mirror of
https://github.com/berkeleydb/je.git
synced 2024-07-06 18:07:18 +00:00
158 lines
7 KiB
HTML
158 lines
7 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>Opening a Replicated Environment</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, Java Edition High Availability Applications" />
|
||
<link rel="up" href="progoverview.html" title="Chapter 2. Replication API First Steps" />
|
||
<link rel="prev" href="exceptions.html" title="HA Exceptions" />
|
||
<link rel="next" href="replicawrites.html" title="Managing Write Requests at a Replica" />
|
||
</head>
|
||
<body>
|
||
<div xmlns="" class="navheader">
|
||
<div class="libver">
|
||
<p>Library Version 12.2.7.5</p>
|
||
</div>
|
||
<table width="100%" summary="Navigation header">
|
||
<tr>
|
||
<th colspan="3" align="center">Opening a Replicated Environment</th>
|
||
</tr>
|
||
<tr>
|
||
<td width="20%" align="left"><a accesskey="p" href="exceptions.html">Prev</a> </td>
|
||
<th width="60%" align="center">Chapter 2. Replication API First Steps</th>
|
||
<td width="20%" align="right"> <a accesskey="n" href="replicawrites.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="repenvironmentopen"></a>Opening a Replicated Environment</h2>
|
||
</div>
|
||
</div>
|
||
</div>
|
||
<p>
|
||
In the previous two sections we looked at the basics of how to create a
|
||
replicated environment, and what exceptions you can expect to see in a JE HA
|
||
application. Now we need to combine these two topics in order to examine how you should
|
||
open a <a class="ulink" href="../java/com/sleepycat/je/rep/ReplicatedEnvironment.html" target="_top">ReplicatedEnvironment</a> handle to an existing replicated
|
||
environment.
|
||
</p>
|
||
<p>
|
||
When you open the handle, the underlying HA code will attempt to open a TCP/IP
|
||
connection to other nodes in the replication group, based on the node's stored
|
||
replication group metadata or the helper host information that you provide. In doing so,
|
||
the node will attempt to locate a Master or, failing that, will hold an election in order
|
||
to select a new Master, if it is an electable node.
|
||
</p>
|
||
<p>
|
||
Due to issues of timing and network performance, the node may or may not be able to:
|
||
</p>
|
||
<div class="orderedlist">
|
||
<ol type="1">
|
||
<li>
|
||
<p>
|
||
locate the master; and
|
||
</p>
|
||
</li>
|
||
<li>
|
||
<p>
|
||
hold an election.
|
||
</p>
|
||
</li>
|
||
</ol>
|
||
</div>
|
||
<p>
|
||
This can happen if there simply are not enough electable nodes available in order for the current
|
||
node to start up, find the current master, or hold an election. Remember that a majority
|
||
of the electable nodes registered in the replication group must be available in order to hold an
|
||
election.
|
||
</p>
|
||
<p>
|
||
If this situation occurs, the <a class="ulink" href="../java/com/sleepycat/je/rep/ReplicatedEnvironment.html" target="_top">ReplicatedEnvironment</a> constructor will throw an
|
||
<a class="ulink" href="../java/com/sleepycat/je/rep/UnknownMasterException.html" target="_top">UnknownMasterException</a>. Therefore, typically, it is best that you prepare for this
|
||
situation by performing the handle creation in a retry loop, as shown in the following
|
||
code snippet.
|
||
</p>
|
||
<p>
|
||
In addition, if the Replica has been down for a long enough
|
||
period of time, it might be so far out of date that it cannot
|
||
be brought up to date using the normal replication stream. In
|
||
this case, the <a class="ulink" href="../java/com/sleepycat/je/rep/ReplicatedEnvironment.html" target="_top">ReplicatedEnvironment</a> constructor will throw
|
||
an <a class="ulink" href="../java/com/sleepycat/je/rep/InsufficientLogException.html" target="_top">InsufficientLogException</a>. See <a class="xref" href="logfile-restore.html" title="Restoring Log Files">Restoring Log Files</a> for information on how to handle this
|
||
exception.
|
||
</p>
|
||
<pre class="programlisting">private static int REP_HANDLE_RETRY_MAX = 100;
|
||
|
||
...
|
||
|
||
ReplicatedEnvironment getEnvironment(File envHome, String groupName,
|
||
String nodeName, String nodeHost,
|
||
String helperHosts)
|
||
throws IllegalStateException, InterruptedException {
|
||
|
||
EnvironmentConfig envConfig = new EnvironmentConfig();
|
||
envConfig.setAllowCreate(true);
|
||
envConfig.setTransactional(true);
|
||
|
||
// Identify the node
|
||
ReplicationConfig repConfig =
|
||
new ReplicationConfig();
|
||
repConfig.setGroupName(groupName);
|
||
repConfig.setNodeName(nodeName);
|
||
repConfig.setNodeHostPort(nodeHost);
|
||
repConfig.setHelperHosts(helperHosts);
|
||
|
||
for (int i = 0; i < REP_HANDLE_RETRY_MAX; i++) {
|
||
try {
|
||
return new
|
||
ReplicatedEnvironment(envHome, repConfig, envConfig);
|
||
} catch (UnknownMasterException ume) {
|
||
/*
|
||
* Insert application specific code here to indicate that
|
||
* this problem was encountered, such as writing the
|
||
* condition to a log file.
|
||
*/
|
||
|
||
Thread.sleep(5 * 1000);
|
||
continue;
|
||
} catch (InsufficientLogException ile) {
|
||
/* A network restore is required, make the necessary calls */
|
||
}
|
||
|
||
}
|
||
throw new
|
||
IllegalStateException("getEnvironment: reached max retries");
|
||
} </pre>
|
||
<p>
|
||
Note that for production code, you may want to retry the handle open without any maximum
|
||
retry limit.
|
||
</p>
|
||
</div>
|
||
<div class="navfooter">
|
||
<hr />
|
||
<table width="100%" summary="Navigation footer">
|
||
<tr>
|
||
<td width="40%" align="left"><a accesskey="p" href="exceptions.html">Prev</a> </td>
|
||
<td width="20%" align="center">
|
||
<a accesskey="u" href="progoverview.html">Up</a>
|
||
</td>
|
||
<td width="40%" align="right"> <a accesskey="n" href="replicawrites.html">Next</a></td>
|
||
</tr>
|
||
<tr>
|
||
<td width="40%" align="left" valign="top">HA Exceptions </td>
|
||
<td width="20%" align="center">
|
||
<a accesskey="h" href="index.html">Home</a>
|
||
</td>
|
||
<td width="40%" align="right" valign="top"> Managing Write Requests at a Replica</td>
|
||
</tr>
|
||
</table>
|
||
</div>
|
||
</body>
|
||
</html>
|