Re: [HACKERS] Runtime Partition Pruning
От | Tomas Vondra |
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Тема | Re: [HACKERS] Runtime Partition Pruning |
Дата | |
Msg-id | 20190524224239.jnzgkszsuaxwnvji@development обсуждение исходный текст |
Ответ на | Re: [HACKERS] Runtime Partition Pruning (Andres Freund <andres@anarazel.de>) |
Ответы |
Re: [HACKERS] Runtime Partition Pruning
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Список | pgsql-hackers |
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 <andres@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
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