mirror of
https://github.com/berkeleydb/libdb.git
synced 2024-11-16 17:16:25 +00:00
336 lines
13 KiB
HTML
336 lines
13 KiB
HTML
<?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>Recovery Procedures</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="Getting Started with Berkeley DB Transaction Processing" />
|
||
<link rel="up" href="filemanagement.html" title="Chapter 5. Managing DB Files" />
|
||
<link rel="prev" href="backuprestore.html" title="Backup Procedures" />
|
||
<link rel="next" href="architectrecovery.html" title="Designing Your Application for Recovery" />
|
||
</head>
|
||
<body>
|
||
<div xmlns="" class="navheader">
|
||
<div class="libver">
|
||
<p>Library Version 11.2.5.2</p>
|
||
</div>
|
||
<table width="100%" summary="Navigation header">
|
||
<tr>
|
||
<th colspan="3" align="center">Recovery Procedures</th>
|
||
</tr>
|
||
<tr>
|
||
<td width="20%" align="left"><a accesskey="p" href="backuprestore.html">Prev</a> </td>
|
||
<th width="60%" align="center">Chapter 5. Managing DB Files</th>
|
||
<td width="20%" align="right"> <a accesskey="n" href="architectrecovery.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="recovery"></a>Recovery Procedures</h2>
|
||
</div>
|
||
</div>
|
||
</div>
|
||
<div class="toc">
|
||
<dl>
|
||
<dt>
|
||
<span class="sect2">
|
||
<a href="recovery.html#normalrecovery">Normal Recovery</a>
|
||
</span>
|
||
</dt>
|
||
<dt>
|
||
<span class="sect2">
|
||
<a href="recovery.html#catastrophicrecovery">Catastrophic Recovery</a>
|
||
</span>
|
||
</dt>
|
||
</dl>
|
||
</div>
|
||
<p>
|
||
DB supports two types of recovery:
|
||
</p>
|
||
<div class="itemizedlist">
|
||
<ul type="disc">
|
||
<li>
|
||
<p>
|
||
Normal recovery, which is run when your environment is
|
||
opened upon application startup, examines only those
|
||
log records needed to bring the databases to a consistent
|
||
state since the last checkpoint. Normal recovery
|
||
starts with any logs used by any transactions active at
|
||
the time of the last checkpoint, and examines all logs
|
||
from then to the current logs.
|
||
</p>
|
||
</li>
|
||
<li>
|
||
<p>
|
||
Catastrophic recovery, which is performed in the same
|
||
way that normal recovery is except that it examines
|
||
all available log files. You use catastrophic recovery
|
||
to restore your databases from a previously created backup.
|
||
</p>
|
||
</li>
|
||
</ul>
|
||
</div>
|
||
<p>
|
||
Of these two, normal recovery should be considered a routine
|
||
matter; in fact you should run normal
|
||
recovery whenever you start up your application.
|
||
</p>
|
||
<p>
|
||
Catastrophic recovery is run whenever you have lost or
|
||
corrupted your database files and you want to restore from a
|
||
backup. You also run catastrophic recovery when
|
||
you create a hot backup
|
||
(see <a class="xref" href="hotfailover.html" title="Using Hot Failovers">Using Hot Failovers</a> for more information).
|
||
</p>
|
||
<div class="sect2" lang="en" xml:lang="en">
|
||
<div class="titlepage">
|
||
<div>
|
||
<div>
|
||
<h3 class="title"><a id="normalrecovery"></a>Normal Recovery</h3>
|
||
</div>
|
||
</div>
|
||
</div>
|
||
<p>
|
||
Normal recovery examines the contents of your environment's
|
||
log files, and uses this information to ensure that your
|
||
database files are consistent relative to the
|
||
information contained in the log files.
|
||
</p>
|
||
<p>
|
||
Normal recovery also recreates your environment's region files.
|
||
This has the desired effect of clearing any unreleased locks
|
||
that your application may have held at the time of an
|
||
unclean application shutdown.
|
||
</p>
|
||
<p>
|
||
Normal recovery is run only against those log files created
|
||
since the time of your last checkpoint. For this reason,
|
||
your recovery time is dependent on how much data has been
|
||
written since the last checkpoint, and therefore on how
|
||
much log file information there is to examine. If you run
|
||
checkpoints infrequently, then normal recovery can
|
||
take a relatively long time.
|
||
</p>
|
||
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
|
||
<h3 class="title">Note</h3>
|
||
<p>
|
||
You should run normal recovery every
|
||
time you perform application startup.
|
||
</p>
|
||
</div>
|
||
<p>
|
||
To run normal recovery:
|
||
</p>
|
||
<div class="itemizedlist">
|
||
<ul type="disc">
|
||
<li>
|
||
<p>
|
||
Make sure all your environment handles are closed.
|
||
</p>
|
||
</li>
|
||
<li>
|
||
<p>
|
||
Normal recovery <span class="emphasis"><em>must
|
||
be</em></span> single-threaded.
|
||
</p>
|
||
</li>
|
||
<li>
|
||
<p>
|
||
Provide the <code class="literal">DB_RECOVER</code> flag when
|
||
you open your environment.
|
||
</p>
|
||
</li>
|
||
</ul>
|
||
</div>
|
||
<p>
|
||
You can also run recovery by pausing or shutting down your
|
||
application and using the <span class="command"><strong>db_recover</strong></span>
|
||
command line utility.
|
||
</p>
|
||
<p>
|
||
For example:
|
||
</p>
|
||
<pre class="programlisting">#include <stdio.h>
|
||
#include <stdlib.h>
|
||
#include "db.h"
|
||
|
||
int
|
||
main(void)
|
||
{
|
||
int ret;
|
||
u_int32_t env_flags;
|
||
DB_ENV *envp;
|
||
const char *db_home_dir = "/tmp/myEnvironment";
|
||
|
||
envp = NULL;
|
||
|
||
/* Open the environment */
|
||
ret = db_env_create(&envp, 0);
|
||
if (ret != 0) {
|
||
fprintf(stderr, "Error creating environment handle: %s\n",
|
||
db_strerror(ret));
|
||
return (EXIT_FAILURE);
|
||
}
|
||
|
||
/* Open the environment, specifying that recovery is to be run. */
|
||
env_flags = DB_CREATE | /* If the environment does not
|
||
* exist, create it. */
|
||
DB_INIT_LOCK | /* Initialize locking */
|
||
DB_INIT_LOG | /* Initialize logging */
|
||
DB_INIT_MPOOL | /* Initialize the cache */
|
||
DB_THREAD | /* Free-thread the env handle. */
|
||
DB_INIT_TXN | /* Initialize transactions */
|
||
DB_RECOVER; /* Run normal recovery */
|
||
|
||
/* Open the environment. */
|
||
ret = envp->open(envp, db_home_dir, env_flags, 0);
|
||
if (ret != 0) {
|
||
fprintf(stderr, "Error opening environment: %s\n",
|
||
db_strerror(ret));
|
||
goto err;
|
||
}
|
||
|
||
...
|
||
/*
|
||
* All other operations are identical from here. Notice, however,
|
||
* that we have not created any other threads of control before
|
||
* recovery is complete. You want to run recovery for
|
||
* the first thread in your application that opens an environment,
|
||
* but not for any subsequent threads.
|
||
*/ </pre>
|
||
</div>
|
||
<div class="sect2" lang="en" xml:lang="en">
|
||
<div class="titlepage">
|
||
<div>
|
||
<div>
|
||
<h3 class="title"><a id="catastrophicrecovery"></a>Catastrophic Recovery</h3>
|
||
</div>
|
||
</div>
|
||
</div>
|
||
<p>
|
||
Use catastrophic recovery when you are
|
||
recovering your databases from a previously created backup.
|
||
Note that to restore your databases from a previous backup, you
|
||
should copy the backup to a new environment directory, and
|
||
then run catastrophic recovery. Failure to do so can lead to
|
||
the internal database structures being out of sync with your log files.
|
||
</p>
|
||
<p>
|
||
Catastrophic recovery must be run single-threaded.
|
||
</p>
|
||
<p>
|
||
To run catastrophic recovery:
|
||
</p>
|
||
<div class="itemizedlist">
|
||
<ul type="disc">
|
||
<li>
|
||
<p>
|
||
Shutdown all database operations.
|
||
</p>
|
||
</li>
|
||
<li>
|
||
<p>
|
||
Restore the backup to an empty directory.
|
||
</p>
|
||
</li>
|
||
<li>
|
||
<p>
|
||
Provide the <code class="literal">DB_RECOVER_FATAL</code> flag when
|
||
you open your environment. This environment open
|
||
must be single-threaded.
|
||
</p>
|
||
</li>
|
||
</ul>
|
||
</div>
|
||
<p>
|
||
You can also run recovery by pausing or shutting down your
|
||
application and using the <span class="command"><strong>db_recover</strong></span>
|
||
command line utility with the the <code class="literal">-c</code> option.
|
||
</p>
|
||
<p>
|
||
Note that catastrophic recovery examines every available
|
||
log file — not just those log files created since the
|
||
last checkpoint as is the case for normal recovery. For this reason,
|
||
catastrophic recovery is likely to take longer than does
|
||
normal recovery.
|
||
</p>
|
||
<p>
|
||
For example:
|
||
</p>
|
||
<pre class="programlisting">#include <stdio.h>
|
||
#include <stdlib.h>
|
||
#include "db.h"
|
||
|
||
int
|
||
main(void)
|
||
{
|
||
int ret;
|
||
u_int32_t env_flags;
|
||
DB_ENV *envp;
|
||
const char *db_home_dir = "/tmp/myEnvironment";
|
||
|
||
envp = NULL;
|
||
|
||
/* Open the environment */
|
||
ret = db_env_create(&envp, 0);
|
||
if (ret != 0) {
|
||
fprintf(stderr, "Error creating environment handle: %s\n",
|
||
db_strerror(ret));
|
||
return (EXIT_FAILURE);
|
||
}
|
||
|
||
/* Open the environment, specifying that recovery is to be run. */
|
||
env_flags = DB_CREATE | /* If the environment does not
|
||
* exist, create it. */
|
||
DB_INIT_LOCK | /* Initialize locking */
|
||
DB_INIT_LOG | /* Initialize logging */
|
||
DB_INIT_MPOOL | /* Initialize the cache */
|
||
DB_THREAD | /* Free-thread the env handle. */
|
||
DB_INIT_TXN | /* Initialize transactions */
|
||
<strong class="userinput"><code>DB_RECOVER_FATAL; /* Run catastrophic recovery */</code></strong>
|
||
|
||
/* Open the environment. */
|
||
ret = envp->open(envp, db_home_dir, env_flags, 0);
|
||
if (ret != 0) {
|
||
fprintf(stderr, "Error opening environment: %s\n",
|
||
db_strerror(ret));
|
||
goto err;
|
||
}
|
||
|
||
...
|
||
/*
|
||
* All other operations are identical from here. Notice, however,
|
||
* that we have not created any other threads of control before
|
||
* recovery is complete. You want to run recovery for
|
||
* the first thread in your application that opens an environment,
|
||
* but not for any subsequent threads.
|
||
*/ </pre>
|
||
</div>
|
||
</div>
|
||
<div class="navfooter">
|
||
<hr />
|
||
<table width="100%" summary="Navigation footer">
|
||
<tr>
|
||
<td width="40%" align="left"><a accesskey="p" href="backuprestore.html">Prev</a> </td>
|
||
<td width="20%" align="center">
|
||
<a accesskey="u" href="filemanagement.html">Up</a>
|
||
</td>
|
||
<td width="40%" align="right"> <a accesskey="n" href="architectrecovery.html">Next</a></td>
|
||
</tr>
|
||
<tr>
|
||
<td width="40%" align="left" valign="top">Backup Procedures </td>
|
||
<td width="20%" align="center">
|
||
<a accesskey="h" href="index.html">Home</a>
|
||
</td>
|
||
<td width="40%" align="right" valign="top"> Designing Your Application for Recovery</td>
|
||
</tr>
|
||
</table>
|
||
</div>
|
||
</body>
|
||
</html>
|