On Fri, May 24, 2019 at 09:24:28AM -0700, Andres Freund wrote:
Hi,
On 2019-05-24 12:08:57 -0400, Tom Lane wrote:
Andres Freund <and...@anarazel.de> writes:
> On 2019-05-24 11:34:58 -0400, Tom Lane wrote:
>> Hmm, after some digging in the archives, the closest thing I can find
>> is this thread:
>>
https://www.postgresql.org/message-id/flat/CAMsr%2BYGL%2ByfWE%3DJvbUbnpWtrRZNey7hJ07%2BzT4bYJdVp4Szdrg%40mail.gmail.com
>> where we discussed using libunwind instead, but people didn't like
>> the extra dependency.
> Hm, I didn't actually see that much concern about that. I still think we
> should just go for libunwind.
Is it actually better?
I've not looked in a while, but I think at some point it was.
The basic problem with backtrace() is that it
only knows about global functions, and so reports call sites in static
functions as if they were in whatever global function physically precedes
the static one.
Does that depend on whether the program was compiled with
-fno-omit-frame-pointer? At least some distros now compile with frame
pointers enabled, to get reasonably fast perf profiles (at a basically
immeasurable slowdown, on modern-ish CPUs).
I doubt that, because if that was the case we'd not be able to get
accurate profiles from perf, no? And AFAICS that's not the case,
irrespectedly of whether -fno-omit-frame-pointer is used.
I think doing materially better requires depending on
debug symbols, which (at least in the Red Hat world) aren't going to
be there in a typical production situation.
It's still a lot easier to install debug symbols than to attach a
debugger and get a backtrace that way. Especially when the problem is
hard to reproduce.
Right. Debugger requires interaction with a running process, while
having it integrated would make that unnecessary.
But I think Peter also suggested this might require the ability to
selectively enable the backtraces, and I think he's right. I doubt we
want to log them for every log message, right?
regards
--
Tomas Vondra http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
