Thread

1. Environment variable to disable diffs file output

   Ilya Cherdakov <i.cherdakov.pg@gmail.com> — 2026-04-06T07:55:25Z

   Greetings!
   
   I'd like to add a environment variable to the patch to
   disable diff output. Sometimes you have to be creative
   with exploratory testing, modifying test files, etc.,
   and multiple diff outputs can become a nuisance. This
   doesn't change the default behavior, but it does give
   you control over diff output in tests for specific
   scenarios where a large number of failures are expected
   (mass runs or exploratory testing with changing tests).
   
   The env usage and implementation are somewhat similar
   to PG_REGRESS_DIFF_OPTS
        PG_REGRESS_DISABLE_DIFFS_OUTPUT=1 make check -s.
   
   For now, I suggest to simply disabling it, but I'm also
   considering passing the number of lines to output via env
   or via flag pg_regress instead of completely disabling it.
   Something like
        PG_REGRESS_DIFFS_NUMBER_LINES_OUTPUT=20 make check
   and then when an error occurs, 20 lines will be output
   instead of the default 80. Setting it to 0 disables
   diffs output.
   
   
   I think this small addition will be useful for many
   developers, especially testers.
   ---
   This is my first patch. I welcome critique and comments.
   Best regards,
   Ilya Cherdakov, PostgresPro

2. Re: Environment variable to disable diffs file output

   Jelte Fennema-Nio <postgres@jeltef.nl> — 2026-04-06T09:47:02Z

   On Mon, 6 Apr 2026 at 09:56, Илья Чердаков <i.cherdakov.pg@gmail.com> wrote:
   > I'd like to add a environment variable to the patch to
   > disable diff output. Sometimes you have to be creative
   > with exploratory testing, modifying test files, etc.,
   > and multiple diff outputs can become a nuisance. This
   > doesn't change the default behavior, but it does give
   > you control over diff output in tests for specific
   > scenarios where a large number of failures are expected
   > (mass runs or exploratory testing with changing tests).
   
   I'm fine with adding the abilitity to configure what pg_regress should
   print, but it's unclear to me what's special about the diff output
   compared to all the other output? i.e. what is the output you would
   actually like to see for your use case? Piping everything to /dev/null
   would silence all output except for the exit code, but I guess you
   want some output. i.e. what do you do with the output that you get? Do
   you only want to know which tests failed? If so, do you care about
   which tests are passing?
   
   
   
   

3. Re: Environment variable to disable diffs file output

   Daniel Gustafsson <daniel@yesql.se> — 2026-04-06T14:11:02Z

   > On 6 Apr 2026, at 09:55, Илья Чердаков <i.cherdakov.pg@gmail.com> wrote:
   
   > I'd like to add a environment variable to the patch to
   > disable diff output. Sometimes you have to be creative
   > with exploratory testing, modifying test files, etc.,
   > and multiple diff outputs can become a nuisance. This
   > doesn't change the default behavior, but it does give
   > you control over diff output in tests for specific
   > scenarios where a large number of failures are expected
   > (mass runs or exploratory testing with changing tests).
   > 
   > The env usage and implementation are somewhat similar
   > to PG_REGRESS_DIFF_OPTS
   >     PG_REGRESS_DISABLE_DIFFS_OUTPUT=1 make check -s.
   > 
   > For now, I suggest to simply disabling it, but I'm also
   > considering passing the number of lines to output via env
   > or via flag pg_regress instead of completely disabling it.
   > Something like
   >     PG_REGRESS_DIFFS_NUMBER_LINES_OUTPUT=20 make check
   > and then when an error occurs, 20 lines will be output
   > instead of the default 80. Setting it to 0 disables
   > diffs output.
   
   I'm not sure I entirely understand the problem.  If you expect lots of
   failures, but also don't want to see the test failures, what is the use of
   running the tests?  Why not run the subset you actually care about and expand
   that set as testing fixes bugs/issues?
   
   --
   Daniel Gustafsson
   
   
   
   
   

4. Re: Environment variable to disable diffs file output

   Ilya Cherdakov <i.cherdakov.pg@gmail.com> — 2026-04-07T08:31:03Z

   06.04.2026 16:47, Jelte Fennema-Nio wrote:
   
    > I'm fine with adding the abilitity to configure what pg_regress should
    > print, but it's unclear to me what's special about the diff output
    > compared to all the other output? i.e. what is the output you would
    > actually like to see for your use case? Piping everything to /dev/null
    > would silence all output except for the exit code, but I guess you
    > want some output. i.e. what do you do with the output that you get? Do
    > you only want to know which tests failed? If so, do you care about > 
   which tests are passing?
   
   Yes, redirecting all output to /dev/null isn't exactly what I need.
   
   Take a specific case, for example:
   When making numerous changes to tests as part of extensive stability
   testing (specifically, investigating crashes), the majority of test
   files may be modified. This results in diffs output for practically
   every single test, which turns into an unreadable jumble during the
   test run. In this case, I am not interested in all the diffs
   the ones associated with a crash. I can inspect those specific cases
   manually later, without needing the diffs output. Therefore, a flag
   like `PG_REGRESS_DIFF_OPTS='q'` does not suit my needs. And to find
   out which tests caused the crash (exit code 1 or 2) I need the
   entire output.
   
   06.04.2026 21:11, Daniel Gustafsson wrote:
    > I'm not sure I entirely understand the problem. If you expect lots of
    > failures, but also don't want to see the test failures, what is the 
   use of
    > running the tests? Why not run the subset you actually care about and 
   expand
    > that set as testing fixes bugs/issues?
   
   As part of exploratory testing:
   1. Output mismatches are considered normal behavior.
   2. Exploratory testing almost always affects all tests. Cases where
   it is necessary to run a small subset of tests are rare.
   
   Another case where multiple tests may fail is testing a patch that
   changes cluster parameters.For example, a patch for the scheduler
   has been released, and I need to ensure that it doesn't cause crashes
   when changing the 'random_page_cost' parameter. This parameter
   significantly changes the plan output, leading to multiple crashes and,
   consequently, the diffs output. While I'm not interested in the diffs
   themselves, I do want to know that there haven't been any crashes.
   In this case, we need to run not just a small group of tests,
   but everything we have.
   
   These are just a couple of examples where disabling diffs output
   would be useful.
   
   ---
   
   Also, if the diffs within a single directory run are very large,
   the output starts to become cluttered with lines like:
   
        #(diff output truncated and silencing output for
                                further failing tests...)
   
   Which also creates confusion and interferes with output analysis.
   Example
   
   #<long diffs output>
   not ok 1     - test_setup                                133 ms
   # parallel group (20 tests, in groups of 1):  boolean char name ...
   # (diff output truncated and silencing output for further failing tests...)
   not ok 2     + boolean                                    14 ms
   # (diff output truncated and silencing output for further failing tests...)
   not ok 3     + char                                        8 ms
   # (diff output truncated and silencing output for further failing tests...)
   not ok 4     + name                                        8 ms
   # (diff output truncated and silencing output for further failing tests...)
   <etc.>
   
   ---
   Best regards,
   Ilya Cherdakov
   Postgres Professional: https://postgrespro.com