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<sect1 id="history">
 <title>A Short History of <productname>PostgreSQL</productname></title>

 <para>
  The object-relational database management system now known as 
  <productname>PostgreSQL</productname> (and briefly called
  <productname>Postgres95</productname>) is derived from the
  <productname>Postgres</productname> package written at the University of
  California at Berkeley.  With over a decade of
  development behind it, <productname>PostgreSQL</productname> 
  is the most advanced open-source database available anywhere,
  offering multiversion concurrency control, supporting almost
  all SQL constructs (including subselects, transactions, and
  user-defined types and functions), and having a wide range of
  language bindings available (including C, C++, Java, Perl, Tcl, and Python).
 </para>

 <sect2>
  <title>The Berkeley <productname>Postgres</productname> Project</title>

  <para>
   Implementation of the <productname>Postgres</productname> 
   <acronym>DBMS</acronym> began in 1986.  The
   initial  concepts  for  the  system  were  presented in
   <xref linkend="STON86">
   and the definition of the initial  data  model
   appeared in 
   <xref linkend="ROWE87">.
   The design of the rule system at
   that time was described in  
   <xref linkend="STON87a">.
   The  rationale
   and  architecture  of the storage manager were detailed in 
   <xref linkend="STON87b">.
  </para>

  <para>
   <productname>Postgres</productname> has undergone  several  major  releases  since
   then.   The  first <quote>demoware</quote> system became operational
   in 1987 and was shown at the  1988  <acronym>ACM-SIGMOD</acronym>  
   Conference.   Version 1, described in 
   <xref linkend="STON90a">, was released
   to a few external users in June 1989.  In response to a
   critique  of  the  first rule system 
   (<xref linkend="STON89">), 
   the rule
   system was  redesigned 
   (<xref linkend="STON90b">)
   and  Version  2  was
   released  in  June 1990 with the new rule system.  
   Version 3 appeared in 1991 and added support for  multiple
   storage  managers,  an  improved  query executor, and a
   rewritten rewrite rule  system.   For  the  most  part, subsequent
   releases  until <productname>Postgres95</productname> (see below)
   focused on portability and reliability.
  </para>

  <para>
   <productname>Postgres</productname> has been  used
   to  implement  many  different
   research and production applications.  These include: a
   financial data analysis system, a  jet  engine  
   performance   monitoring   package,   an   asteroid  tracking
   database, a medical information database,  and  several
   geographic information systems.  
   <productname>Postgres</productname> has also been
   used as an educational tool  at  several  universities.
   Finally,  
   <ulink url="http://www.illustra.com/">Illustra  Information  Technologies</ulink>
   (since merged into
   <ulink url="http://www.informix.com/"><productname>Informix</productname></ulink>)
   picked up
   the code and commercialized it.
   <productname>Postgres</productname>  became  the  primary  data  manager
   for  the
   <ulink url="http://www.sdsc.edu/0/Parts_Collabs/S2K/s2k_home.html">Sequoia 2000</ulink>
   scientific computing project in late 1992.
  </para>

  <para>
   The size of the  external  user  community
   nearly  doubled  during  1993.   It became increasingly
   obvious that maintenance of the prototype code and 
   support  was  taking  up large amounts of time that should
   have been devoted to database research.  In  an  effort
   to  reduce  this support burden, the Berkeley
   <productname>Postgres</productname> project officially
   ended with Version 4.2.
  </para>
 </sect2>

 <sect2>
  <title><productname>Postgres95</productname></title>

  <para>
   In 1994, Andrew Yu and Jolly Chen
   added a SQL language interpreter to <productname>Postgres</productname>.
   <productname>Postgres95</productname> was subsequently released to
   the Web to find its own way in the world as an
   open-source descendant of the original <productname>Postgres</productname>
   Berkeley code.
  </para>

  <para>
   <productname>Postgres95</productname> code was completely
   ANSI C and trimmed in size by 25%. Many
   internal changes improved performance and maintainability. 
   <productname>Postgres95</productname> v1.0.x ran about  30-50%
   faster  on  the  Wisconsin  Benchmark compared to 
   <productname>Postgres</productname> v4.2.
   Apart from bug fixes, these were the major enhancements:

   <itemizedlist>
    <listitem>
     <para>
      The query language <productname>Postquel</productname> was replaced with
      <acronym>SQL</acronym> (implemented in the server).
      Subqueries were not supported until
      <productname>PostgreSQL</productname> (see below), but they
      could be imitated in <productname>Postgres95</productname> with user-defined
      <acronym>SQL</acronym> functions. Aggregates were
      re-implemented.  Support for the GROUP BY query clause was also added.
      The <filename>libpq</filename> interface remained
      available  for  <acronym>C</acronym>  
      programs.
     </para>
    </listitem>

    <listitem>
     <para>
      In addition to the monitor program, a new program
      (<application>psql</application>) was provided for interactive SQL queries
      using <acronym>GNU</acronym> <application>Readline</application>.
     </para>
    </listitem>

    <listitem>
     <para>
      A new  front-end  library,  <filename>libpgtcl</filename>,
      supported  <acronym>Tcl</acronym>-based  clients.   A sample shell, 
      <command>pgtclsh</command>, provided new Tcl  commands  to  interface
      <application>Tcl</application>
      programs with the <productname>Postgres95</productname> backend.
     </para>
    </listitem>

    <listitem>
     <para>
      The  large  object interface was overhauled. The Inversion large objects were
      the  only  mechanism for  storing  large objects.
      (The Inversion file system was removed.)
     </para>
    </listitem>

    <listitem>
     <para>
      The  instance-level  rule  system  was removed.
      Rules were still available as rewrite rules.
     </para>
    </listitem>

    <listitem>
     <para>
      A short tutorial introducing regular <acronym>SQL</acronym> features as
      well as those of <productname>Postgres95</productname> was
      distributed with the source code
     </para>
    </listitem>

    <listitem>
     <para>
      <acronym>GNU</acronym> make (instead of  <acronym>BSD</acronym>  make)  was  used
      for  the build.  Also,  <productname>Postgres95</productname>  could  be
      compiled with an unpatched <productname>gcc</productname>
      (data alignment of  doubles  was fixed).
     </para>
    </listitem>
   </itemizedlist>
  </para>
 </sect2>

 <sect2>
  <title><productname>PostgreSQL</productname></title>

  <para>
   By 1996, it became clear that the name <quote>Postgres95</quote> would
   not stand the test of time. We chose a new name,
   <productname>PostgreSQL</productname>, to reflect the relationship
   between the original <productname>Postgres</productname> and the more
   recent versions with <acronym>SQL</acronym> capability.  At the same
   time, we set the version numbering to start at 6.0, putting the
   numbers back into the sequence originally begun by the
   <productname>Postgres</productname> Project.
  </para>

  <para>
   The emphasis during development of <productname>Postgres95</productname>
   was on identifying and understanding existing problems in the backend code.
   With <productname>PostgreSQL</productname>, 
   the emphasis has shifted to augmenting features and capabilities, although
   work continues in all areas.
  </para>

  <para>
   Major enhancements in <productname>PostgreSQL</productname> include:
  </para>

  <itemizedlist>
   <listitem>
    <para>
     Table-level locking has been replaced with multiversion concurrency control,
     which allows readers to continue reading consistent data during writer activity
     and enables hot backups from pg_dump while the database stays available for
     queries.
    </para>
   </listitem>

   <listitem>
    <para>
     Important backend features, including subselects, defaults, 
     constraints, and triggers, have been implemented.
    </para>
   </listitem>

   <listitem>
    <para>
     Additional <acronym>SQL92</acronym>-compliant language features have been added,
     including primary keys, quoted identifiers, literal string type coercion,
     type casting, and binary and hexadecimal integer input.
    </para>
   </listitem>

   <listitem>
    <para>
     Built-in types have been improved, including new wide-range date/time types 
     and additional geometric type support.
    </para>
   </listitem>

   <listitem>
    <para>
     Overall backend code speed has been increased by approximately 20-40%, 
     and backend start-up time has decreased 80% since version 6.0 was released.
    </para>
   </listitem>
  </itemizedlist>
 </sect2>
</sect1>

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