32.2. Test Evaluation
Some properly installed and fully functional
PostgreSQL
installations can
"
fail
"
some of these regression tests due to
platform-specific artifacts such as varying floating-point representation
and message wording. The tests are currently evaluated using a simple
diff
comparison against the outputs
generated on a reference system, so the results are sensitive to
small system differences. When a test is reported as
"
failed
"
, always examine the differences between
expected and actual results; you might 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.
The actual outputs of the regression tests are in files in the
src/test/regress/results
directory. The test
script uses
diff
to compare each output
file against the reference outputs stored in the
src/test/regress/expected
directory. Any
differences are saved for your inspection in
src/test/regress/regression.diffs
.
(When running a test suite other than the core tests, these files
of course appear in the relevant subdirectory,
not
src/test/regress
.)
If you don't
like the
diff
options that are used by default, set the
environment variable
PG_REGRESS_DIFF_OPTS
, for
instance
PG_REGRESS_DIFF_OPTS='-c'
. (Or you
can run
diff
yourself, if you prefer.)
If for some reason a particular platform generates a " failure " for a given test, but inspection of the output convinces you that the result is valid, you can add a new comparison file to silence the failure report in future test runs. See Section 32.3 for details.
32.2.1. Error Message Differences
Some of the regression tests involve intentional invalid input values. Error messages can come from either the PostgreSQL code or from the host platform system routines. In the latter case, the messages can vary between platforms, but should reflect similar information. These differences in messages will result in a " failed " regression test that can be validated by inspection.
32.2.2. Locale Differences
If you run the tests against a server that was initialized with a collation-order locale other than C, then there might be differences due to sort order and subsequent failures. The regression test suite is set up to handle this problem by providing alternate result files that together are known to handle a large number of locales.
To run the tests in a different locale when using the
temporary-installation method, pass the appropriate
locale-related environment variables on
the
make
command line, for example:
make check LANG=de_DE.utf8
(The regression test driver unsets
LC_ALL
, so it
does not work to choose the locale using that variable.) To use
no locale, either unset all locale-related environment variables
(or set them to
C
) or use the following
special invocation:
make check NO_LOCALE=1
When running the tests against an existing installation, the
locale setup is determined by the existing installation. To
change it, initialize the database cluster with a different
locale by passing the appropriate options
to
initdb
.
In general, it is advisable to try to run the regression tests in the locale setup that is wanted for production use, as this will exercise the locale- and encoding-related code portions that will actually be used in production. Depending on the operating system environment, you might get failures, but then you will at least know what locale-specific behaviors to expect when running real applications.
32.2.3. Date and Time Differences
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
PGTZ
to
PST8PDT
, which normally
ensures proper results.
32.2.4. Floating-Point Differences
Some of the tests involve computing 64-bit floating-point numbers (
double
precision
) from table columns. Differences in
results involving mathematical functions of
double
precision
columns have been observed. The
float8
and
geometry
tests are particularly prone to small differences
across platforms, or even with different compiler optimization settings.
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.
Some systems display minus zero as
-0
, while others
just show
0
.
Some systems signal errors from
pow()
and
exp()
differently from the mechanism
expected by the current
PostgreSQL
code.
32.2.5. Row Ordering Differences
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
ORDER BY
for every single
SELECT
, and so their result row orderings are not well-defined
according to 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,
so the lack of
ORDER BY
is not a problem. Some queries do exhibit
cross-platform ordering differences, however. When testing against an
already-installed server, ordering differences can also be caused by
non-C locale settings or non-default parameter settings, such as custom values
of
work_mem
or the planner cost parameters.
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. However, please report it anyway, so that we can add an
ORDER BY
to that particular query to eliminate the bogus
"
failure
"
in future releases.
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.
32.2.6. Insufficient Stack Depth
If the
errors
test results in a server crash
at the
select infinite_recurse()
command, it means that
the platform's limit on process stack size is smaller than the
max_stack_depth
parameter indicates. This
can be fixed by running the server under a higher stack
size limit (4MB is recommended with the default value of
max_stack_depth
). If you are unable to do that, an
alternative is to reduce the value of
max_stack_depth
.
On platforms supporting
getrlimit()
, the server should
automatically choose a safe value of
max_stack_depth
;
so unless you've manually overridden this setting, a failure of this
kind is a reportable bug.
32.2.7. The " random " Test
The
random
test script is intended to produce
random results. In very rare cases, this causes that regression
test to fail. Typing:
diff results/random.out expected/random.out
should produce only one or a few lines of differences. You need not worry unless the random test fails repeatedly.
32.2.8. Configuration Parameters
When running the tests against an existing installation, some non-default
parameter settings could cause the tests to fail. For example, changing
parameters such as
enable_seqscan
or
enable_indexscan
could cause plan changes that would
affect the results of tests that use
EXPLAIN
.