76 lines
4.8 KiB
HTML
76 lines
4.8 KiB
HTML
<?xml version="1.0" encoding="UTF-8"?>
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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="Query Dispatcher" />
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<meta name="abstract" content="The function of the Dispatcher is to route the query request to either CQE or SQE, depending on the attributes of the query. All queries are processed by the Dispatcher and you cannot bypass it." />
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<meta name="description" content="The function of the Dispatcher is to route the query request to either CQE or SQE, depending on the attributes of the query. All queries are processed by the Dispatcher and you cannot bypass it." />
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<meta name="DC.subject" content="query dispatcher, definitions, query dispatcher" />
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<link rel="stylesheet" type="text/css" href="./ibmdita.css" />
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<title>Query Dispatcher</title>
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</head>
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<body id="rzajqdispatcher"><a name="rzajqdispatcher"><!-- --></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">Query Dispatcher</h1>
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<div><p>The function of the Dispatcher is to route the query request to
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either CQE or SQE, depending on the attributes of the query. All queries are
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processed by the Dispatcher and you cannot bypass it.</p>
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<p><img src="./delta.gif" alt="Start of change" />Currently, the Dispatcher will route an SQL statement to CQE
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if it find that the statement references or contains any of the following: <img src="./deltaend.gif" alt="End of change" /></p>
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<ul><li>INSERT WITH VALUES statement or the target of an INSERT with subselect
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statement</li>
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<li>NLSS or CCSID translation between columns</li>
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<li>Lateral correlation</li>
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<li>Logical files</li>
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<li>Datalink columns</li>
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<li>Tables with Read Triggers</li>
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<li>User-defined table functions</li>
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<li>Read-only queries with more than 1000 dataspaces or updateable queries
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with more than 256 dataspaces.</li>
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<li>DB2<sup>®</sup> Multisystem
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tables</li>
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<li>non-SQL queries, for example the QQQQry API, Query/400, or OPNQRYF</li>
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</ul>
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<p>The Dispatcher also has the built-in capability to re-route an SQL query
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to CQE that was initially routed to SQE. Unless the IGNORE_DERIVED_INDEX
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option with a parameter value of *YES is specified, a query will typically
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be reverted back to CQE from SQE whenever the Optimizer processes table objects
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that have any of the following logical files or indexes defined: </p>
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<ul><li>Logical files with the SELECT/OMIT DDS keyword specified</li>
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<li>Non-standard indexes or derived keys, for example logical files specifying
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the DDS keywords RENAME or Alternate Collating Sequence (ACS) on any field
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referenced in the key</li>
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<li>Sort Sequence NLSS specified for the index or logical file</li>
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</ul>
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<p>As new functionality is added in the future, the Dispatcher will route
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more queries to SQE and increasingly fewer to CQE.</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="queryoptimize.htm" title="DB2 UDB for iSeries provides two query engines to process queries: the Classic Query Engine (CQE) and the SQL Query Engine (SQE).">Query Engine Overview</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="rzajqmqtsupport.htm" title="Although a MQT can contain almost any query, the optimizer only supports a limited set of query functions when matching MQTs to user specified queries. The user specified query and the MQT query must both be supported by the SQE optimizer.">MQT supported function</a></div>
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</div>
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</div>
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</body>
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</html> |