Re: PATCH: backtraces for error messages

On 21 June 2018 at 19:09, Kyotaro HORIGUCHI <horiguchi(dot)kyotaro(at)lab(dot)ntt(dot)co(dot)jp
> wrote:

I think this for assertion failure is no problem but I'm not sure
> for other cases.

I think it's pretty strongly desirable for PANIC.

> We could set proper context description or other
> additional information in error messages before just dumping a
> trace for known cases.
>

Yeah. The trouble there is that there are a _lot_ of places to touch for
such things, and inevitably the one you really want to see will be
something that didn't get suitably annotated.

> Since PG9.5 RPMs are complied with --enable-dtrace so we could
> use system tap to insert the stack-trace stuff. Additional
> built-in probe in error reporting system or assertions would make
> this pluggable.
>

I don't bother with SystemTAP anymore; perf does the job for most purposes.

You can use --enable-dtrace SDTs with Perf fine. I wrote it up for Pg at
https://wiki.postgresql.org/wiki/Profiling_with_perf#PostgreSQL_pre-defined_tracepoint_events
.

Dynamic tracepoints are also very useful.

Both require debuginfo, but so does outputting of symbolic stacks per my
patch.

(That reminds me, I need to chat with Devrim about creating a longer lived
debuginfo + old versions rpms repo for Pg its self, if not the accessory
bits and pieces. I'm so constantly frustrated by not being able to get
needed debuginfo packages to investigate some core or running system
problem because they've been purged from the PGDG yum repo as soon as a new
version comes out.)

--
Craig Ringer http://www.2ndQuadrant.com/
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