Re: maximum number of backtrace frames logged by backtrace_functions

On 03.02.22 06:33, Fujii Masao wrote:
> I encountered the "more than 100 backtrace frames" case when 
> investigating the bug of pg_log_query_plan() patch [1]. Since the 
> function that the patch added can be called repeatedly during call to 
> that function, the backtrace became larger than 100. I think this is not 
> general case, so basically 100 sounds enough limit size to me.
> 
> OTOH I think it's helpful if the limit is documented when I occasionally 
> encounter the case and want to understand why all backtrace frames are 
> not logged.

How about we issue a message when the backtrace is cut off.  Then it's 
immediately visible to the user, instead of hidden away somewhere in the 
documentation.  Something like this (untested):

diff --git a/src/backend/utils/error/elog.c b/src/backend/utils/error/elog.c
index 7402696986..3777dff030 100644
--- a/src/backend/utils/error/elog.c
+++ b/src/backend/utils/error/elog.c
@@ -967,6 +967,8 @@ set_backtrace(ErrorData *edata, int num_skip)
          for (int i = num_skip; i < nframes; i++)
              appendStringInfo(&errtrace, "\n%s", strfrms[i]);
          free(strfrms);
+        if (nframes >= lengthof(buf))
+            appendStringInfo(&errtrace, "\n(backtrace limited to %zu frames)", 
lengthof(buf));
      }
  #else
      appendStringInfoString(&errtrace,