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<sect1 id="release-9-1-alpha">
  <title>Release 9.1alpha1</title>
  <sect2>
    <title>Overview</title>
    <para>
      PostgreSQL alpha releases are snapshots of development code. They
      are intended to preview and test upcoming features and to provide
      the possibility for early feedback. They should not be used in
      production installations or active development projects. While the
      PostgreSQL code is continuously subject to a number of automated
      and manual tests, alpha releases might have serious bugs. Also
      features may be changed incompatibly or removed at any time during
      the development cycle.
    </para>
    <para>
      The development cycle of a PostgreSQL major release alternates
      between periods of development and periods of integration work,
      called commit fests, normally one month each. Alpha releases are
      planned to be produced at the end of every commit fest, thus every
      two months. Since the first commit fest starts within a month from
      the beginning of development altogether, early alpha releases are
      not indicative of the likely feature set of the final release.
    </para>
    <para>
      The release notes below highlight user visible changes and new
      features. There are normally numerous bug fixes and performance
      improvements in every new snapshot of PostgreSQL, and it would be
      too bulky to attempt to list them all. Note that many bug fixes are
      also backported to stable releases of PostgreSQL, and you should be
      using those if you are looking for bug-fix-only upgrades for your
      current installations.
    </para>
    <para>
      These notes are cumulative over all alpha releases of the current
      development cycle.  Items that are new in the latest alpha release are
      <emphasis>emphasized</emphasis>.
    </para>
  </sect2>
  <sect2>
    <title>Migration</title>
    <para>
      To upgrade from any release to an alpha release or from an alpha
      release to any other release will most likely require a
      dump/restore upgrade procedure. It may happen that this is not
      necessary in particular cases, but that is not verified beforehand.
      (The server will warn you in any case when a dump/restore is
      necessary if you attempt to use it with an old data directory.)
      Note, however, that the dump/restore upgrade procedure is expected
      to work for alpha releases, and problems in this area should be
      reported.
    </para>
  </sect2>
  <sect2>
    <title>Testing</title>
    <para>
      The primary reason we release alphas is to get users to test new
      features as early as possible.  If you are interested in helping
      with organized testing, please see
      <ulink url="http://wiki.postgresql.org/wiki/HowToBetaTest">the
      testing information page</ulink>.
      </para>
  </sect2>
  <sect2>
    <title>Changes</title>
    <sect3>
      <title>SQL Features</title>
      <itemizedlist>

       <listitem>
        <para>
         <emphasis>Recognize functional dependency on primary
         keys</emphasis>
        </para>
        <para>
         This allows a table's other columns to be referenced without listing
         them in GROUP BY, so long as the primary key column(s) are listed in
         GROUP BY.
        </para>
       </listitem>

       <listitem>
        <para>
         <emphasis>Add CREATE TABLE IF NOT EXISTS</emphasis>
        </para>
       </listitem>

      </itemizedlist>
    </sect3>
    <sect3>
      <title>Performance</title>
      <itemizedlist>

       <listitem>
        <para>
         <emphasis>Reduce lock levels of CREATE TRIGGER and some ALTER
         TABLE, CREATE RULE actions</emphasis>
        </para>
       </listitem>

       <listitem>
        <para>
         <emphasis>Add some knowledge about prefix matches to
         tsmatchsel()</emphasis>
        </para>
       </listitem>

       <listitem>
        <para>
         <emphasis>Replace the naive HYPOT() macro with a
         standards-conformant hypotenuse function</emphasis>
        </para>
       </listitem>

      </itemizedlist>
    </sect3>
    <sect3>
      <title>Server Settings</title>
      <itemizedlist>

       <listitem>
        <para>
         <emphasis>Change the default value of
         <literal>standard_conforming_strings</> to
         <literal>on</></emphasis>
        </para>
        <warning>
         <para>
          This is a significant incompatibility with previous releases,
          because it may break unwary applications in security-critical ways.
         </para>
        </warning>
       </listitem>

       <listitem>
        <para>
         <emphasis>Add <literal>log_file_mode</> parameter</emphasis>
        </para>
        <para>
         This allows control of the file permissions set on log files created
         by the syslogger process.
        </para>
       </listitem>

       <listitem>
        <para>
         <emphasis>Add <literal>restart_after_crash</> parameter</emphasis>
        </para>
        <para>
         Normally, we automatically restart after a backend crash, but in
         some cases when PostgreSQL is invoked by clusterware it may be
         desirable to suppress this behavior, so we now provide an option which
         does that.
        </para>
       </listitem>

      </itemizedlist>
    </sect3>
    <sect3>
      <title>Administration and Monitoring</title>
      <itemizedlist>

       <listitem>
        <para>
         <emphasis>Make EXPLAIN show the function call expression of a
         FunctionScan plan node, but only in VERBOSE mode</emphasis>
        </para>
       </listitem>

       <listitem>
        <para>
         <emphasis>Make EXPLAIN print PARAM_EXEC Params as
         the referenced expressions, rather than just $N</emphasis>
        </para>
       </listitem>

       <listitem>
        <para>
         <emphasis>Add vacuum and analyze counters to pg_stat_*_tables
         views</emphasis>
        </para>
       </listitem>

       <listitem>
        <para>
         <emphasis>Add stats functions and views to provide access to a
         transaction's own statistics counts</emphasis>
        </para>
       </listitem>

      </itemizedlist>
    </sect3>
    <sect3>
      <title>Security</title>
      <itemizedlist>

       <listitem>
        <para>
         <emphasis>Add server authentication over Unix-domain
         sockets</emphasis>
        </para>
        <para>
         This adds a libpq connection parameter <literal>requirepeer</> that
         specifies the user name that the server process is expected to run
         under.
        </para>
       </listitem>

      </itemizedlist>
    </sect3>
    <sect3>
      <title>Built-In Functions</title>
      <itemizedlist>

       <listitem>
        <para>
         <emphasis>Add string functions: concat(), concat_ws(), left(),
         right(), and reverse()</emphasis>
        </para>
       </listitem>

       <listitem>
        <para>
         <emphasis>Add three-parameter forms of array_to_string and
         string_to_array</emphasis>
        </para>
       </listitem>

       <listitem>
        <para>
         <emphasis>Add XMLEXISTS function</emphasis>
        </para>
       </listitem>

       <listitem>
        <para>
         <emphasis>Add xpath_exists() function</emphasis>
        </para>
        <para>
         This is equivalent to XMLEXISTS except that it offers support for
         namespace mapping.
        </para>
       </listitem>

       <listitem>
        <para>
         <emphasis>Add xml_is_well_formed, xml_is_well_formed_document,
         xml_is_well_formed_content functions to the core XML
         code</emphasis>
        </para>
        <para>
         These supersede a version previously offered by contrib/xml2.
        </para>
       </listitem>

      </itemizedlist>
    </sect3>
    <sect3>
      <title>Data Types</title>
      <itemizedlist>

       <listitem>
        <para>
         <emphasis>Allow numeric to use a more compact, 2-byte header in
         many cases</emphasis>
        </para>
       </listitem>

       <listitem>
        <para>
         <emphasis>Add support for dividing money by money (yielding a
         float8 result) and for casting between money and numeric</emphasis>
        </para>
       </listitem>

      </itemizedlist>
    </sect3>
    <sect3>
      <title>Server Tools</title>
      <itemizedlist>

       <listitem>
        <para>
         <emphasis>Add options to force quoting of all
         identifiers</emphasis>
        </para>
        <para>
         This includes a quote_all_identifiers parameter which affects the
         behavior of the backend, and a --quote-all-identifiers argument to
         pg_dump and pg_dumpall which sets the parameter and also affects the
         quoting done internally by those applications.
        </para>
       </listitem>

      </itemizedlist>
    </sect3>
    <sect3>
      <title>psql</title>
      <itemizedlist>

       <listitem>
        <para>
         <emphasis>Add \conninfo command to psql, to show current connection
         info</emphasis>
        </para>
       </listitem>

       <listitem>
        <para>
         <emphasis>Extend psql's \e and \ef commands so that a line number
         can be specified, and the editor's cursor will be initially placed
         on that line</emphasis>
        </para>
        <para>
         To avoid assumptions about what switch the user's editor takes for
         this purpose, there is a new psql variable EDITOR_LINENUMBER_SWITCH
         with (at present) no default value.
        </para>
       </listitem>

       <listitem>
        <para>
         <emphasis>Add a \sf (show function) command to psql, for those
         times when you need to look at a function but don't wish to fire up
         an editor</emphasis>
        </para>
       </listitem>

       <listitem>
        <para>
         <emphasis>Make psql distinguish between unique indices and unique
         constraints in \d printout</emphasis>
        </para>
       </listitem>

      </itemizedlist>
    </sect3>
    <sect3>
      <title>Procedural Languages</title>
      <sect4>
       <title>PL/pgSQL</title>
      <itemizedlist>

       <listitem>
        <para>
         <emphasis>Modify the handling of RAISE without parameters so that
         the error it throws can be caught in the same places that could
         catch an ordinary RAISE ERROR in the same location</emphasis>
        </para>
        <para>
         The previous coding insisted on throwing the error from the block
         containing the active exception handler; which is arguably more
         surprising, and definitely unlike Oracle's behavior.
        </para>
       </listitem>

       <listitem>
        <para>
         <emphasis>Remove ancient PL/pgSQL line numbering hack</emphasis>
        </para>
        <para>
         PL/pgSQL used to count the second line of the function body as
         <quote>line 1</>, if the first line was zero-length.
         While this hack arguably has some benefit in terms of making
         PL/pgsql's line numbering match the programmer's expectations, it
         also makes PL/pgsql inconsistent with the remaining PLs, making it
         difficult for clients to reliably determine where the error
         actually is.  On balance, it seems better to be consistent.
        </para>
       </listitem>

      </itemizedlist>
      </sect4>
    </sect3>
    <sect3>
      <title>Additional Supplied Modules</title>
      <itemizedlist>

       <listitem>
        <para>
         <emphasis>Add the ability to compute per-statement latencies (ie,
         average execution times) to pgbench</emphasis>
        </para>
       </listitem>

       <listitem>
        <para>
         <emphasis>Teach levenshtein() about multi-byte
         characters</emphasis>
        </para>
       </listitem>

       <listitem>
        <para>
         <emphasis>Add btree_gist support for searching on <quote>not
         equals</quote></emphasis>
        </para>
       </listitem>

       <listitem>
        <para>
         <emphasis>Add ssl_cipher() and ssl_version() functions to
         contrib/sslinfo</emphasis>
        </para>
       </listitem>

       <listitem>
        <para>
         <emphasis>Remove the arbitrary (and undocumented) limit on the
         number of parameter=value pairs that can be handled by
         xslt_process()</emphasis>
        </para>
       </listitem>

      </itemizedlist>
    </sect3>
    <sect3>
      <title>Source Code, Build Options</title>
      <itemizedlist>

       <listitem>
        <para>
         <emphasis>Include the backend ID in the relpath of temporary
         relations</emphasis>
        </para>
        <para>
         This allows us to reliably remove all leftover temporary relation
         files on cluster startup without reference to system catalogs or
         WAL; therefore, we no longer include temporary relations in
         XLOG_XACT_COMMIT and XLOG_XACT_ABORT WAL records.
        </para>
       </listitem>

       <listitem>
        <para>
         <emphasis>Rewrite COMMENT ON <replaceable>object</> code for better
         modularity, and add necessary locking</emphasis>
        </para>
       </listitem>

       <listitem>
        <para>
         <emphasis>Add a hook in ExecCheckRTPerms() for eventual use by
         external security-checking modules</emphasis>
        </para>
       </listitem>

       <listitem>
        <para>
         <emphasis>Standardize names and calling conventions of
         get_whatever_oid functions</emphasis>
        </para>
       </listitem>

       <listitem>
        <para>
         <emphasis>Make NestLoop plan nodes pass outer-relation variables
         into their inner relation using the general PARAM_EXEC executor
         parameter mechanism, rather than the ad-hoc kluge of passing the
         outer tuple down through ExecReScan</emphasis>
        </para>
       </listitem>

       <listitem>
        <para>
         <emphasis>Make details of the Numeric representation private to
         numeric.c</emphasis>
        </para>
       </listitem>

       <listitem>
        <para>
         <emphasis>Suppress some compiler warnings from
         <literal>clang</></emphasis>
        </para>
       </listitem>

      </itemizedlist>
    </sect3>
  </sect2>
</sect1>
