123 lines
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HTML
123 lines
9.6 KiB
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<meta name="abstract" content="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." />
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<title>Journal management and system performance</title>
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</head>
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<body id="rzakijrnsysperform"><a name="rzakijrnsysperform"><!-- --></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">Journal management and system performance</h1>
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<div><p>Journal management prevents transactions from being lost if your
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system ends abnormally or has to be recovered. To do this, journal management
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writes changes to journaled objects immediately to the journal receiver in
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auxiliary storage. This increases the disk activity on your system and can
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have a noticeable affect on system performance. Journaling also increases
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the overhead associated with opening objects and closing objects.</p>
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<p>As the number of objects you are journaling increases, the general performance
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of the system can be slower. The time it takes to perform an IPL on your system
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can also increase, particularly if your system ends abnormally.</p>
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<p>The system takes measures to minimize the performance effect of using journaling
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features. For example, the system packages before-images and after-images
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and any access path changes for a record in a single write operation to auxiliary
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storage. Therefore, journaling access paths and before-images, in addition
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to after-images, usually does not cause additional performance overhead. However,
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they do add to the auxiliary storage requirements for journaling.</p>
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<p> The system also spreads journal receivers across multiple disk units to
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improve performance. If you do not specify a maximum receiver-size option,
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then the system can place the journal receiver on up to ten disk units in
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a disk pool. If you specify a maximum receiver-size option, then the system
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can place the journal receiver on up to 100 disk units in a disk pool. </p>
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<p>You can take measures to minimize the effect of journaling on your system
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performance:</p>
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<ul><li>Consider using journal caching. Journal caching is a separately chargeable
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feature that causes the system to write journal entries to memory in large
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groups. When there are several journal entries in memory then the system writes
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journal entries from memory to disk. If the application performs a large number
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of changes, this can result in fewer synchronous disk writes resulting in
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improved performance. However, when you use journal caching, you sacrifice
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single system recovery because the entries that are still in the cache might
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be lost on an abnormal IPL.</li>
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<li>Do not set the force-write ratio (FRCRATIO) parameter for physical files
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that you are journaling. You can let the system manage when to write records
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for the physical file to disk because the journal receiver has a force-write
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ratio of 1.</li>
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<li>Isolate journal receivers in a disk pool that is not the system disk pool,
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if the separate disk pool has at least two disk arms. This reduces contention
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when accessing the disks. If the separate disk pool does not have at least
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two disk arms, there is no performance benefit. For optimal performance, ensure
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that your I/O processors have adequate write cache. Performance can be better
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if the disk units in the disk pool are protected through device parity protection
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rather than mirrored.</li>
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<li>Consider using record blocking when a program processes a journaled file
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sequentially (SEQONLY(*YES)). When you add or insert records to the file,
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the records are not written to the journal receiver until the block is filled.
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You can specify record blocking with the Override with Database File (OVRDBF)
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command or in some high-level language programs. If you use the OVRDBF command,
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do the following: <ul><li>Set the SEQONLY parameter to (*YES).</li>
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<li>Use a large enough value for the NBRRCDS parameter to make the buffer
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approach the optimal size of 128KB.</li>
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</ul>
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</li>
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<li>Consider minimizing the fixed-length portion of the journal entry using
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RCVSIZOPT(*MINFIXLEN) for the journal. When you specify this option, all of
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the data that is selectable by the FIXLENDTA parameter is not deposited. Therefore,
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that information does not have to be retrieved, benefiting journal performance.</li>
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<li>Consider omitting information from the journal entry you do not need using
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the OMTJRNE parameter. When you specify the OMTJRNE parameter for database
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physical files you will not deposit the file open and close entries which
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saves processing as well as disk storage space. Similarly, if you specify
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the OMTJRNE parameter for directories and stream files, the object open, close,
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and force entries are not deposited.</li>
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<li>Ensure you have enough write cache for your I/O processor (IOP).</li>
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</ul>
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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="rzakiconcepts.htm" title="This topic explains how journal management works, why to use it, and how it affects your system.">Journal management concepts</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="rzakisizeoptions.htm" title="A journal receiver holds journal entries that you might use for recovery and entries that the system might use for recovery. For example, you might use record level entries, such as database record changes, and file level entries, such as the entry for opening or closing a file. Also, the system writes entries that you never see or use, such as entries for explicitly journaled access paths, for SMAPP, or for commitment control.">Receiver size options for journals</a></div>
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<div><a href="rzakijrncache.htm" title="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.">Journal cache</a></div>
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<div><a href="rzakidiskarm.htm" title="Journaling affects the disk arms that store the journal receiver.">Frequently asked questions about journaling and disk arm usage</a></div>
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<div><a href="../rzahx/rzahx1.htm">Performance</a></div>
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<div><a href="../rzaly/rzalydmkickoff.htm">Disk management</a></div>
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<div><a href="http://www.redbooks.ibm.com/abstracts/sg246286.html?Open" target="_blank">Striving for Optimal Journal Performance on DB2 Universal Database for iSeries</a></div>
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</div>
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<div class="reltasks"><strong>Related tasks</strong><br />
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<div><a href="rzakiperform.htm" title="There are two main performance objectives for the remote journal function. To provide a timely delivery of journal entries to a target system and to minimize impacts to the journaling throughput on the source system.">Factors that affect remote journal performance</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/ovrdbf.htm">Override with Database File (OVRDBF) command</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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