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Re: [Proposal] Adding Log File Capability to pg_createsubscriber

Peter Smith <smithpb2250@gmail.com>

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From: Peter Smith <smithpb2250@gmail.com>
To: Gyan Sreejith <gyan.sreejith@gmail.com>
Cc: pgsql-hackers@lists.postgresql.org, vignesh C <vignesh21@gmail.com>
Date: 2025-12-11T07:29:07Z
Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. pg_createsubscriber: Don't use MAXPGPATH

  2. pg_createsubscriber: Remove separate logfile_open() function

  3. pg_createsubscriber: Use logging.c log file callback

  4. Add log file support to logging.c

  5. pg_createsubscriber: Add -l/--logdir option to redirect output to files.

  6. pg_createsubscriber: Introduce module-specific logging functions.

On Wed, Dec 10, 2025 at 9:17 AM Gyan Sreejith <gyan.sreejith@gmail.com> wrote:
>
> Background:
>
> pg_createsubscriber currently outputs all messages (internal validation messages, standby server start/stop logs, recovery progress output, and output from utilities) directly to the console. As a result, users may find debugging and handling errors difficult. It would be more convenient if messages were separated and stored in different log files. There is already a similar implementation in pg_upgrade.
>
> Proposed Solution:
>
> Based on issues mentioned previously, I would like to propose a new argument -l <logdir> which can be specified for pg_createsubscriber. Using it would create the following log files:
>
> logdir/pg_createsubscriber_server.log which captures all logs related to starting and stopping the standby server.
>
> logdir/pg_createsubscriber_resetwal.log which captures the output of pg_resetwal
>
> logdir/pg_createsubscriber_internal.log which captures internal diagnostic output from pg_createsubscriber (validations, checks, etc.)
>
> Overall, this proposed solution could make the pg_createsubscriber command output messages more organized. The command would be easier to use as users will only have to read individual log files rather than parse through lots of possibly irrelevant output messages. I have attached the patch for this change.
>
> Special thanks to Vignesh C. for his offlist guidance on this project.
>
>
> Regards, Gyan Sreejith
>

Hi Gyan.

I haven't yet looked at this patch in any detail, but here are some
quick comments:

======

1.
+ printf(_("  -l, --logdir=LOGDIR             location for the new log
directory\n"));

The patch is missing SGML docs updates for pg_createsubscriber new
option, and any explanation of the split of logfiles.

2.
I might be mistaken, but IIUC it seems the splitting of the logfile
only works when --logdir is specified. Is that correct?
Why should --logdir have any side-effect other than assigning the log
destination folder?

======
Kind Regards,
Peter Smith.
Fujitsu Australia