message. If you are running at security level
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40 or greater, you must ensure that the user queue is created in the user
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domain in order to directly manipulate a user queue using MI instructions.
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Because data queue entries are manipulated by APIs, the security level of
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the machine does not limit the use of the API.</p>
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<p>You cannot create a user
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queue object in a library that does not permit user-domain objects, which
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is determined by the QALWUSRDMN system value. (See Domain concepts for more
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information on QALWUSRDMN.) Data queues are always created in the system domain,
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so there is no problem with the data queue being created into a specific library.</p>
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<p>The
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following is a summary to help you select the type of queue that is right
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for your program:</p>
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<ul><li>Use user queues when: <ul><li>You have a programming background in MI.</li>
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<li>You need the additional performance of an API for creating and deleting
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and MI instructions for manipulating entries.</li>
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<li>You do not need to create a user-domain queue into a library where the
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QALWUSRDMN system value does not permit user-domain user objects when at security
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level 40 or 50.</li>
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</ul>
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</li>
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<li>Use data queues when: <ul><li>You have a programming background in or prefer to program in a high-level
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language such as COBOL, C, or RPG.</li>
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<li>You do not need the additional performance of MI instructions for directly
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manipulating entries.</li>
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<li>You need to create queues into a library that is not listed in the QALWUSRDMN
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system value.</li>
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</ul>
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</li>
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</ul>
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</div>
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</div>
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<div>
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<div class="familylinks">
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<div class="parentlink"><strong>Parent topic:</strong> <a href="ExTaskDataque.htm" title="Data queues and user queues both provide a means for one or more processes to communicate asynchronously. The queues can be processed FIFO (first-in first-out), LIFO (last-in first-out), or by key.">Examples: Using data queues or user queues</a></div>
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</div>
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<div class="relconcepts"><strong>Related concepts</strong><br />
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<div><a href="conDomain.htm" title="All objects are assigned a domain attribute when they are created.">Domain concepts</a></div>
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<div><a href="aboutapis.htm" title="Describes most of the iSeries application programming interfaces (APIs), as well as some APIs for related products that can be used on iSeries servers.">About application programming interfaces (APIs)</a></div>
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</div>
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</div>
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</body>
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</html>
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