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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en"> <head> <meta http-equiv="Content-Type" content="text/html; charset=us-ascii" /> <meta http-equiv="Content-Style-Type" content="text/css" /> <meta http-equiv="Content-Script-Type" content="text/javascript" /> <title>About Change Apply</title> <meta name="generator" content="Oracle DARB XHTML Converter (Mode = ohj/ohw) - Version 5.1.1 Build 005" /> <meta name="date" content="2009-06-04T17:1:1Z" /> <meta name="robots" content="noarchive" /> <meta name="doctitle" content="About Change Apply" /> <meta name="relnum" content="11g Release 2 (11.2)" /> <meta name="partnum" content="E10703-01" /> <link rel="copyright" href="./dcommon/html/cpyr.htm" title="Copyright" type="text/html" /> <link rel="stylesheet" href="./dcommon/css/blafdoc.css" title="Oracle BLAFDoc" type="text/css" /> <link rel="contents" href="toc.htm" title="Contents" type="text/html" /> <link rel="prev" href="tdpii_repcont005.htm" title="Previous" type="text/html" /> <link rel="next" href="tdpii_repcont007.htm" title="Next" type="text/html" /> <script src="./callback.js" type="text/javascript"></script> <noscript>Your browser does not support JavaScript. This help page requires JavaScript to render correctly.</noscript> </head> <body> <div class="zz-skip-header"><a href="#BEGIN">Skip Headers</a></div> <table class="simple oac_no_warn" summary="" cellspacing="0" cellpadding="0" width="100%"> <col width="86%" /> <col width="*" /> <tr valign="bottom"> <td align="left"></td> <td align="center"><a href="tdpii_repcont005.htm"><img src="./dcommon/gifs/leftnav.gif" alt="Previous" /><br /> <span class="icon">Previous</span></a> </td> <td align="center"><a href="tdpii_repcont007.htm"><img src="./dcommon/gifs/rightnav.gif" alt="Next" /><br /> <span class="icon">Next</span></a></td> </tr> </table> <p><a id="BABBAJFE" name="BABBAJFE"></a><a id="TDPII071" name="TDPII071"></a></p> <div class="sect2"><!-- infolevel="all" infotype="General" --> <h1>About Change Apply<a id="sthref118" name="sthref118"></a><a id="sthref119" name="sthref119"></a></h1> <a name="BEGIN" id="BEGIN"></a> <p>After database changes have been captured and propagated, they reside in a queue and are ready to be applied to complete the replication process. An <span class="bold">apply process</span> is an optional Oracle Database background process that dequeues logical change records (LCRs) and other types of messages from a specific queue. In a simple Oracle Streams replication environment, an apply process typically applies the changes in the LCRs that it dequeues directly to the database objects in the local database.</p> <p>An apply process is always associated with a single queue, and it dequeues messages from this queue only. A single apply process either can dequeue messages from the buffered queue or from the persistent queue, but not both. Therefore, if an apply process applies changes that were captured by a capture process, then the apply process must be configured to dequeue LCRs from the buffered queue. However, if an apply process applies changes that were captured by a synchronous capture, then the apply process must be configured to dequeue LCRs from the persistent queue.</p> <p><a href="#BABHCJAI">Figure: Apply Process</a> shows how an apply process works.</p> <div class="figure"><a id="BABHCJAI" name="BABHCJAI"></a><a id="TDPII222" name="TDPII222"></a> <p class="titleinfigure">Apply Process</p> <img src="img/tdpii013.gif" alt="Description of this figure follows" title="Description of this figure follows" longdesc="img_text/tdpii013.htm" /><br /> <a id="sthref120" name="sthref120" href="img_text/tdpii013.htm">Description of "Apply Process"</a><br /> <br /></div> <!-- class="figure" --> <p>When an apply process cannot apply an LCR successfully, it moves the LCR, and all of the other LCRs in the transaction, to a special queue called the <span class="bold">error queue</span>. The error queue contains all of the current apply errors for a database. If there are multiple apply processes in a database, then the error queue contains the apply errors for each apply process. You can correct the condition that caused an error and then reexecute the corresponding transaction in the error queue to apply its changes. For example, you might modify a row in a table to correct the condition that caused an error in a transaction and then reexecute the transaction.</p> <p><a id="sthref121" name="sthref121"></a><a id="sthref122" name="sthref122"></a><a id="sthref123" name="sthref123"></a>For an apply process to apply changes to a database object, an <span class="bold">instantiation system change number (SCN)</span> must be set for the database object. An instantiation SCN is the SCN for a database object that specifies that only changes that were committed after the SCN at the source database are applied by an apply process. The instantiation SCN for a table assumes that the table is consistent at the source and destination database at the specified SCN. Typically, the instantiation SCN is set automatically when you configure the Oracle Streams replication environment.</p> <div class="helpinfonote"> <p><span class="bold">Note: </span><a id="sthref124" name="sthref124"></a><a id="sthref125" name="sthref125"></a>An apply process can also pass a message that it dequeues to an <span class="bold">apply handler</span>. An apply handler is either a collection of SQL statements or a user-defined PL/SQL procedure that performs custom processing of the message. Apply handlers are beyond the scope of this guide. See <a href="topicid:STRMS175">Message Processing Options for an Apply Process</a> for more information.</p> </div> <div class="helpinfonotealso"> <h2>Related Topics</h2> <p><a href="tdpii_adcont006.htm#CHDIJJGJ">Managing Apply Processes</a></p> <p><a href="tdpii_adcont021.htm#CHDBJIHG">Monitoring Apply Processes</a></p> </div> </div> <!-- class="sect2" --> <!-- Start Footer --> <div class="footer"> <table class="simple oac_no_warn" summary="" cellspacing="0" cellpadding="0" width="100%"> <col width="86%" /> <col width="*" /> <tr> <td align="left"><span class="copyrightlogo">Copyright © 2007, 2009, Oracle and/or its affiliates. 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