regress.sgml

PostgreSQL7.4.6 for Linux

     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.  However, your operating system must provide
     support for the <literal>PST8PDT</literal> time zone, or the time zone-dependent
     tests will fail. To verify that your machine does have this
     support, type the following:
<screen>
env TZ=PST8PDT date
</screen>
     The command above should have returned the current system time in
     the <literal>PST8PDT</literal> time zone. If the <literal>PST8PDT</literal> time zone is not available,
     then your system may have returned the time in UTC. If the
     <literal>PST8PDT</literal> time zone is missing, you can set the time zone
     rules explicitly:
<programlisting>
PGTZ='PST8PDT7,M04.01.0,M10.05.03'; export PGTZ
</programlisting>
    </para>

    <para>
     There appear to be some systems that do not accept the
     recommended syntax for explicitly setting the local time zone
     rules; you may need to use a different <envar>PGTZ</envar>
     setting on such machines.
    </para>

    <para>
     Some systems using older time-zone libraries fail to apply
     daylight-saving corrections to dates before 1970, causing
     pre-1970 <acronym>PDT</acronym> times to be displayed in <acronym>PST</acronym> instead.  This will
     result in localized differences in the test 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>
     There is at least one case in the <literal>random</literal> test
     script that is intended to produce random results. This causes
     random to fail the regression test once in a while (perhaps once
     in every five to ten trials).  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 always fails in repeated
     attempts.  (On the other hand, if the random test is
     <emphasis>never</emphasis> reported to fail even in many trials
     of the regression tests, you probably <emphasis>should</emphasis>
     worry.)
    </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 using older time zone libraries fail to apply
    daylight-saving corrections to dates before 1970, causing
    pre-1970 <acronym>PDT</acronym> times to be displayed in <acronym>PST</acronym> instead.  This causes a
    few differences in the <filename>horology</> regression test.
    Therefore, we provide a variant comparison file,
    <filename>horology-no-DST-before-1970.out</filename>, which includes
    the results to be expected on these systems.  To silence the bogus
    <quote>failure</quote> message on <systemitem>HPUX</systemitem> platforms,
    <filename>resultmap</filename> includes
<programlisting>
horology/.*-hpux=horology-no-DST-before-1970
</programlisting>
    which will trigger on any machine for which the output of
    <command>config.guess</command> includes <literal>-hpux</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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