1<!--$Id: config.so,v 10.22 2008/04/23 14:50:45 margo Exp $--> 2<!--Copyright (c) 1997,2008 Oracle. All rights reserved.--> 3<!--See the file LICENSE for redistribution information.--> 4<html> 5<head> 6<title>Berkeley DB Reference Guide: Configuring locking</title> 7<meta name="description" content="Berkeley DB: An embedded database programmatic toolkit."> 8<meta name="keywords" content="embedded,database,programmatic,toolkit,btree,hash,hashing,transaction,transactions,locking,logging,access method,access methods,Java,C,C++"> 9</head> 10<body bgcolor=white> 11<a name="2"><!--meow--></a> 12<table width="100%"><tr valign=top> 13<td><b><dl><dt>Berkeley DB Reference Guide:<dd>Locking Subsystem</dl></b></td> 14<td align=right><a href="../lock/intro.html"><img src="../../images/prev.gif" alt="Prev"></a><a href="../toc.html"><img src="../../images/ref.gif" alt="Ref"></a><a href="../lock/max.html"><img src="../../images/next.gif" alt="Next"></a> 15</td></tr></table> 16<p align=center><b>Configuring locking</b></p> 17<p>The <a href="../../api_c/env_set_lk_detect.html">DB_ENV->set_lk_detect</a> method specifies that the deadlock detector 18should be run whenever a lock is about to block. This option provides 19for rapid detection of deadlocks at the expense of potentially frequent 20invocations of the deadlock detector. On a fast processor with a highly 21contentious application where response time is critical, this is a good 22choice. An option argument to the <a href="../../api_c/env_set_lk_detect.html">DB_ENV->set_lk_detect</a> method 23indicates which lock requests should be rejected.</p> 24<p>The application can limit how long it blocks on a contested resource. 25The <a href="../../api_c/env_set_timeout.html">DB_ENV->set_timeout</a> method specifies the length of the timeout. 26This value is checked whenever deadlock detection is performed, 27so the accuracy of the timeout depends upon the frequency of 28deadlock detection.</p> 29<p>In general, when applications are not specifying lock and transaction 30timeout values, the <a href="../../api_c/env_set_lk_detect.html#DB_LOCK_DEFAULT">DB_LOCK_DEFAULT</a> option is probably the 31correct first choice, and other options should only be selected based 32on evidence that they improve transaction throughput. If an application 33has long-running transactions, <a href="../../api_c/env_set_lk_detect.html#DB_LOCK_YOUNGEST">DB_LOCK_YOUNGEST</a> will guarantee 34that transactions eventually complete, but it may do so at the expense 35of a large number of lock request rejections (and therefore, transaction 36aborts).</p> 37<p>The alternative to using the <a href="../../api_c/env_set_lk_detect.html">DB_ENV->set_lk_detect</a> method is to 38explicitly perform deadlock detection using the Berkeley DB 39<a href="../../api_c/lock_detect.html">DB_ENV->lock_detect</a> method.</p> 40<p>The <a href="../../api_c/env_set_lk_conflicts.html">DB_ENV->set_lk_conflicts</a> method allows you to specify your own 41locking conflicts matrix. This is an advanced configuration option, 42and is almost never necessary.</p> 43<table width="100%"><tr><td><br></td><td align=right><a href="../lock/intro.html"><img src="../../images/prev.gif" alt="Prev"></a><a href="../toc.html"><img src="../../images/ref.gif" alt="Ref"></a><a href="../lock/max.html"><img src="../../images/next.gif" alt="Next"></a> 44</td></tr></table> 45<p><font size=1>Copyright (c) 1996,2008 Oracle. All rights reserved.</font> 46</body> 47</html> 48
