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77 lines
3.2 KiB
HTML
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<TITLE>The POSTGRES95 User Manual - ARCHITECTURE</TITLE>
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<font size=-1>
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<A HREF="pg95user.html">[ TOC ]</A>
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<H1>2. POSTGRES ARCHITECTURE CONCEPTS</H1>
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<HR>
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Before we continue, you should understand the basic
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POSTGRES system architecture. Understanding how the
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parts of POSTGRES interact will make the next chapter
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somewhat clearer.
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In database jargon, POSTGRES uses a simple "process
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per-user" client/server model. A POSTGRES session
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consists of the following cooperating UNIX processes (programs):
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<UL>
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<LI>A supervisory daemon process (the <B>postmaster</B>),
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<LI>the user's frontend application (e.g., the <B>psql</B> program), and
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<LI>the one or more backend database servers (the <B>postgres</B> process itself).
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</UL>
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A single <B>postmaster</B> manages a given collection of
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databases on a single host. Such a collection of
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databases is called an installation or site. Frontend
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applications that wish to access a given database
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within an installation make calls to the library.
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The library sends user requests over the network to the
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<B>postmaster</B> (Figure 1(a)), which in turn starts a new
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backend server process (Figure 1(b))
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<IMG SRC="figure01.gif" ALIGN=right ALT="Figure 1- How a connection is established"><br>
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and connects the
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frontend process to the new server (Figure 1(c)). From
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that point on, the frontend process and the backend
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server communicate without intervention by the
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<B>postmaster</B>. Hence, the <B>postmaster</B> is always running, waiting
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for requests, whereas frontend and backend processes
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come and go. The <B>LIBPQ</B> library allows a single
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frontend to make multiple connections to backend processes.
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However, the frontend application is still a
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single-threaded process. Multithreaded frontend/backend
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connections are not currently supported in <B>LIBPQ</B>.
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One implication of this architecture is that the
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<B>postmaster</B> and the backend always run on the same
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machine (the database server), while the frontend
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application may run anywhere. You should keep this
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in mind,
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because the files that can be accessed on a client
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machine may not be accessible (or may only be accessed
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using a different filename) on the database server
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machine.
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You should also be aware that the <B>postmaster</B> and
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postgres servers run with the user-id of the POSTGRES
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"superuser." Note that the POSTGRES superuser does not
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have to be a special user (e.g., a user named
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"postgres"). Furthermore, the POSTGRES superuser
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should
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definitely not be the UNIX superuser, "root"! In any
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case, all files relating to a database should belong to
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this POSTGRES superuser.
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<HR>
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<font size=-1>
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<A HREF="pg95user.html">[ TOC ]</A>
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<A HREF="intro.html">[ Previous ]</A>
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<A HREF="start.html">[ Next ]</A>
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</font>
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