128 lines
8.4 KiB
HTML
128 lines
8.4 KiB
HTML
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<!DOCTYPE html
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PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<meta name="DC.Type" content="concept" />
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<meta name="DC.Title" content="Wait for more records when end of file is reached" />
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<meta name="abstract" content="End-of-file delay is a method of continuing to read sequentially from a database file (logical or physical) after an end-of-file condition occurs." />
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<meta name="description" content="End-of-file delay is a method of continuing to read sequentially from a database file (logical or physical) after an end-of-file condition occurs." />
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<meta name="DC.subject" content="end-of-file, waiting for more records" />
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<meta name="keywords" content="end-of-file, waiting for more records" />
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<meta name="DC.Relation" scheme="URI" content="../rzaks/rzaks1.htm" />
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<meta name="copyright" content="(C) Copyright IBM Corporation 1998, 2006" />
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<title>Wait for more records when end of file is reached</title>
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</head>
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<body id="rbafoefdel"><a name="rbafoefdel"><!-- --></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">Wait for more records when end of file is reached</h1>
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<div><p>End-of-file delay is a method of continuing to read sequentially
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from a database file (logical or physical) after an end-of-file condition
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occurs.</p>
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<p>When an end-of-file condition occurs on a file being read sequentially
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(for example, next/previous record) and you have specified an end-of-file
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delay time (EOFDLY parameter on the Override with Database File (OVRDBF) command),
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the system waits for the time you specified.</p>
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<p>At the end of the delay time, another read is done to determine if any
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new records were added to the file. If records were added, normal record processing
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is done until an end-of-file condition occurs again. If records were not added
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to the file, the system waits again for the time specified. Special consideration
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should be taken when using end-of-file delay on a logical file with select/omit
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specifications, opened so that the keyed sequence access path is not used.
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In this case, after end-of-file is reached, the system retrieves only those
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records added to a based-on physical file that meet the select/omit specifications
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of the logical file.</p>
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<p>Also, special consideration should be taken when using end-of-file delay
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on a file with a keyed sequence access path, opened so that the keyed sequence
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access path is used. In this case, after end-of-file is reached, the system
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retrieves only those records added to the file or those records updated in
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the file that meet the specification of the read operation using the keyed
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sequence access path.</p>
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<p>For example, end-of-file delay is used on a keyed file that has a numeric
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key field in ascending order. An application program reads the records in
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the file using the keyed sequence access path. The application program performs
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a read next operation and gets a record that has a key value of 99. The application
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program performs another read next and no more records are found in the file,
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so the system attempts to read the file again after the specified end-of-file
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delay time. If a record is added to the file or a record is updated, and the
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record has a key value less than 99, the system does not retrieve the record.
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If a record is added to the file or a record is updated and the record has
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a key value greater than or equal to 99, the system retrieves the record.</p>
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<p>For end-of-file delay times equal to or greater than 10 seconds, the job
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is eligible to be removed from main storage during the wait time. If you do
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not want the job eligible to be moved from main storage, specify PURGE(*NO)
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on the Create Class (CRTCLS) command for the CLASS the job is using.</p>
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<p>To
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indicate which jobs have an end-of-file delay in progress, the status field
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of the Work with Active Jobs (WRKACTJOB) display shows an end-of-file wait
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or end-of-file activity level for jobs that are waiting for a record.</p>
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<p>If a job uses end-of-file-delay and commitment control, it can hold its
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record locks for a longer period of time. This increases the chances that
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some other job can try to access those same records and be locked out. For
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that reason, be careful when using end-of-file-delay and commitment control
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in the same job.</p>
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<p>If a file is shared, the OVRDBF command specifying an end-of-file delay
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must be requested before the <em>first</em> open of the file because overrides
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are ignored that are specified after the shared file is opened.</p>
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<div class="p">There are several ways to end a job that is waiting for more records because
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of an end-of-file-delay specified on the OVRDBF command: <ul><li>Write a record to the file with the end-of-file-delay that will be recognized
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by the application program as a last record. The application program can then
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specify a force-end-of-data (FEOD) operation. An FEOD operation allows the
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program to complete normal end-of-file processing.</li>
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<li>Do a controlled end of a job by specifying OPTION(*CNTRLD) on the End
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Job (ENDJOB) command, with a DELAY parameter value time greater than the EOFDLY
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time. The DELAY parameter time specified must allow time for the EOFDLY time
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to run out, time to process any new records that have been put in the file,
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and any end-of-file processing required in your application. After new records
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are processed, the system signals end of file, and a normal end-of-file condition
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occurs.</li>
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<li>Specify OPTION(*IMMED) on the ENDJOB command. No end-of-file processing
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is done.</li>
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<li>If the job is interactive, press the System Request key to end the last
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request.</li>
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</ul>
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</div>
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<p>The following example shows an end-of-file delay operation:</p>
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<br /><img src="rbafo541.gif" alt="Example of end-of-file delay operation" /><br /><p>The actual processing of the EOFDLY parameter is more complex than shown
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because it is possible to force a true end-of-file if OPTION(*CNTRLD) on the
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ENDJOB command is used with a long delay time.</p>
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<div class="p">The job does not become active whenever a new record is added to the file.
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The job becomes active after the specified end-of-file delay time ends. When
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the job becomes active, the system checks for any new records. If new records
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were added, the application program gets control and processes all new records,
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then waits again. Because of this, the job takes on the characteristic of
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a batch job when it is processing. For example, it normally processes a batch
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of requests. When the batch is completed, the job becomes inactive. If the
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delay is small, you can cause excessive system overhead because of the internal
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processing required to start the job and check for new records. Normally,
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only a small amount of overhead is used for a job waiting during end-of-file
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delay. <div class="note"><span class="notetitle">Note:</span> When the job is inactive (waiting) it is in a long-wait status,
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which means it was released from an activity level. After the long-wait status
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is satisfied, the system reschedules the job in an activity level.</div>
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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="rbaforddbf.htm" title="The iSeries system provides a number of ways to read database records.">Read database records</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="../rzaks/rzaks1.htm">Work management</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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