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| author | Lorry <lorry@roadtrain.codethink.co.uk> | 2012-07-20 20:00:05 +0100 |
|---|---|---|
| committer | Lorry <lorry@roadtrain.codethink.co.uk> | 2012-07-20 20:00:05 +0100 |
| commit | 3ef782d3745ea8f25a3151561a3cfb882190210e (patch) | |
| tree | 86b9c2f5fde051dd0bced99b3fc9f5a3ba08db69 /docs/programmer_reference/cam_fail.html | |
| download | berkeleydb-3ef782d3745ea8f25a3151561a3cfb882190210e.tar.gz | |
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| -rw-r--r-- | docs/programmer_reference/cam_fail.html | 127 |
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diff --git a/docs/programmer_reference/cam_fail.html b/docs/programmer_reference/cam_fail.html new file mode 100644 index 00000000..f638350d --- /dev/null +++ b/docs/programmer_reference/cam_fail.html @@ -0,0 +1,127 @@ +<?xml version="1.0" encoding="UTF-8" standalone="no"?> +<!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"> + <head> + <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /> + <title>Handling failure in Data Store and Concurrent Data Store applications</title> + <link rel="stylesheet" href="gettingStarted.css" type="text/css" /> + <meta name="generator" content="DocBook XSL Stylesheets V1.73.2" /> + <link rel="start" href="index.html" title="Berkeley DB Programmer's Reference Guide" /> + <link rel="up" href="cam.html" title="Chapter 10. Berkeley DB Concurrent Data Store Applications" /> + <link rel="prev" href="cam.html" title="Chapter 10. Berkeley DB Concurrent Data Store Applications" /> + <link rel="next" href="cam_app.html" title="Architecting Data Store and Concurrent Data Store applications" /> + </head> + <body> + <div xmlns="" class="navheader"> + <div class="libver"> + <p>Library Version 11.2.5.3</p> + </div> + <table width="100%" summary="Navigation header"> + <tr> + <th colspan="3" align="center">Handling failure in Data Store and Concurrent Data Store applications</th> + </tr> + <tr> + <td width="20%" align="left"><a accesskey="p" href="cam.html">Prev</a> </td> + <th width="60%" align="center">Chapter 10. + Berkeley DB Concurrent Data Store Applications + </th> + <td width="20%" align="right"> <a accesskey="n" href="cam_app.html">Next</a></td> + </tr> + </table> + <hr /> + </div> + <div class="sect1" lang="en" xml:lang="en"> + <div class="titlepage"> + <div> + <div> + <h2 class="title" style="clear: both"><a id="cam_fail"></a>Handling failure in Data Store and Concurrent Data Store applications</h2> + </div> + </div> + </div> + <p>When building Data Store and Concurrent Data Store applications, there +are design issues to consider whenever a thread of control with open +Berkeley DB handles fails for any reason (where a thread of control may be +either a true thread or a process).</p> + <p>The simplest case is handling system failure for any Data Store or +Concurrent Data Store application. In the case of system failure, it +doesn't matter if the application has opened a database environment or +is just using standalone databases: if the system fails, after the +application has modified a database and has not subsequently flushed the +database to stable storage (by calling either the <a href="../api_reference/C/dbclose.html" class="olink">DB->close()</a>, +<a href="../api_reference/C/dbsync.html" class="olink">DB->sync()</a> or <a href="../api_reference/C/mempsync.html" class="olink">DB_ENV->memp_sync()</a> methods), the database may be left in a +corrupted state. In this case, before accessing the database again, the +database should either be:</p> + <div class="itemizedlist"> + <ul type="disc"> + <li>removed and re-created,</li> + <li>removed and restored from the last known good backup, or</li> + <li>verified using the <a href="../api_reference/C/dbverify.html" class="olink">DB->verify()</a> method or <a href="../api_reference/C/db_verify.html" class="olink">db_verify</a> utility. If +the database does not verify cleanly, the contents may be salvaged using +the <span class="bold"><strong>-R</strong></span> and <span class="bold"><strong>-r</strong></span> options of the <a href="../api_reference/C/db_dump.html" class="olink">db_dump</a> utility.</li> + </ul> + </div> + <p>Applications where the potential for data loss is unacceptable should +consider the Berkeley DB Transactional Data Store product, which offers standard transactional +durability guarantees, including recoverability after failure.</p> + <p>Additionally, system failure requires that any persistent database +environment (that is, any database environment not created using the +<a href="../api_reference/C/envopen.html#envopen_DB_PRIVATE" class="olink">DB_PRIVATE</a> flag), be removed. Database environments may be +removed using the <a href="../api_reference/C/envremove.html" class="olink">DB_ENV->remove()</a> method. If the persistent database +environment was backed by the filesystem (that is, the environment was +not created using the <a href="../api_reference/C/envopen.html#envopen_DB_SYSTEM_MEM" class="olink">DB_SYSTEM_MEM</a> flag), the database +environment may also be safely removed by deleting the environment's +files with standard system utilities.</p> + <p>The second case is application failure for a Data Store application, +with or without a database environment, or application failure for a +Concurrent Data Store application without a database environment: as in +the case of system failure, if any thread of control fails, after the +application has modified a database and has not subsequently flushed the +database to stable storage, the database may be left in a corrupted +state. In this case, the database should be handled as described +previously in the system failure case.</p> + <p>The third case is application failure for a Concurrent Data Store +application with a database environment. There are resources maintained +in database environments that may be left locked if a thread of control +exits without first closing all open Berkeley DB handles. Concurrent Data +Store applications with database environments have an additional option +for handling the unexpected exit of a thread of control, the +<a href="../api_reference/C/envfailchk.html" class="olink">DB_ENV->failchk()</a> method.</p> + <p>The <a href="../api_reference/C/envfailchk.html" class="olink">DB_ENV->failchk()</a> will return <a class="link" href="program_errorret.html#program_errorret.DB_RUNRECOVERY">DB_RUNRECOVERY</a> if the +database environment is unusable as a result of the thread of control +failure. (If a data structure mutex or a database write lock is left +held by thread of control failure, the application should not continue +to use the database environment, as subsequent use of the environment +is likely to result in threads of control convoying behind the held +locks.) The <a href="../api_reference/C/envfailchk.html" class="olink">DB_ENV->failchk()</a> call will release any database read +locks that have been left held by the exit of a thread of control. In +this case, the application can continue to use the database +environment.</p> + <p>A Concurrent Data Store application recovering from a thread of control +failure should call <a href="../api_reference/C/envfailchk.html" class="olink">DB_ENV->failchk()</a>, and, if it returns success, +the application can continue. If <a href="../api_reference/C/envfailchk.html" class="olink">DB_ENV->failchk()</a> returns +<a class="link" href="program_errorret.html#program_errorret.DB_RUNRECOVERY">DB_RUNRECOVERY</a>, the application should proceed as described for +the case of system failure.</p> + </div> + <div class="navfooter"> + <hr /> + <table width="100%" summary="Navigation footer"> + <tr> + <td width="40%" align="left"><a accesskey="p" href="cam.html">Prev</a> </td> + <td width="20%" align="center"> + <a accesskey="u" href="cam.html">Up</a> + </td> + <td width="40%" align="right"> <a accesskey="n" href="cam_app.html">Next</a></td> + </tr> + <tr> + <td width="40%" align="left" valign="top">Chapter 10. + Berkeley DB Concurrent Data Store Applications + </td> + <td width="20%" align="center"> + <a accesskey="h" href="index.html">Home</a> + </td> + <td width="40%" align="right" valign="top"> Architecting Data Store and Concurrent Data Store applications</td> + </tr> + </table> + </div> + </body> +</html> |