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>1.2. Architectural Fundamentals</A
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>    Before we proceed, you should understand the basic
    <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> system architecture.
    Understanding how the parts of
    <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> interact will make this
    chapter somewhat clearer.
   </P
><P
>    In database jargon, <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> uses a
    client/server model.  A <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
>
    session consists of the following cooperating processes
    (programs):

    <P
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><P
>       A server process, which manages the database files, accepts
       connections to the database from client applications, and
       performs database actions on behalf of the clients.  The
       database server program is called
       <TT
CLASS="FILENAME"
>postgres</TT
>.
       
      </P
></LI
><LI
><P
>       The user's client (frontend) application that wants to perform
       database operations.  Client applications can be very diverse
       in nature:  a client could be a text-oriented tool, a graphical
       application, a web server that accesses the database to
       display web pages, or a specialized database maintenance tool.
       Some client applications are supplied with the
       <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> distribution; most are
       developed by users.
      </P
></LI
></UL
><P>
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><P
>    As is typical of client/server applications, the client and the
    server can be on different hosts.  In that case they communicate
    over a TCP/IP network connection.  You should keep this in mind,
    because the files that can be accessed on a client machine might
    not be accessible (or might only be accessible using a different
    file name) on the database server machine.
   </P
><P
>    The <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> server can handle
    multiple concurrent connections from clients.  To achieve this it
    starts (<SPAN
CLASS="QUOTE"
>"forks"</SPAN
>) a new process for each connection.
    From that point on, the client and the new server process
    communicate without intervention by the original
    <TT
CLASS="FILENAME"
>postgres</TT
> process.  Thus, the
    master server process is always running, waiting for
    client connections, whereas client and associated server processes
    come and go.  (All of this is of course invisible to the user.  We
    only mention it here for completeness.)
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