Message-ID: <b219d7c9-fb66-c762-ce90-ef20c0667a02@enterprisedb.com>
Date: Thu, 3 Feb 2022 10:30:00 +0100
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Subject: Re: maximum number of backtrace frames logged by backtrace_functions
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To: Fujii Masao <masao.fujii@oss.nttdata.com>, pgsql-docs@lists.postgresql.org
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 <b22cd3c0-d76b-0379-5971-8637b65b8e87@oss.nttdata.com>
From: Peter Eisentraut <peter.eisentraut@enterprisedb.com>
In-Reply-To: <b22cd3c0-d76b-0379-5971-8637b65b8e87@oss.nttdata.com>
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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,