Re: [HACKERS] src/test/subscription/t/002_types.pl hanging onparticular environment

On 2017-09-19 17:20:49 -0400, Tom Lane wrote:
> Thomas Munro <thomas.munro@enterprisedb.com> writes:
> > This type of violent shutdown seems to be associated with occasional
> > corruption of .gcda files (the files output by GCC coverage builds).
> > The symptoms are that if you use --enable-coverage and make
> > check-world you'll very occasionally get a spurious TAP test failure
> > like this:
> 
> > #   Failed test 'pg_ctl start: no stderr'
> > #   at /home/travis/build/postgresql-cfbot/postgresql/src/bin/pg_ctl/../../../src/test/perl/TestLib.pm
> > line 301.
> > #          got:
> > 'profiling:/home/travis/build/postgresql-cfbot/postgresql/src/backend/nodes/copyfuncs.gcda:Merge
> > mismatch for function 94
> > # '
> > #     expected: ''
> 
> > I'm not sure of the exact mechanism though.  GCC supplies a function
> > __gcov_flush() that normally runs at exit or execve, so if you're
> > killed without reaching those you don't get any .gcda data.  Perhaps
> > we are in exit (or fork/exec) partway through writing out coverage
> > data in __gcov_flush(), and at that moment we are killed.  Then a
> > subsequent run of instrumented code will find the half-written file
> > and print the "Merge mismatch" message.

Note that newer gcc's (7+) have a feature to avoid such corruption, by
renaming the files atomically. Possibly the fix here is to just upgrade
to such a version...

Greetings,

Andres Freund


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