mirror of
https://github.com/yasuhirokimura/db18
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Yasuhiro KIMURA
121 lines
5.9 KiB
HTML
121 lines
5.9 KiB
HTML
<?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>Ex_rep_base: putting it all together</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="Berkeley DB Programmer's Reference Guide" />
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<link rel="up" href="rep.html" title="Chapter 12. Berkeley DB Replication" />
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<link rel="prev" href="rep_ex_comm.html" title="Ex_rep_base: a TCP/IP based communication infrastructure" />
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<link rel="next" href="rep_ex_chan.html" title="Ex_rep_chan: a Replication Manager channel example" />
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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 18.1.40</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">Ex_rep_base: putting it all
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together</th>
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</tr>
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<tr>
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<td width="20%" align="left"><a accesskey="p" href="rep_ex_comm.html">Prev</a> </td>
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<th width="60%" align="center">Chapter 12. Berkeley DB Replication </th>
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<td width="20%" align="right"> <a accesskey="n" href="rep_ex_chan.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="rep_ex_rq"></a>Ex_rep_base: putting it all
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together</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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Beyond simply initializing a replicated environment, a Base
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API application must set up its communication infrastructure,
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and then make sure that incoming messages are received and
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processed.
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</p>
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<p>
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To initialize replication, ex_rep_base creates a Berkeley DB
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environment and calls <a href="../api_reference/C/reptransport.html" class="olink">DB_ENV->rep_set_transport()</a> to establish a send
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function. (See the main function in
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<code class="filename">ex_rep/base/rep_base.c</code>, including its
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calls to the create_env and env_init functions in
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<code class="filename">ex_rep/common/rep_common.c</code>.)
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</p>
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<p>
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ex_rep_base opens a listening socket for incoming
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connections and opens an outgoing connection to every machine
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that it knows about (that is, all the sites listed in the
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<span class="bold"><strong>-r</strong></span> and <span class="bold"><strong>-R</strong></span> command line arguments).
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Applications can structure the details of this in different
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ways, but ex_rep_base creates a user-level thread to listen on
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its socket, plus a thread to loop and handle messages on each
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socket, in addition to the threads needed to manage the user
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interface, update the database on the master, and read from
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the database on the client (in other words, in addition to the
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normal functionality of any database application).
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</p>
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<p>
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Once the initial threads have all been started and the
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communications infrastructure is initialized, the application
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signals that it is ready for replication and joins a
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replication group by calling <a href="../api_reference/C/repstart.html" class="olink">DB_ENV->rep_start()</a>. (Again, see the main
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function in
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<code class="filename">ex_rep/base/rep_base.c</code>.)
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</p>
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<p>
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Note the use of the optional second argument to <a href="../api_reference/C/repstart.html" class="olink">DB_ENV->rep_start()</a>
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in the client initialization code. The argument "local" is a
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piece of data, opaque to Berkeley DB, that will be broadcast
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to each member of a replication group; it allows new clients
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to join a replication group, without knowing the location of
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all its members; the new client will be contacted by the
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members it does not know about, who will receive the new
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client's contact information that was specified in "myaddr."
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See <a class="xref" href="rep_newsite.html" title="Connecting to a new site">Connecting to a new site</a>
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for more information.
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</p>
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<p>
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The final piece of a replicated application is the code that
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loops, receives, and processes messages from a given remote
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environment. ex_rep_base runs one of these loops in a parallel
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thread for each socket connection (see the hm_loop function in
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<code class="filename">ex_rep/base/rep_msg.c</code>). Other
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applications may want to queue messages somehow and process
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them asynchronously, or select() on a number of sockets and
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either look up the correct environment ID for each or
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encapsulate the ID in the communications protocol.
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</p>
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</div>
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<div class="navfooter">
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<hr />
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<table width="100%" summary="Navigation footer">
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<tr>
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<td width="40%" align="left"><a accesskey="p" href="rep_ex_comm.html">Prev</a> </td>
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<td width="20%" align="center">
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<a accesskey="u" href="rep.html">Up</a>
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</td>
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<td width="40%" align="right"> <a accesskey="n" href="rep_ex_chan.html">Next</a></td>
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</tr>
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<tr>
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<td width="40%" align="left" valign="top">Ex_rep_base: a TCP/IP based communication infrastructure </td>
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<td width="20%" align="center">
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<a accesskey="h" href="index.html">Home</a>
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</td>
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<td width="40%" align="right" valign="top"> Ex_rep_chan: a Replication Manager channel example</td>
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</tr>
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</table>
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</div>
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</body>
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</html>
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