Re: pg_ctl start may return 0 even if the postmaster has been already started on Windows

Hi,

I'm reviewing patches in Commitfest 2024-07 from top to bottom:
https://commitfest.postgresql.org/48/

This is the 2st patch:
https://commitfest.postgresql.org/48/4573/

FYI: https://commitfest.postgresql.org/48/4681/ is my patch.

In <Zl5SC_kboY7i0AS8@paquier.xyz>
  "Re: pg_ctl start may return 0 even if the postmaster has been already started on Windows" on Tue, 4 Jun 2024
08:30:19+0900,
 
  Michael Paquier <michael@paquier.xyz> wrote:

> During a live review of this patch last week, as part of the Advanced
> Patch Workshop of pgconf.dev, it has been mentioned by Tom that we may
> be able to simplify the check on pmstart if the detection of the
> postmaster PID started by pg_ctl is more stable using the WIN32
> internals that this patch relies on.  I am not sure that this
> suggestion is right, though, because we should still care about the
> clock skew case as written in the surrounding comments?  Even if
> that's OK, I would assume that this should be an independent patch,
> written on top of the proposed v6-0001.

I reviewed the latest patch set and I felt different
impression.

start_postmaster() on Windows uses cmd.exe for redirection
based on the comment in the function:

> /*
>  * As with the Unix case, it's easiest to use the shell (CMD.EXE) to
>  * handle redirection etc.  Unfortunately CMD.EXE lacks any equivalent of
>  * "exec", so we don't get to find out the postmaster's PID immediately.
>  */

It seems that we can use redirection by CreateProcess()
family functions without cmd.exe based on the following
documentation:

https://learn.microsoft.com/en-us/windows/win32/procthread/creating-a-child-process-with-redirected-input-and-output

How about changing start_postmaster() for Windows to start
postgres.exe directly so that it returns the postgres.exe's
PID not cmd.exe's PID? If we can do it, we don't need
pgwin32_find_postmaster_pid() in the patch set.


Thanks,
-- 
kou