Re: maximum number of backtrace frames logged by backtrace_functions
От | Yugo NAGATA |
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Тема | Re: maximum number of backtrace frames logged by backtrace_functions |
Дата | |
Msg-id | 20220302154704.516286896b6f8ca924b2e384@sraoss.co.jp обсуждение исходный текст |
Ответ на | Re: maximum number of backtrace frames logged by backtrace_functions (Fujii Masao <masao.fujii@oss.nttdata.com>) |
Список | pgsql-docs |
On Sat, 19 Feb 2022 01:05:04 +0900 Fujii Masao <masao.fujii@oss.nttdata.com> wrote: > > > On 2022/02/18 19:59, Peter Eisentraut wrote: > > On 18.02.22 09:24, Fujii Masao wrote: > >> Or even backtrace should be logged by write_stderr() so that it's written to eventlog if necessary? I just wonder whybacktrace_symbols_fd() is used only in ExceptionalCondition(). > > > > Probably because it was simpler. It would also make sense to convert the whole thing to use write_stderr() consistently. > +1 > Attached is the updated version of the patch that uses write_stderr() to log the backtrace in assertion failure case. > > + if (nframes >= lengthof(buf)) > + appendStringInfo(&errtrace, "\n(backtrace limited to %zu frames)", > + lengthof(buf)); > > I found this doesn't work on FreeBSD, at least FreeBSD 13 that cfbot uses on Cirrus CI. When the backtrace is larger than100, on FreeBSD, backtrace() seems to write the *99* (not 100) most recent function calls to the buffer. That is, thevariable "nframes" is 99 while lengthof(buf) indicates 100. So the above message about backtrace limit will never be loggedon FreeBSD. OTOH, on Linux and MacOS, backtrace() writes the 100 most recent function calls. I'm not sure if such abehavior on FreeBSD is expected or a bug. > > To issue the message whatever OS is, probably we need to modify set_backtrace() as follows, for example. But is this overkill?Thought? > > > - void *buf[100]; > +#define BACKTRACE_MAX_FRAMES 100 > + void *buf[BACKTRACE_MAX_FRAMES + 1]; > int nframes; > char **strfrms; > > nframes = backtrace(buf, lengthof(buf)); > + if (nframes > BACKTRACE_MAX_FRAMES) > + nframes = BACKTRACE_MAX_FRAMES; > strfrms = backtrace_symbols(buf, nframes); > if (strfrms == NULL) > return; > > for (int i = num_skip; i < nframes; i++) > appendStringInfo(&errtrace, "\n%s", strfrms[i]); > + if (nframes >= BACKTRACE_MAX_FRAMES) > + appendStringInfo(&errtrace, "\n(backtrace limited to %d frames)", > + BACKTRACE_MAX_FRAMES); I think it would be better that users can get the same results in different OS as as possible. I have another comment. When the backtrace is output from elog, two rows are skipped by num_skip and only 98 frames will appear even though it is said "backtrace limited to 100 frames". So, how about reporting the limiting number subtracted by num_skip, like this: if (nframes >= lengthof(buf)) appendStringInfo(&errtrace, "\n(backtrace limited to %zu frames)", lengthof(buf) - num_skip); or if (nframes >= BACKTRACE_MAX_FRAMES) appendStringInfo(&errtrace, "\n(backtrace limited to %d frames)", BACKTRACE_MAX_FRAMES - num_skip); Regards, Yugo Nagata -- Yugo NAGATA <nagata@sraoss.co.jp>
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