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<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="sect1" lang="en">
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<div class="titlepage"><div><div><h2 class="title" style="clear: both">
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<a name="tutorial-arch"></a>1.2.�Architectural Fundamentals</h2></div></div></div>
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<p> Before we proceed, you should understand the basic
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<span class="productname">PostgreSQL</span> system architecture.
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Understanding how the parts of
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<span class="productname">PostgreSQL</span> interact will make this
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chapter somewhat clearer.
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<p> In database jargon, <span class="productname">PostgreSQL</span> uses a
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client/server model. A <span class="productname">PostgreSQL</span>
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session consists of the following cooperating processes
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<div class="itemizedlist"><ul type="disc">
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<li><p> A server process, which manages the database files, accepts
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connections to the database from client applications, and
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performs actions on the database on behalf of the clients. The
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database server program is called
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<code class="filename">postmaster</code>.
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<a name="id556983"></a>
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<li><p> The user's client (frontend) application that wants to perform
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database operations. Client applications can be very diverse
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in nature: a client could be a text-oriented tool, a graphical
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application, a web server that accesses the database to
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display web pages, or a specialized database maintenance tool.
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Some client applications are supplied with the
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<span class="productname">PostgreSQL</span> distribution; most are
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<p> As is typical of client/server applications, the client and the
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server can be on different hosts. In that case they communicate
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over a TCP/IP network connection. You should keep this in mind,
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because the files that can be accessed on a client machine might
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not be accessible (or might only be accessible using a different
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file name) on the database server machine.
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<p> The <span class="productname">PostgreSQL</span> server can handle
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multiple concurrent connections from clients. For that purpose it
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starts (“<span class="quote">forks</span>”) a new process for each connection.
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From that point on, the client and the new server process
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communicate without intervention by the original
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<code class="filename">postmaster</code> process. Thus, the
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<code class="filename">postmaster</code> is always running, waiting for
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client connections, whereas client and associated server processes
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come and go. (All of this is of course invisible to the user. We
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only mention it here for completeness.)
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