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From: Fujii Masao <[email protected]>
To: Tom Lane <[email protected]>
To: Peter Eisentraut <[email protected]>
Cc: [email protected]
Subject: Re: maximum number of backtrace frames logged by backtrace_functions
Date: Fri, 4 Feb 2022 09:48:58 +0900
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
References: <[email protected]>
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On 2022/02/03 23:48, Tom Lane wrote:
> Peter Eisentraut <[email protected]> writes:
>> 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):
> 
> +1 for idea (I didn't test it either).

+1. I made this change to the patch and confirmed that it worked fine.

For the record, I tested that by setting backtrace_functions to 'pg_wal_replay_pause' and executing it. This function will report an error when it's called not during recovery.

In the test, "SELECT pg_wal_replay_pause()" caused backtrace but "backtrace limited to %zu frames" message was not output because the number of backtrace frames was less than 100.

Then I created the function "foo" as follows and executed "SELECT foo(0)" to generate more than 100 backtrace frames. In this case "backtrace limited to %zu frames" message was successfully output.

CREATE FUNCTION foo (x int) RETURNS void AS $$
BEGIN
   IF x = 10 THEN
     PERFORM pg_wal_replay_pause();
   ELSE
     PERFORM foo(x + 1);
   END IF;
END;
$$ LANGUAGE plpgsql;


> Is "nframes" useful enough to
> include in the report?

Probably No because "nframes" is equal to "lengthof(buf)" in the case where more than 100 frames are generated.

Regards,

-- 
Fujii Masao
Advanced Computing Technology Center
Research and Development Headquarters
NTT DATA CORPORATION
diff --git a/src/backend/utils/error/elog.c b/src/backend/utils/error/elog.c
index 7402696986..9933386959 100644
--- a/src/backend/utils/error/elog.c
+++ b/src/backend/utils/error/elog.c
@@ -966,6 +966,9 @@ set_backtrace(ErrorData *edata, int num_skip)
 
 		for (int i = num_skip; i < nframes; i++)
 			appendStringInfo(&errtrace, "\n%s", strfrms[i]);
+		if (nframes >= lengthof(buf))
+			appendStringInfo(&errtrace, "\n(backtrace limited to %zu frames)",
+							 lengthof(buf));
 		free(strfrms);
 	}
 #else


Attachments:

  [text/plain] backtrace_limit_report.patch (510B, 2-backtrace_limit_report.patch)
  download | inline diff:
diff --git a/src/backend/utils/error/elog.c b/src/backend/utils/error/elog.c
index 7402696986..9933386959 100644
--- a/src/backend/utils/error/elog.c
+++ b/src/backend/utils/error/elog.c
@@ -966,6 +966,9 @@ set_backtrace(ErrorData *edata, int num_skip)
 
 		for (int i = num_skip; i < nframes; i++)
 			appendStringInfo(&errtrace, "\n%s", strfrms[i]);
+		if (nframes >= lengthof(buf))
+			appendStringInfo(&errtrace, "\n(backtrace limited to %zu frames)",
+							 lengthof(buf));
 		free(strfrms);
 	}
 #else

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