Re: maximum number of backtrace frames logged by backtrace_functions

On 2022/02/03 23:48, Tom Lane wrote:
> Peter Eisentraut <peter(dot)eisentraut(at)enterprisedb(dot)com> 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