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

  <abstract>
   <para>
    Regression test instructions and analysis
   </para>
  </abstract>

  <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>.  The test suite was
   originally developed by Jolly Chen and Andrew Yu, and was
   extensively revised and repackaged by Marc Fournier and Thomas
   Lockhart.  From <productname>PostgreSQL</productname> 6.1 onward
   the regression tests are current for every official release.
  </para>

  <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>
<prompt>$ </prompt><userinput>gmake check</userinput>
</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
   platform-dependent <quote>expected</quote> files and some sample
   user-defined trigger functions, and then run the test driver
   script.  At the end you should see something like
<screen>
<computeroutput>
======================
 All 77 tests passed.
======================
</computeroutput>
</screen>
   or otherwise a note about what tests failed.  See <xref
   linkend="regress-evaluation"> below for more.
  </para>

  <note>
   <para>
    Because this test method runs a temporary server, it will not work
    when you are the root user (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>su - joeuser</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>
  </note>

  <tip>
   <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:
    <informalexample>
<screen>
<prompt>$ </prompt><userinput>gmake SHELL=/bin/ksh check</userinput>
</screen>
    </informalexample>
   </para>
  </tip>

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

  <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
    <application>diff</application> 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 <application>diff</application> 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 <application>diff</application> 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>
     The tests expect to run in plain <quote>C</quote> locale.  This
     should not cause any problems when you run the tests against a
     temporary installation, since the regression test driver takes care
     to start the server in C locale.  However, if you run the tests
     against an already-installed server that is using non-C locale settings,
     you may see differences caused by varying rules for string sort order,
     formatting of numeric and monetary values, and so forth.
    </para>

    <para>
     In some locales the resulting differences are small and easily checked by
     inspection.  However, in a locale that changes the rules for formatting
     of numeric values (typically by swapping the usage of commas and
     decimal points), entry of some data values will fail, resulting in
     extensive differences later in the tests where the missing data values
     are supposed to be used.
    </para>
   </sect2>
    
   <sect2>
    <title>Date and time differences</title>

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

    <para>
     Most of the date and time results are dependent on the time zone
     environment.  The reference files are generated for time zone
     PST8PDT (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 system must provide library
     support for the PST8PDT time zone, or the time zone-dependent
     tests will fail. To verify that your machine does have this
     support, type the following:
<screen>
<prompt>$ </prompt><userinput>env TZ=PST8PDT date</userinput>
</screen>
     The command above should have returned the current system time in
     the PST8PDT time zone. If the PST8PDT database is not available,
     then your system may have returned the time in GMT. If the
     PST8PDT time zone is not available, 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-savings corrections to dates before 1970, causing
     pre-1970 PDT times to be displayed in PST 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 (<type>double
     precision</type>) numbers from table columns. Differences in
     results involving mathematical functions of <type>double
     precision</type> columns have been observed.  The float8 and
     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 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>Polygon differences</title>
      
    <para>
     Several of the tests involve operations on geographic data about
     the Oakland/Berkeley, CA street map. The map data is expressed as
     polygons whose vertices are represented as pairs of <type>double
     precision</type> numbers (decimal latitude and
     longitude). Initially, some tables are created and loaded with
     geographic data, then some views are created that join two
     tables using the polygon intersection operator
     (<literal>##</literal>), then a select is done on the view.
    </para>

    <para>
     When comparing the results from different platforms, differences
     occur in the 2nd or 3rd place to the right of the decimal
     point. The SQL statements where these problems occur are the
     following:
<programlisting>
SELECT * from street;
SELECT * from iexit;
</programlisting>
    </para>
   </sect2>

   <sect2>
    <title>Tuple ordering differences</title>
      
    <para>
You might see differences in which the same tuples 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 ORDER BY for every single
SELECT, and so their result tuple orderings are not well-defined
according to the letter of the SQL spec.  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 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 ORDER BY that your result
is violating.  But please report it anyway, so that we can add an
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 regress test SELECTs 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 <quote>random</quote> 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 regress 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>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
    expr(1) (that is, a regular expression with an implicit
    <literal>^</literal> anchor
    at the start).  It is matched against the platform name as printed
    by <filename>config.guess</filename> 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-savings corrections to dates before 1970, causing
    pre-1970 PDT times to be displayed in PST 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 HPPA platforms, resultmap
    includes
<programlisting>
horology/hppa=horology-no-DST-before-1970
</programlisting>
    which will trigger on any machine for which config.guess's output
    begins with <quote><literal>hppa</literal></quote>.  Other lines
    in resultmap select the variant comparison file for other
    platforms where it's appropriate.
   </para>
    
  </sect1>
  
</chapter>

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