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      <h1>Omnidex Concepts</h1>
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      <p><a href="Partitioning.htm">Partitioning</a></p>
      <p><a href="#limits"><img src="../../images/blank.gif" width="15" height="10" border="0">Limitations</a></p>
      <p><a href="#updates"><img src="../../images/blank.gif" width="15" height="10" border="0">Data Updates</a></p>
      <p><a href="Analysis.htm">1. Analysis</a></p>
      <p><a href="Partition%20the%20Table.htm">2. Partition the Table</a></p>
      <p> <a href="Environment%20File.htm">3. Environment File Entry</a></p>
      <p><a href="Indexing.htm">4. Indexing</a></p>
      <p><a href="Example1.htm">Examples</a></p>
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      <h2 class="line">Partitioning</h2>
      <p>Partitioning is a common RDBMS strategy that turns a large set of data 
        into smaller, logical subsets. The most common objectives for partitioning 
        databases are to make an application perform better and to make the data 
        easier to administrate.</p>
      <p>Omnidex supports partitioning in three ways:</p>
      <ul>
        <li>physical partitioning of data into two or more separate partitions 
        </li>
        <li>partitioning of indexes using composite MDK indexes </li>
        <li>partitioning of indexes using composite ASK indexes </li>
      </ul>
      <p>All three partitioning concepts can be used together or separately and 
        are discussed in detail in this section.</p>
      <h4>What if my data is already partitioned? <a href="#already"><img src="../../images/arrow.gif" width="10" height="10" border="0"><img src="../../images/arrow.gif" width="10" height="10" border="0"></a></h4>
      <p class="line">&nbsp;</p>
      <h3>Advantages</h3>
      <p>Partitioned data can return extraordinary performance on extremely large 
        databases. A partitioned table is broken up into smaller pieces, making 
        the individual table sizes smaller. For example, a table contaning 10 
        billion rows partitioned into 10 partitions, creates 10 one billion row 
        tables. Searching one billion rows is considerably faster than searching 
        10 billion rows, and even faster when installed with Omnidex indexes.</p>
      <p>Physical index files are smaller, narrowing the number of index key values 
        Omnidex must look through to qualify data.</p>
      <p>Index build time can be shorter. For example, a partition can be made 
        up of updates for a given period of time. The new partition can be appended 
        to the end of the existing partitions. The indexes for this new partition 
        can be built without the need to rebuild the indexes on the other partitions.</p>
      <h3>Disadvantages</h3>
      <p> Advance analysis is required to determine the best partitioning strategy, 
        and indeed if the data should be partitioned at all.</p>
      <p>Continual analysis may be required to determine if the current partitioning 
        strategy continues to be the best strategy.</p>
      <p>Since the data is physically separated into different tables, updates 
        to the data must be made to the respective partition. At this time, Omnidex 
        does not handle this automatically.</p>
      <p class="line">&nbsp;</p>
      <h3><a name="limits"></a>Limitations</h3>
      <ul>
        <li>Only child tables can be partitioned.</li>
        <li>Only one partitioned child table per query is allowed.</li>
        <li>Select items containing multiple aggregations in a single expression 
          are not supported.</li>
        <li>Left outer joins TO a partitioned table are not allowed. However, 
          left outer joins FROM a partitioned table are allowed.</li>
        <li>Updates to partitioned data must be made to the individual partition. 
          Omnidex does not handle this automatically. See <a href="#updates">Updating 
          Partitioned Tables</a> (below) for more information.</li>
        <li>MDK Composite keys are limited to 240 bytes.</li>
        <li>Aggregation indexes are limited to 32 values in an IN clause.</li>
        <li>Since each partition will have its own set of indexes and the number 
          of index files is limited to 255 physical files, the number of partitions 
          can be limited.</li>
      </ul>
      <p class="line">&nbsp;</p>
      <h3><a name="updates"></a>Updating Partitioned Tables</h3>
      <p>Applications that update partitioned tables must take some extra steps 
        to make sure the updates are made to the correct partition. Unlike select 
        statements, insert, update and delete statements must reference the individual 
        partition, not the unioned table.</p>
      <p>For example, if the prospects table is partitioned into 5 partitions, 
        where the first partition contains only prospects from the state of California, 
        the second partition contains only prospects from the states of New York 
        and New Jersery, and so one, the application would have to determine which 
        partition to perform the update against according to the state.</p>
      <p>If a prospect from the state of California is inserted into the second 
        partition, which contains only prospects from New York and New Jersey, 
        the new record would never be qualified by any select statement.</p>
      <p>Therefore, the update application must determine which partition should 
        be updated.</p>
      <p class="line">&nbsp;</p>
      <h3><a name="already"></a>What if my data is already partitioned?</h3>
      <p>If the data is already partitioned, analysis is still the first and most 
        important step.</p>
      <ul>
        <li>Is there a <a href="Analysis.htm#pq">partition qualifier</a>?</li>
        <li> Does the partition structure meet the needs of all of my queries?</li>
        <li>Are the partitions relatively close in size (number of rows)?</li>
      </ul>
      <p>The <a href="Analysis.htm">Analysis</a> topic will help to answer the 
        questions and help you determine how to proceed.</p>
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