85 lines
5.9 KiB
HTML
85 lines
5.9 KiB
HTML
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<title>Other distributed relational database terms and concepts</title>
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<body id="rbal1odbconc"><a name="rbal1odbconc"><!-- --></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">Other distributed relational database terms and concepts</h1>
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<div><p>This discussion provides an overview of additional distributed
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relational database concepts.</p>
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<p>On IBM<sup>®</sup> systems, some distributed relational database support
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is provided by the DB2 Universal Database™ for Linux<sup>®</sup>, UNIX<sup>®</sup> and Windows<sup>®</sup> and DataPropagator™ for iSeries™ products.
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In addition, you can use some of these concepts when writing <span class="keyword">iSeries</span> application
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programs.</p>
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<p>DB2
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Universal Database™ for <span class="keyword">iSeries</span> supports
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both the remote unit of work and distributed unit of work with Advanced Program-to-Program
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Communications (APPC) and TCP/IP communications, starting in OS/400<sup>®</sup> V5R1.
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A degree of processing sophistication beyond the distributed unit of work
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is a <dfn class="term">distributed request</dfn>. This type of distributed relational
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database access enables a user or application program to issue a single SQL
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statement that can read or update data at multiple locations.</p>
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<p>Tables in a distributed relational database do not have to differ from
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one another. Some tables can be exact or partial copies of one another. Extracts,
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snapshots, and replication are terms that describe types of copies using distributed
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processing.</p>
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<p><dfn class="term">Extracts</dfn> are user-requested copies of tables. The copies are
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extracted from one database and loaded into another specified by the user.
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The unloading and loading process might be repeated periodically to obtain
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updated data. Extracts are most useful for one-time or infrequent occurrences,
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such as read-only copies of data that rarely changes.</p>
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<p><dfn class="term">Snapshots</dfn> are read-only copies of tables that are automatically
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made by a server. The server refreshes these copies from the source table
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on a periodic basis specified by the user—perhaps daily, weekly, or monthly.
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Snapshots are most useful for locations that seek an automatic process for
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receiving updated information on a periodic basis.</p>
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<p>Data <dfn class="term">replication</dfn> means the server automatically updates copies
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of a table. It is similar to snapshots because copies of a table are stored
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at multiple locations. Data replication is most effective for situations that
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require high reliability and quick data retrieval with few updates.</p>
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<p>Tables can also be split across computer servers in the network. Such a
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table is called a <dfn class="term">distributed table</dfn>. Distributed tables are split
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either horizontally by rows or vertically by columns to provide easier local
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reference and storage. The columns of a vertically distributed table reside
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at various locations, as do the rows of a horizontally distributed table.
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At any location, the user still sees the table as if it were kept in a single
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location. Distributing tables is most effective when the request to access
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and update certain portions of the table come from the same location as those
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portions of the table.</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="rbal1drdbp.htm" title="A relational database is a set of data stored in one or more tables in a computer.">Distributed relational database processing</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="rbal1drdh.htm" title="DB2 Universal Database for i5/OS provides all the database management functions for i5/OS. Distributed relational database support on the system is an integral part of the operating system, just as is support for communications, work management, security functions and other functions.">Distributed relational database on i5/OS</a></div>
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</div>
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