Re: Fix for timestamp lag issue from emit_log_hook when GUC log_line_prefix has '%m'

Thanks Michael for the review. Agree with your comment on the patch.
updated the patch with recommended change.

Thanks,
Vinay

On Mon, Mar 11, 2024 at 1:13 PM Michael Paquier <michael(at)paquier(dot)xyz> wrote:

> On Sat, Mar 09, 2024 at 09:09:39PM +0530, Kambam Vinay wrote:
> > We observed a slight lag in timestamp for a few logs from the
> emit_log_hook
> > hook implementation when the log_line_prefix GUC has '%m'.
> >
> > Upon debugging, we found that the saved_timeval_set variable is set to
> > 'true' in get_formatted_log_time() but is not reset to 'false' until the
> > next call to send_message_to_server_log(). Due to this, saved_timeval_set
> > will be true during the execution of hook emit_log_hook() which prefixes
> > the saved timestamp 'saved_timeval' from the previous log line (our hook
> > implementation calls log_line_prefix()).
> >
> > Attached patch sets the saved_timeval_set to false before executing the
> > emit_log_hook()
>
> Indeed. If you rely on log_line_prefix() in your hook before the
> server side elog, the saved timestamp would not match with what could
> be computed in the follow-up send_message_to_server_log or
> send_message_to_frontend.
>
> Hmm. Shouldn't we remove the forced reset of formatted_log_time for
> the 'm' case in log_status_format() and remove the reset done at the
> beginning of send_message_to_server_log()? One problem with your
> patch is that we would still finish with a different saved_timeval in
> the hook and in send_message_to_server_log(), but we should do things
> so as the timestamps are the same for the whole duration of
> EmitErrorReport(), no? It seems to me that a more correct solution
> would be to reset saved_timeval_set and formatted_log_time[0] once
> before the hook, at the beginning of EmitErrorReport().
> --
> Michael
>