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 <chapter id="regress">
  <title id="regress-title">Regression Tests</title>

  <indexterm zone="regress">
   <primary>regression tests</primary>
  </indexterm>

  <indexterm zone="regress">
   <primary>test</primary>
  </indexterm>

  <para>
   The regression tests are a comprehensive set of tests for the SQL
   implementation in <productname>PostgreSQL</productname>.  They test
   standard SQL operations as well as the extended capabilities of
   <productname>PostgreSQL</productname>.  From
   <productname>PostgreSQL</productname> 6.1 onward, the regression
   tests are current for every official release.
  </para>

  <sect1 id="regress-run">
   <title>Running the Tests</title>

  <para>
   The regression test can be run against an already installed and
   running server, or using a temporary installation within the build
   tree.  Furthermore, there is a <quote>parallel</quote> and a
   <quote>sequential</quote> mode for running the tests.  The
   sequential method runs each test script in turn, whereas the
   parallel method starts up multiple server processes to run groups
   of tests in parallel.  Parallel testing gives confidence that
   interprocess communication and locking are working correctly.  For
   historical reasons, the sequential test is usually run against an
   existing installation and the parallel method against a temporary
   installation, but there are no technical reasons for this.
  </para>

  <para>
   To run the regression tests after building but before installation,
   type
<screen>
gmake check
</screen>
   in the top-level directory.  (Or you can change to
   <filename>src/test/regress</filename> and run the command there.)
   This will first build several auxiliary files, such as
   some sample
   user-defined trigger functions, and then run the test driver
   script.  At the end you should see something like
<screen>
<computeroutput>
======================
 All 93 tests passed.
======================
</computeroutput>
</screen>
   or otherwise a note about which tests failed.  See <xref
   linkend="regress-evaluation"> below for more.
  </para>

   <para>
    Because this test method runs a temporary server, it will not work
    when you are the root user (since the server will not start as root).
    If you already did the build as root, you do not have to start all
    over.  Instead, make the regression test directory writable by
    some other user, log in as that user, and restart the tests.
    For example
<screen>
<prompt>root# </prompt><userinput>chmod -R a+w src/test/regress</userinput>
<prompt>root# </prompt><userinput>chmod -R a+w contrib/spi</userinput>
<prompt>root# </prompt><userinput>su - joeuser</userinput>
<prompt>joeuser$ </prompt><userinput>cd <replaceable>top-level build directory</></userinput>
<prompt>joeuser$ </prompt><userinput>gmake check</userinput>
</screen>
    (The only possible <quote>security risk</quote> here is that other
    users might be able to alter the regression test results behind
    your back.  Use common sense when managing user permissions.)
   </para>
   <para>
    Alternatively, run the tests after installation.
   </para>

   <para>
    The parallel regression test starts quite a few processes under your
    user ID.  Presently, the maximum concurrency is twenty parallel test
    scripts, which means sixty processes: there's a server process, a
    <application>psql</>, and usually a shell parent process for the
    <application>psql</> for each test script.
    So if your system enforces a per-user limit on the number of processes,
    make sure this limit is at least seventy-five or so, else you may get
    random-seeming failures in the parallel test.  If you are not in
    a position to raise the limit, you can cut down the degree of parallelism
    by setting the <literal>MAX_CONNECTIONS</> parameter.  For example,
<screen>
gmake MAX_CONNECTIONS=10 check
</screen>
    runs no more than ten tests concurrently.
   </para>

   <para>
    On some systems, the default Bourne-compatible shell
    (<filename>/bin/sh</filename>) gets confused when it has to manage
    too many child processes in parallel.  This may cause the parallel
    test run to lock up or fail.  In such cases, specify a different
    Bourne-compatible shell on the command line, for example:
<screen>
gmake SHELL=/bin/ksh check
</screen>
    If no non-broken shell is available, you may be able to work around the
    problem by limiting the number of connections, as shown above.
   </para>

  <para>
   To run the tests after installation<![%standalone-ignore;[ (see <xref linkend="installation">)]]>,
   initialize a data area and start the
   server, <![%standalone-ignore;[as explained in <xref linkend="runtime">, ]]> then type
<screen>
gmake installcheck
</screen>
   The tests will expect to contact the server at the local host and the
   default port number, unless directed otherwise by <envar>PGHOST</envar> and <envar>PGPORT</envar>
   environment variables.
  </para>
  </sect1>

  <sect1 id="regress-evaluation">
   <title>Test Evaluation</title> 

   <para>
    Some properly installed and fully functional
    <productname>PostgreSQL</productname> installations can
    <quote>fail</quote> some of these regression tests due to
    platform-specific artifacts such as varying floating-point representation
    and time zone support. The tests are currently evaluated using a simple
    <command>diff</command> comparison against the outputs
    generated on a reference system, so the results are sensitive to
    small system differences.  When a test is reported as
    <quote>failed</quote>, always examine the differences between
    expected and actual results; you may well find that the
    differences are not significant.  Nonetheless, we still strive to
    maintain accurate reference files across all supported platforms,
    so it can be expected that all tests pass.
   </para>

   <para>
    The actual outputs of the regression tests are in files in the
    <filename>src/test/regress/results</filename> directory. The test
    script uses <command>diff</command> to compare each output
    file against the reference outputs stored in the
    <filename>src/test/regress/expected</filename> directory.  Any
    differences are saved for your inspection in
    <filename>src/test/regress/regression.diffs</filename>.  (Or you
    can run <command>diff</command> yourself, if you prefer.)
   </para>

   <sect2>
    <title>Error message differences</title>
      
    <para>
     Some of the regression tests involve intentional invalid input
     values.  Error messages can come from either the
     <productname>PostgreSQL</productname> code or from the host
     platform system routines. In the latter case, the messages may
     vary between platforms, but should reflect similar
     information. These differences in messages will result in a
     <quote>failed</quote> regression test that can be validated by
     inspection.
    </para>
   </sect2>
    
   <sect2>
    <title>Locale differences</title>

    <para>
     If you run the tests against an already-installed server that was
     initialized with a collation-order locale other than C, then
     there may be differences due to sort order and follow-up
     failures.  The regression test suite is set up to handle this
     problem by providing alternative result files that together are
     known to handle a large number of locales.  For example, for the
     <literal>char</literal> test, the expected file
     <filename>char.out</filename> handles the <literal>C</> and <literal>POSIX</> locales,
     and the file <filename>char_1.out</filename> handles many other
     locales.  The regression test driver will automatically pick the
     best file to match against when checking for success and for
     computing failure differences.  (This means that the regression
     tests cannot detect whether the results are appropriate for the
     configured locale.  The tests will simply pick the one result
     file that works best.)
    </para>

    <para>
     If for some reason the existing expected files do not cover some
     locale, you can add a new file.  The naming scheme is
     <literal><replaceable>testname</>_<replaceable>digit</>.out</>.
     The actual digit is not significant.  Remember that the
     regression test driver will consider all such files to be equally
     valid test results.  If the test results are platform-specific,
     the technique described in <xref linkend="regress-platform">
     should be used instead.
    </para>
   </sect2>
    
   <sect2>
    <title>Date and time differences</title>

    <para>
     A few of the queries in the <filename>horology</filename> test will
     fail if you run the test on the day of a daylight-saving time
     changeover, or the day after one.  These queries expect that
     the intervals between midnight yesterday, midnight today and
     midnight tomorrow are exactly twenty-four hours --- which is wrong
     if daylight-saving time went into or out of effect meanwhile.
    </para>

    <note>
     <para>
      Because USA daylight-saving time rules are used, this problem always
      occurs on the first Sunday of April, the last Sunday of October,
      and their following Mondays, regardless of when daylight-saving time
      is in effect where you live.  Also note that the problem appears or
      disappears at midnight Pacific time (UTC-7 or UTC-8), not midnight
      your local time.  Thus the failure may appear late on Saturday or
      persist through much of Tuesday, depending on where you live.
     </para>
    </note>

    <para>
     Most of the date and time results are dependent on the time zone
     environment.  The reference files are generated for time zone
     <literal>PST8PDT</literal> (Berkeley, California), and there will be
     apparent failures if the tests are not run with that time zone setting.
     The regression test driver sets environment variable
     <envar>PGTZ</envar> to <literal>PST8PDT</literal>, which normally
     ensures proper results.
    </para>
   </sect2>
    
   <sect2>
    <title>Floating-point differences</title>
      
    <para>
     Some of the tests involve computing 64-bit floating-point numbers (<type>double
     precision</type>) from table columns. Differences in
     results involving mathematical functions of <type>double
     precision</type> columns have been observed.  The <literal>float8</> and
     <literal>geometry</> tests are particularly prone to small differences
     across platforms, or even with different compiler optimization options.
     Human eyeball comparison is needed to determine the real
     significance of these differences which are usually 10 places to
     the right of the decimal point.
    </para>

    <para>
     Some systems display minus zero as <literal>-0</>, while others
     just show <literal>0</>.
    </para>

    <para>
     Some systems signal errors from <function>pow()</function> and
     <function>exp()</function> differently from the mechanism
     expected by the current <productname>PostgreSQL</productname>
     code.
    </para>
   </sect2>

   <sect2>
    <title>Row ordering differences</title>
      
    <para>
You might see differences in which the same rows are output in a
different order than what appears in the expected file.  In most cases
this is not, strictly speaking, a bug.  Most of the regression test
scripts are not so pedantic as to use an <literal>ORDER BY</> for every single
<literal>SELECT</>, and so their result row orderings are not well-defined
according to the letter of the SQL specification.  In practice, since we are
looking at the same queries being executed on the same data by the same
software, we usually get the same result ordering on all platforms, and
so the lack of <literal>ORDER BY</> isn't a problem.  Some queries do exhibit
cross-platform ordering differences, however.  (Ordering differences
can also be triggered by non-C locale settings.)
    </para>

    <para>
Therefore, if you see an ordering difference, it's not something to
worry about, unless the query does have an <literal>ORDER BY</> that your result
is violating.  But please report it anyway, so that we can add an
<literal>ORDER BY</> to that particular query and thereby eliminate the bogus
<quote>failure</quote> in future releases.
    </para>

    <para>
You might wonder why we don't order all the regression test queries explicitly to
get rid of this issue once and for all.  The reason is that that would
make the regression tests less useful, not more, since they'd tend
to exercise query plan types that produce ordered results to the
exclusion of those that don't.
    </para>
   </sect2>

   <sect2>
    <title>The <quote>random</quote> test</title>
      
    <para>
     The <literal>random</literal> test script is intended to produce 
     random results.   In rare cases, this causes the random regression
     test to fail.  Typing
<programlisting>
diff results/random.out expected/random.out
</programlisting>
     should produce only one or a few lines of differences.  You need
     not worry unless the random test repeatedly fails.
    </para>
   </sect2>
  </sect1>

<!-- We might want to move the following section into the developer's guide. -->
  <sect1 id="regress-platform">
   <title>Platform-specific comparison files</title>

   <para>
    Since some of the tests inherently produce platform-specific
    results, we have provided a way to supply platform-specific result
    comparison files.  Frequently, the same variation applies to
    multiple platforms; rather than supplying a separate comparison
    file for every platform, there is a mapping file that defines
    which comparison file to use.  So, to eliminate bogus test
    <quote>failures</quote> for a particular platform, you must choose
    or make a variant result file, and then add a line to the mapping
    file, which is <filename>src/test/regress/resultmap</filename>.
   </para>

   <para>
    Each line in the mapping file is of the form
<synopsis>
testname/platformpattern=comparisonfilename
</synopsis>
    The test name is just the name of the particular regression test
    module.  The platform pattern is a pattern in the style of the Unix
    tool <command>expr</> (that is, a regular expression with an implicit
    <literal>^</literal> anchor
    at the start).  It is matched against the platform name as printed
    by <command>config.guess</command> followed by
    <literal>:gcc</literal> or <literal>:cc</literal>, depending on
    whether you use the GNU compiler or the system's native compiler
    (on systems where there is a difference).  The comparison file
    name is the name of the substitute result comparison file.
   </para>

   <para>
    For example: some systems interpret very small floating-point values
    as zero, rather than reporting an underflow error.  This causes a
    few differences in the <filename>float8</> regression test.
    Therefore, we provide a variant comparison file,
    <filename>float8-small-is-zero.out</filename>, which includes
    the results to be expected on these systems.  To silence the bogus
    <quote>failure</quote> message on <systemitem>OpenBSD</systemitem>
    platforms, <filename>resultmap</filename> includes
<programlisting>
float8/i.86-.*-openbsd=float8-small-is-zero
</programlisting>
    which will trigger on any machine for which the output of
    <command>config.guess</command> matches <literal>i.86-.*-openbsd</literal>.
    Other lines
    in <filename>resultmap</> select the variant comparison file for other
    platforms where it's appropriate.
   </para>
    
  </sect1>
  
</chapter>

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