Re: [PATCH] Fixed creation of empty .log files during log rotation

On Tue, 2024-10-29 at 11:08 +0300, Арсений Косицын wrote:
>  log_destination = 'csvlog'
>  logging_collector = on
>  log_rotation_age = 1min
>  log_directory = '/home/user/builds/postgresql/log'
>
>  2) After starting the server, two files are being created in the directory with logs:
>
>  -rw------- 1 user user  1,4K oct 10 13:29 postgresql-2024-10-10_132907.csv
>  -rw------- 1 user user  172 oct 10 13:29 postgresql-2024-10-10_132907.log
>
>  3) The .log file is created anyway, regardless of the log_destination parameter.
>  [...]
>
>  Next, the stderr stream is redirected to a .csv file.
>
>  4) Now, logs are rotated once a minute (due to the set log_rotation_age parameter). Moreover, all
>  open log files are rotated, including the .log file that I wrote about above. New ones are being created
>  .csv and .log files. Logs themselves are sent to .csv, and nothing else is output to .log
>  and it remains empty:
>
>  --Fix:
>
>  To correct the situation, you can add a check for the "Log_destination" parameter in the "logfile_rotate()"
>  function of the "syslogger.c" module. Then only the logs specified in this parameter will be rotated.
> This is done in the proposed patch.

I see your point, but I am having doubts.

You say that the stderr stream is redirected to the CSV file, but that is not true.
Anything that a PostgreSQL process writes to stderr will still end up in the *.log file.
For example, any error message from the archive_command will end up there, not in the
CSV log.

I think that that is pretty useful.

Where do such messages end up with your patch?  I didn't test, but I guess they'll
just be written to the console and get lost.
The empty (or almost empty) *.log files are not pretty, but are they a problem
to solve at the price of losing potentially interesting information?

Yours,
Laurenz Albe