Re: How to debugging a an external C function(IMMUTABLE STRICT ) - Mailing list pgsql-general

From Tom Lane
Subject Re: How to debugging a an external C function(IMMUTABLE STRICT )
Date
Msg-id 10375.1330278418@sss.pgh.pa.us
Whole thread Raw
In response to How to debugging a an external C function(IMMUTABLE STRICT )  (Dave Potts <dave.potts@pinan.co.uk>)
List pgsql-general
Dave Potts <dave.potts@pinan.co.uk> writes:
> I have written an external C function to be called by postgres called
> using the LANGUAGE 'C' IMMUNTABLE STRICT interface
> Most of the time when call it, I get the expected results.  Some times I
> get random rubbish in the result set.
> If there any debug support in Postgres to catch this type of thing?

You should pretty much always do development of any C code in a backend
built with --enable-cassert --enable-debug.  In particular that will
turn on clobbering of freed memory, which is really helpful in turning
some types of sometimes-failure into consistent failures that can be
debugged.  That might not be your problem here, but it's worth a try.

I also get the impression that the only debug technique you know about
is inserting printfs.  Learn to use gdb or another debugger to step
through your code --- the learning curve isn't that steep, and the
benefits numerous.  There's useful Postgres-specific info about using
gdb here:
http://wiki.postgresql.org/wiki/Getting_a_stack_trace_of_a_running_PostgreSQL_backend_on_Linux/BSD

            regards, tom lane

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