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Date: Fri, 3 Jul 2026 09:34:22 +0200
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Subject: Re: Truncate logs by max_log_size
To: Fujii Masao <masao.fujii@gmail.com>
Cc: Maxym Kharchenko <maxymkharchenko@gmail.com>,
 Kirill Reshke <reshkekirill@gmail.com>, =?UTF-8?Q?=C3=81lvaro_Herrera?=
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 Kirill Gavrilov <diphantxm@gmail.com>,
 "Andrey M. Borodin" <x4mmm@yandex-team.ru>, Euler Taveira
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From: Jim Jones <jim.jones@uni-muenster.de>
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On 03/07/2026 02:56, Fujii Masao wrote:
> Thanks for the review! I've pushed the patch.

Awesome. Thanks!

> While working on it, I found a few possible follow-up improvements.
> 
> (1)
> When log_statement is enabled, executing a prepared statement logs the
> prepared query in a DETAIL message. For example:
> 
>     =# SET log_statement_max_length TO 10;
>     =# PREPARE test AS SELECT * FROM pgbench_accounts WHERE aid = $1;
>     LOG:  statement: PREPARE te
>     =# EXECUTE test(1);
>     LOG:  statement: EXECUTE te
>     DETAIL:  prepare: PREPARE test AS SELECT * FROM pgbench_accounts
> WHERE aid = $1;
> 
> Should log_statement_max_length also apply to such query string in the
> DETAIL message?
> 
> (2)
> When a bind parameter is truncated by
> log_parameter_max_length, an ellipsis (...) is appended:
> 
>     =# SET log_parameter_max_length TO 5;
>     =# SELECT $1::text \bind 'abcdefghijk' \g
>     LOG:  execute <unnamed>: SELECT $1::text
>     DETAIL:  Parameters: $1 = 'abcde...'
> 
> Would it make sense for log_statement_max_length to append an
> ellipsis as well, so that users can easily tell when a statement has
> been truncated?

+1
Nice additions -- the feature gap is obvious, IMHO.

Are you planning to work on it? I'm drowning in work right now and can
only jump on it next week.

> (3)
> + query_len = strlen(query);
> 
> truncate_query_log() uses strlen() only to determine whether the
> query exceeds log_statement_max_length. Since the query can be very
> large, would it be better to use
> 
>     strnlen(query, log_statement_max_length + MAX_MULTIBYTE_CHAR_LEN)
> 
> instead, to avoid scanning the entire string?

I'm not so sure about this one. At this point, isn't "query" already \0
terminated? I'm also wondering if it could affect pg_mbcliplen() down
the road, since strnlen() can return a different value
(log_statement_max_length + MAX_MULTIBYTE_CHAR_LEN) on large queries --
not tested yet.

Thanks!

Best, Jim