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Message-ID: <e312116f-9c44-b7f6-3cfc-4c67f50bbbc7@oss.nttdata.com>
Date: Fri, 4 Feb 2022 09:48:58 +0900
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Subject: Re: maximum number of backtrace frames logged by backtrace_functions
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To: Tom Lane <tgl@sss.pgh.pa.us>,
 Peter Eisentraut <peter.eisentraut@enterprisedb.com>
Cc: pgsql-docs@lists.postgresql.org
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 <252159.1643899696@sss.pgh.pa.us>
From: Fujii Masao <masao.fujii@oss.nttdata.com>
In-Reply-To: <252159.1643899696@sss.pgh.pa.us>
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On 2022/02/03 23:48, Tom Lane wrote:
> Peter Eisentraut <peter.eisentraut@enterprisedb.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
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