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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>Overview of Active Session History</title> <meta name="generator" content="Oracle DARB XHTML Converter (Mode = ohj/ohw) - Version 5.1.1 Build 005" /> <meta name="date" content="2009-05-27T15:13:2Z" /> <meta name="robots" content="noarchive" /> <meta name="doctitle" content="Overview of Active Session History" /> <meta name="relnum" content="11g Release 2 (11.2)" /> <meta name="partnum" content="E10822-01" /> <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="tdppt_transient.htm" title="Previous" type="text/html" /> <link rel="next" href="tdppt_transient002.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="tdppt_transient.htm"><img src="./dcommon/gifs/leftnav.gif" alt="Previous" /><br /> <span class="icon">Previous</span></a> </td> <td align="center"><a href="tdppt_transient002.htm"><img src="./dcommon/gifs/rightnav.gif" alt="Next" /><br /> <span class="icon">Next</span></a></td> </tr> </table> <p><a id="DAFIJFGE" name="DAFIJFGE"></a><a id="TDPPT065" name="TDPPT065"></a></p> <div class="sect1"><!-- infolevel="all" infotype="General" --> <h1>Overview of Active Session History</h1> <a name="BEGIN" id="BEGIN"></a> <p>To capture a detailed history of database activity, Oracle Database samples active sessions<a id="sthref189" name="sthref189"></a><a id="sthref190" name="sthref190"></a> each second with the Active Session History<a id="sthref191" name="sthref191"></a> (ASH) sampler. AWR snapshot processing collects the sampled data into memory and writes it to persistent storage. ASH is an integral part of the Oracle Database self-management framework and is extremely useful for diagnosing performance problems.</p> <p>ASH gathers sampled data the session level rather than at the instance level. By capturing statistics for only active sessions, ASH represents a manageable set of data. The size of this data is directly related to the work being performed, rather than to the entire database instance.</p> <p>Sampled data captured by ASH can be aggregated based on the various dimensions that it captures, including the following:</p> <ul> <li> <p>SQL identifier of a SQL statement</p> </li> <li> <p>Object number, file number, and block number</p> </li> <li> <p>Wait event identifier and parameters</p> </li> <li> <p>Session identifier and session serial number</p> </li> <li> <p>Module and action name</p> </li> <li> <p>Client identifier of the session</p> </li> <li> <p>Service hash identifier</p> </li> </ul> <p>You can run ASH reports<a id="sthref192" name="sthref192"></a> to analyze transient performance problems with the database that only occur during specific times. This technique is especially useful when you are trying to do either of the following:</p> <ul> <li> <p>Resolve transient performance problems that may last for only a short period of time, such as why a particular job or session is not responding when the rest of the instance is performing as usual</p> </li> <li> <p>Perform scoped or targeted performance analysis by various dimensions or their combinations, such as time, session, module, action, or SQL identifier</p> </li> </ul> <div class="helpinfonotealso"> <h2>Related Topics</h2> <p><a href="tdppt_method005.htm#CIHBEFGH">Active Session History Statistics</a></p> <p><a href="tdppt_transient.htm#CHDHHDHE">Resolving Transient Performance Problems</a></p> </div> </div> <!-- class="sect1" --> <!-- 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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