79 lines
7.4 KiB
HTML
79 lines
7.4 KiB
HTML
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<meta name="DC.Type" content="concept" />
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<meta name="DC.Title" content="Journal cache" />
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<meta name="abstract" content="Journal caching is separately chargeable feature with which you can specify that the system cache journal entries in main storage, before writing them to disk. Journal caching is option 42 of the i5/OS operating system." />
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<title>Journal cache</title>
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<h1 class="topictitle1">Journal cache</h1>
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<div><p>Journal caching is separately chargeable feature with which you can specify that the system cache journal entries in main storage, before writing them to disk. Journal caching is option 42 of
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the i5/OS<sup>®</sup> operating system.</p>
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<p>After you have you purchased journal caching, you can specify it with the JRNCACHE parameter on the Create Journal (CRTJRN) or Change Journal (CHGJRN) commands.</p>
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<p>Journal caching provides significant performance improvement for batch applications which perform large numbers of changes to the data portion of the journaled objects. The actions that show a performance
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improvement if journal caching is enabled are as follows:</p>
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<ul><li>Changes to database files from add, update, or delete operations</li>
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<li>Changes to data areas from uses of the change data area command or API</li>
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<li>Changes to data queues from uses of the send data queue API or the receive data queue API</li>
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<li>Changes to integrated file system objects from various write and fclear operations on journaled stream files</li>
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</ul>
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<p>Applications using commitment control will see less improvement (commitment control already performs some journal caching).</p>
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<p>Journal caching modifies the behavior of traditional noncached journaling in batch. Without journal caching, a batch job waits for each new journal entry to be written to disk. Journal caching allows
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most operations to no longer be held up waiting for synchronous disk writes to the journal receiver.</p>
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<p>Journal caching is especially useful for situations where journaling is being used to enable replication to a second system.</p>
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<p>It is not recommended to use journal caching if it is unacceptable to lose even one recent change in the event of a system failure where the contents of main memory are not preserved. This type of journaling
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is directed primarily toward batch jobs and may not be suitable for interactive applications where single system recovery is the primary reason for using journaling.</p>
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<p> Furthermore, the results from the following commands or API will not display the journal entries in the cache:</p>
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<ul><li>Display Journal (DSPJRN) command</li>
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<li>Retrieve Journal Entry (RTVJRNE) command</li>
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<li>Receive Journal Entry (RCVJRNE) command</li>
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<li>Retrieve Journal Entries (QjoRetrieveJournalEntries) API</li>
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</ul>
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<p>The Display Journal Receiver Attributes (DSPJRNRCVA) Command and the Retrieve Journal Receiver Information (QjoRtvJrnReceiverInformation) API show the total number of journal entries in a journal receiver.
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However if some of those entries are in the cache, you cannot see these journal entries using the DSPJRN, RTVJRNE, and RCVJRNE commands, and the QjoRetrieveJournalEntries API. For example, if there are
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100 journal entries in a journal receiver, the DSPJRNRCVA command and QjoRtvJrnReceiverInformation API show that the total number of entries is 100. However, if the last 25 entries are in the journal cache,
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you can only view the first 75 entries.</p>
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<p>Journal caching also affects remote journaling. Journal entries are not sent to the remote system until they are written from the cache to disk. Since journal entries are not sent to the target system
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right away, the number of journal entries that are not confirmed are always greater than if you are not using journal caching.</p>
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<p>Contact your service representative for more information about ordering journal caching.</p>
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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="rzakiplnjrnsu.htm" title="The following topics provide information to plan configuration for journals. They provide information about each option that you can select for journal.">Plan setup for journals</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="rzakijrnsysperform.htm" title="Journal management prevents transactions from being lost if your system ends abnormally or has to be recovered. To do this, journal management writes changes to journaled objects immediately to the journal receiver in auxiliary storage. This increases the disk activity on your system and can have a noticeable affect on system performance. Journaling also increases the overhead associated with opening objects and closing objects.">Journal management and system performance</a></div>
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<div><a href="rzakiguivsgs.htm" title="There are two environments that you can use for journal management: iSeries Navigator and the character-based interface. iSeries Navigator provides a graphical interface for journaling that is easy to use and does not require the use of control language (CL) commands. The character-based interface requires the use of CL commands or APIs, but has more functionality than iSeries Navigator.">iSeries Navigator versus the character-based interface for journaling objects</a></div>
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</div>
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<div class="relref"><strong>Related reference</strong><br />
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<div><a href="../cl/crtjrn.htm">Create Journal (CRTJRN) command</a></div>
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<div><a href="../cl/chgjrn.htm">Change Journal (CHGJRN) command</a></div>
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</div>
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</div>
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