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550 lines
21 KiB
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<?xml version="1.0" encoding="UTF-8" standalone="no"?>
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml">
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
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<title>Adding the Replication Manager to SimpleTxn</title>
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<link rel="stylesheet" href="gettingStarted.css" type="text/css" />
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<meta name="generator" content="DocBook XSL Stylesheets V1.73.2" />
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<link rel="start" href="index.html" title="Getting Started with Replicated Berkeley DB Applications" />
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<link rel="up" href="repapp.html" title="Chapter 3. The DB Replication Manager" />
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<link rel="prev" href="repapp.html" title="Chapter 3. The DB Replication Manager" />
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<link rel="next" href="fwrkpermmessage.html" title="Permanent Message Handling" />
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</head>
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<body>
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<div xmlns="" class="navheader">
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<div class="libver">
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<p>Library Version 11.2.5.2</p>
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</div>
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<table width="100%" summary="Navigation header">
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<tr>
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<th colspan="3" align="center">Adding the Replication Manager to
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<span xmlns="http://www.w3.org/1999/xhtml">SimpleTxn</span>
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</th>
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</tr>
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<tr>
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<td width="20%" align="left"><a accesskey="p" href="repapp.html">Prev</a> </td>
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<th width="60%" align="center">Chapter 3. The DB Replication Manager</th>
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<td width="20%" align="right"> <a accesskey="n" href="fwrkpermmessage.html">Next</a></td>
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</tr>
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</table>
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<hr />
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</div>
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<div class="sect1" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h2 class="title" style="clear: both"><a id="repmgr_init_example_c"></a>Adding the Replication Manager to
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<span>SimpleTxn</span>
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</h2>
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</div>
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</div>
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</div>
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<p>
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We now use the methods described above to add partial
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support to the
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<span>SimpleTxn</span>
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example that we presented in
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<a class="xref" href="txnapp.html" title="Chapter 2. Transactional Application">Transactional Application</a>.
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That is, in this section we will:
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</p>
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<div class="itemizedlist">
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<ul type="disc">
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<li>
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<p>
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Enhance our command line options to accept information
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of interest to a replicated application.
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</p>
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</li>
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<li>
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<p>
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Configure our environment handle to use replication and
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the Replication Manager.
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</p>
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</li>
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<li>
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<p>
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Minimally configure the Replication Manager.
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</p>
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</li>
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<li>
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<p>
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Start replication.
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</p>
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</li>
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</ul>
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</div>
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<p>
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Note that when we are done with this section, we will be
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only partially ready to run the application. Some critical
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pieces will be missing; specifically, we will not yet be
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handling the differences between a master and a
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replica. (We do that in the next chapter).
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</p>
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<p>
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Also, note that in the following code fragments, additions
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and changes to the code are marked in <strong class="userinput"><code>bold</code></strong>.
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</p>
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<p>
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To begin, we make some significant changes to our
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<code class="classname">RepConfig</code> class because we will be
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using it to maintain a lot more information that we needed
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for our simple transactional example.
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</p>
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<p>
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We begin by importing a few new
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classes. <code class="classname">java.util.Vector</code> is used to
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organize a list of "other host" definitions (that is, the host and
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port information for the other replication participants known to
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this application). We also need a couple of classes used to manage
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individual host and port information, as well as replication
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sites and startup policy information.
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</p>
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<pre class="programlisting"><strong class="userinput"><code>package db.repquote_gsg;
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import java.util.Vector;
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import com.sleepycat.db.ReplicationHostAddress;
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import com.sleepycat.db.ReplicationManagerSiteConfig;
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import com.sleepycat.db.ReplicationManagerStartPolicy;</code></strong>
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public class RepConfig
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{ </pre>
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<p>
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Next we add considerably to the constants and data members used by
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this class. All of this is used to manage information necessary for
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replication purposes. We also at this point change the program's
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name, since we will be doing that to the main class in our
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application a little later in this description.
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</p>
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<pre class="programlisting"> // Constant values used in the RepQuote application.
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public static final String progname = <strong class="userinput"><code>"RepQuoteExampleGSG";</code></strong>
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public static final int CACHESIZE = 10 * 1024 * 1024;
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<strong class="userinput"><code>public static final int SLEEPTIME = 5000;</code></strong>
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// member variables containing configuration information
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// String specifying the home directory for rep files.
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public String home;
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// Stores an optional set of "other" hosts.
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<strong class="userinput"><code>public Vector<ReplicationHostAddress> otherHosts;
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// Priority within the replication group.
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public int priority;
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public ReplicationManagerStartPolicy startPolicy;
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// The host address to listen to.
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public ReplicationHostAddress thisHost;
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// member variables used internally.
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private int currOtherHost;
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private boolean gotListenAddress;</code></strong></pre>
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<p>
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Now we update our class constructor to initialize all of these new
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variables:
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</p>
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<pre class="programlisting"> public RepConfig()
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{
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<strong class="userinput"><code>startPolicy = ReplicationManagerStartPolicy.REP_ELECTION;</code></strong>
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home = "TESTDIR";
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<strong class="userinput"><code>gotListenAddress = false;
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priority = 100;
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currOtherHost = 0;
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thisHost = new ReplicationManagerSiteConfig();
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otherHosts = new Vector();</code></strong>
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} </pre>
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<p>
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Finally, we finish updating this class by providing a series of new
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getter and setter methods. These are used primarily for setting a
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retrieving host information of interest to our replicated
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application:
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</p>
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<pre class="programlisting"> public java.io.File getHome()
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{
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return new java.io.File(home);
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}
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<strong class="userinput"><code>public void setThisHost(String host, int port, boolean creator)
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{
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gotListenAddress = true;
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thisHost.setHost(host);
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thisPort.setPort(port);
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thisHost.setGroupCreator(creator);
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}
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public ReplicationManagerSiteConfig getThisHost()
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{
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if (!gotListenAddress) {
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System.err.println("Warning: no host specified.");
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System.err.println("Returning default.");
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}
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return thisHost;
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}
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public ReplicationHostAddress getThisHostAddress()
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{
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if (!gotListenAddress) {
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System.err.println("Warning: no host specified.");
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System.err.println("Returning default.");
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}
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return thisHost.getAddress();
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}
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public boolean gotListenAddress() {
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return gotListenAddress;
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}
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public void addOtherHost(String host, int port)
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{
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ReplicationHostAddress newInfo =
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new ReplicationHostAddress(host, port);
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otherHosts.add(newInfo);
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}
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public ReplicationHostAddress getFirstOtherHost()
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{
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currOtherHost = 0;
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if (otherHosts.size() == 0)
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return null;
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return (ReplicationHostAddress)otherHosts.get(currOtherHost);
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}
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public ReplicationHostAddress getNextOtherHost()
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{
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currOtherHost++;
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if (currOtherHost >= otherHosts.size())
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return null;
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return (ReplicationHostAddress)otherHosts.get(currOtherHost);
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}
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public ReplicationHostAddress getOtherHost(int i)
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{
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if (i >= otherHosts.size())
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return null;
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return (ReplicationHostAddress)otherHosts.get(i);
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}</code></strong>
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} </pre>
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<p>
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Having completed our update to the
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<code class="classname">RepConfig</code>
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class, we can now start making
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changes to the main portion of our program. We begin by changing
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the program's name. <span>(This, of course, means that we copy our
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<code class="classname">SimpleTxn</code> code to a file named <code class="literal">RepQuoteExampleGSG.java</code>.)</span>
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</p>
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<pre class="programlisting">package db.repquote_gsg;
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import java.io.FileNotFoundException;
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import java.io.BufferedReader;
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import java.io.InputStreamReader;
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import java.io.IOException;
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import java.io.UnsupportedEncodingException;
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<strong class="userinput"><code>import java.lang.Thread;
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import java.lang.InterruptedException;</code></strong>
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import com.sleepycat.db.Cursor;
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import com.sleepycat.db.Database;
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import com.sleepycat.db.DatabaseConfig;
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import com.sleepycat.db.DatabaseEntry;
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import com.sleepycat.db.DatabaseException;
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import com.sleepycat.db.DatabaseType;
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import com.sleepycat.db.EnvironmentConfig;
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import com.sleepycat.db.LockMode;
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import com.sleepycat.db.OperationStatus;
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<strong class="userinput"><code>import com.sleepycat.db.ReplicationHostAddress;
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import com.sleepycat.db.ReplicationManagerSiteConfig;</code></strong>
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import db.repquote.RepConfig;
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public class <strong class="userinput"><code>RepQuoteExampleGSG</code></strong>
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{
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private RepConfig repConfig;
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private Environment dbenv; </pre>
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<p>
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Next we update our usage function. The application will continue to
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accept the <code class="literal">-h</code> parameter so that we can identify
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the environment home directory used by this application. However,
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we also add the:
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</p>
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<div class="itemizedlist">
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<ul type="disc">
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<li>
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<p>
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<code class="literal">-l</code> parameter which allows us to identify the
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host and port used by this application to listen for
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replication messages. This parameter is required unless the -L
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parameter is specified.
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</p>
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</li>
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<li>
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<p>
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<code class="literal">-L</code> parameter, which allows us to identify
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the local site as the group creator.
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</p>
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</li>
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<li>
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<p>
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<code class="literal">-r</code> parameter which allows us to specify
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other replicas.
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</p>
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</li>
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<li>
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<p>
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<code class="literal">-p</code> option, which is used to identify this
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replica's priority (recall that the priority is used as a tie
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breaker for elections)
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</p>
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</li>
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</ul>
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</div>
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<pre class="programlisting">
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public <strong class="userinput"><code>RepQuoteExampleGSG()</code></strong>
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throws DatabaseException
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{
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repConfig = null;
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dbenv = null;
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}
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public static void usage()
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{
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System.err.println("usage: " + repConfig.progname);
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System.err.println("-h home<strong class="userinput"><code>[-r host:port][-l|-L host:port]" +
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"[-r host:port][-p priority]</code></strong>");
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System.err.println("\t -h home directory (required)\n" +
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<strong class="userinput"><code>"\t -l host:port (required, unless -L is specified; " +
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"l stands for local)\n" +
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"\t -L host:port (optional;L mean group creator)\n" +
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"\t -r host:port (optional; r stands for remote; any " +
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"number of these may be specified)\n" +
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"\t -p priority (optional: defaults to 100)\n");</code></strong>
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System.exit(1);
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} </pre>
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<p>
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Now we can begin working on our <code class="literal">main()</code> function.
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We begin by adding a couple of variables that we will use to
|
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collect TCP/IP host and port information.
|
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|
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|
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|
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|
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|
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</p>
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|
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<pre class="programlisting"> public static void main(String[] argv)
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|
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throws Exception
|
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|
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{
|
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|
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RepConfig config = new RepConfig();
|
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|
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<strong class="userinput"><code>String tmpHost;
|
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|
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int tmpPort = 0;</code></strong> </pre>
|
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|
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<p>
|
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|
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Now we collect our command line arguments. As we do so, we will
|
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|
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configure host and port information as required, and we will
|
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|
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configure the application's election priority if necessary.
|
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|
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</p>
|
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|
|
<pre class="programlisting"> // Extract the command line parameters
|
|||
|
|
for (int i = 0; i < argv.length; i++)
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|
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{
|
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if (argv[i].compareTo("-h") == 0) {
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|
|
// home is a string arg.
|
|||
|
|
i++;
|
|||
|
|
config.home = argv[i];
|
|||
|
|
<strong class="userinput"><code>} else if (argv[i].compareTo("-l") == 0) ||
|
|||
|
|
argv[i].compareTo("-L") == 0) {
|
|||
|
|
if (i == argv.length - 1)
|
|||
|
|
usage();
|
|||
|
|
if (argv[i].compareTo("-L") == 0)
|
|||
|
|
isCreator = true;
|
|||
|
|
// "local" should be host:port.
|
|||
|
|
i++;
|
|||
|
|
String[] words = argv[i].split(":");
|
|||
|
|
if (words.length != 2) {
|
|||
|
|
System.err.println(
|
|||
|
|
"Invalid host specification host:port needed.");
|
|||
|
|
usage();
|
|||
|
|
}
|
|||
|
|
try {
|
|||
|
|
tmpPort = Integer.parseInt(words[1]);
|
|||
|
|
} catch (NumberFormatException nfe) {
|
|||
|
|
System.err.println("Invalid host specification, " +
|
|||
|
|
"could not parse port number.");
|
|||
|
|
usage();
|
|||
|
|
}
|
|||
|
|
config.setThisHost(words[0], tmpPort, isCreator);
|
|||
|
|
} else if (argv[i].compareTo("-p") == 0) {
|
|||
|
|
i++;
|
|||
|
|
config.priority = Integer.parseInt(argv[i]);
|
|||
|
|
} else if (argv[i].compareTo("-r") == 0) {
|
|||
|
|
i++;
|
|||
|
|
String[] words = argv[i].split(":");
|
|||
|
|
if (words.length != 2) {
|
|||
|
|
System.err.println(
|
|||
|
|
"Invalid host specification host:port needed.");
|
|||
|
|
usage();
|
|||
|
|
}
|
|||
|
|
try {
|
|||
|
|
tmpPort = Integer.parseInt(words[1]);
|
|||
|
|
} catch (NumberFormatException nfe) {
|
|||
|
|
System.err.println("Invalid host specification, " +
|
|||
|
|
"could not parse port number.");
|
|||
|
|
usage();
|
|||
|
|
}
|
|||
|
|
config.addOtherHost(words[0], tmpPort);
|
|||
|
|
}</code></strong> else {
|
|||
|
|
System.err.println("Unrecognized option: " + argv[i]);
|
|||
|
|
usage();
|
|||
|
|
}
|
|||
|
|
}
|
|||
|
|
|
|||
|
|
// Error check command line.
|
|||
|
|
if (<strong class="userinput"><code>(!config.gotListenAddress())</code></strong> || config.home.length() == 0)
|
|||
|
|
usage(); </pre>
|
|||
|
|
<p>
|
|||
|
|
Having done that, the remainder of our <code class="function">main()</code>
|
|||
|
|
function is left unchanged, with the exception of a few name changes required by the
|
|||
|
|
new class name:
|
|||
|
|
</p>
|
|||
|
|
<pre class="programlisting"> <strong class="userinput"><code>RepQuoteExampleGSG</code></strong> runner = null;
|
|||
|
|
try {
|
|||
|
|
runner = new <strong class="userinput"><code>RepQuoteExampleGSG();</code></strong>
|
|||
|
|
runner.init(config);
|
|||
|
|
|
|||
|
|
runner.doloop();
|
|||
|
|
runner.terminate();
|
|||
|
|
} catch (DatabaseException dbe) {
|
|||
|
|
System.err.println("Caught an exception during " +
|
|||
|
|
"initialization or processing: " + dbe.toString());
|
|||
|
|
if (runner != null)
|
|||
|
|
runner.terminate();
|
|||
|
|
}
|
|||
|
|
System.exit(0);
|
|||
|
|
} // end main </pre>
|
|||
|
|
<p>
|
|||
|
|
Now we need to update our
|
|||
|
|
|
|||
|
|
<code class="methodname">RepQuoteExampleGSG.init()</code>
|
|||
|
|
method. Our updates are at first related to configuring
|
|||
|
|
replication. First, we need to update the method so that we can
|
|||
|
|
identify the local site to the environment handle (that is, the site identified by the
|
|||
|
|
<code class="literal">-l</code> command line option):
|
|||
|
|
</p>
|
|||
|
|
<pre class="programlisting"> public int init(RepConfig config)
|
|||
|
|
throws DatabaseException
|
|||
|
|
{
|
|||
|
|
int ret = 0;
|
|||
|
|
repConfig = config;
|
|||
|
|
EnvironmentConfig envConfig = new EnvironmentConfig();
|
|||
|
|
envConfig.setErrorStream(System.err);
|
|||
|
|
envConfig.setErrorPrefix(RepConfig.progname);
|
|||
|
|
|
|||
|
|
<strong class="userinput"><code>envConfig.addReplicationManagerSite(repConfig.getThisHost());</code></strong> </pre>
|
|||
|
|
<p>
|
|||
|
|
And we also add code to allow us to identify "other" sites to the
|
|||
|
|
environment handle (that is, the sites that we identify using the
|
|||
|
|
<code class="literal">-o</code> command line option). To do this, we iterate over
|
|||
|
|
each of the "other" sites provided to us using the
|
|||
|
|
<code class="literal">-o</code> command line option, and we add each one
|
|||
|
|
individually in turn:
|
|||
|
|
</p>
|
|||
|
|
<p>
|
|||
|
|
We also add code here to set the environment's priority.
|
|||
|
|
</p>
|
|||
|
|
<pre class="programlisting"> <strong class="userinput"><code>
|
|||
|
|
for (ReplicationHostAddress host =
|
|||
|
|
repConfig.getFirstOtherHost(); host != null;
|
|||
|
|
host = repConfig.getNextOtherHost()) {
|
|||
|
|
|
|||
|
|
ReplicationManagerSiteConfig repmgrRemoteSiteConfig =
|
|||
|
|
new ReplicationManagerSiteConfig(host.host, host.port);
|
|||
|
|
repmgrRemoteSiteConfig.setBootstrapHelper(true);
|
|||
|
|
envConfig.addReplicationManagerSite(
|
|||
|
|
repmgrRemoteSiteConfig);
|
|||
|
|
}
|
|||
|
|
|
|||
|
|
envConfig.addReplicationPriority(repConfig.priority);
|
|||
|
|
</code></strong> </pre>
|
|||
|
|
<p>
|
|||
|
|
|
|||
|
|
|
|||
|
|
|
|||
|
|
|
|||
|
|
<span>We can now open our environment. Note that the options</span>
|
|||
|
|
|
|||
|
|
we use to open the environment are slightly different for a
|
|||
|
|
replicated application than they are for a non-replicated
|
|||
|
|
application. Namely, replication requires the
|
|||
|
|
|
|||
|
|
|
|||
|
|
<span>
|
|||
|
|
<code class="methodname">EnvironmentConfig.setInitializeReplication()</code> option.
|
|||
|
|
</span>
|
|||
|
|
</p>
|
|||
|
|
<p>
|
|||
|
|
Also, because we are using the Replication Manager, we must prepare
|
|||
|
|
our environment for threaded usage. For this reason, we also
|
|||
|
|
need the <code class="literal">DB_THREAD</code> flag.
|
|||
|
|
</p>
|
|||
|
|
<pre class="programlisting"> envConfig.setCacheSize(RepConfig.CACHESIZE);
|
|||
|
|
envConfig.setTxnNoSync(true);
|
|||
|
|
|
|||
|
|
envConfig.setAllowCreate(true);
|
|||
|
|
envConfig.setRunRecovery(true);
|
|||
|
|
<strong class="userinput"><code>envConfig.setInitializeReplication(true);</code></strong>
|
|||
|
|
envConfig.setInitializeLocking(true);
|
|||
|
|
envConfig.setInitializeLogging(true);
|
|||
|
|
envConfig.setInitializeCache(true);
|
|||
|
|
envConfig.setTransactional(true);
|
|||
|
|
try {
|
|||
|
|
dbenv = new Environment(appConfig.getHome(), envConfig);
|
|||
|
|
} catch(FileNotFoundException e) {
|
|||
|
|
System.err.println("FileNotFound exception: " + e.toString());
|
|||
|
|
System.err.println(
|
|||
|
|
"Ensure that the environment directory is pre-created.");
|
|||
|
|
ret = 1;
|
|||
|
|
} </pre>
|
|||
|
|
<p>
|
|||
|
|
Finally, we start replication before we exit this method.
|
|||
|
|
Immediately after exiting this method, our application will go into
|
|||
|
|
the
|
|||
|
|
|
|||
|
|
<code class="methodname">RepQuoteExampleGSG.doloop()</code>
|
|||
|
|
method, which is where
|
|||
|
|
the bulk of our application's work is performed. We update that
|
|||
|
|
method in the next chapter.
|
|||
|
|
</p>
|
|||
|
|
<pre class="programlisting"> // start Replication Manager
|
|||
|
|
dbenv.replicationManagerStart(3, appConfig.startPolicy);
|
|||
|
|
return ret;
|
|||
|
|
} </pre>
|
|||
|
|
<p>
|
|||
|
|
This completes our replication updates for the moment. We are not as
|
|||
|
|
yet ready to actually run this program; there remains a few
|
|||
|
|
critical pieces left to add to it. However, the work that we
|
|||
|
|
performed in this section represents a solid foundation for the
|
|||
|
|
remainder of our replication work.
|
|||
|
|
</p>
|
|||
|
|
</div>
|
|||
|
|
<div class="navfooter">
|
|||
|
|
<hr />
|
|||
|
|
<table width="100%" summary="Navigation footer">
|
|||
|
|
<tr>
|
|||
|
|
<td width="40%" align="left"><a accesskey="p" href="repapp.html">Prev</a> </td>
|
|||
|
|
<td width="20%" align="center">
|
|||
|
|
<a accesskey="u" href="repapp.html">Up</a>
|
|||
|
|
</td>
|
|||
|
|
<td width="40%" align="right"> <a accesskey="n" href="fwrkpermmessage.html">Next</a></td>
|
|||
|
|
</tr>
|
|||
|
|
<tr>
|
|||
|
|
<td width="40%" align="left" valign="top">Chapter 3. The DB Replication Manager </td>
|
|||
|
|
<td width="20%" align="center">
|
|||
|
|
<a accesskey="h" href="index.html">Home</a>
|
|||
|
|
</td>
|
|||
|
|
<td width="40%" align="right" valign="top"> Permanent Message Handling</td>
|
|||
|
|
</tr>
|
|||
|
|
</table>
|
|||
|
|
</div>
|
|||
|
|
</body>
|
|||
|
|
</html>
|