Function write_stderr

src/backend/utils/error/elog.c:4976–5057

* Write errors to stderr (or by equal means when stderr is * not available). Used before ereport/elog can be used * safely (memory context, GUC load etc) */

 * safely (memory context, GUC load etc)
 */
void
write_stderr(const char *fmt,...)
{
	va_list		ap;

#ifdef WIN32
	char		errbuf[2048];	/* Arbitrary size? */
#endif

	fmt = _(fmt);

	va_start(ap, fmt);

	if (Logging_collector && gp_log_format == 1)
	{
		char		errbuf[2048];		/* Arbitrary size? */

		vsnprintf(errbuf, sizeof(errbuf), fmt, ap);

		if (MyBackendType != B_LOGGER)
		{
			/* Write the message in the CSV format */
			write_message_to_server_log(LOG,
										0,
										errbuf,
										NULL,
										NULL,
										NULL,
										0,
										0,
										NULL,
										NULL,
										NULL,
										false,
										NULL,
										0,
										0,
										true,
										NULL,
										false);
		}
		else
		{
			ErrorData edata;
			memset(&edata, 0, sizeof(ErrorData));
			edata.elevel = LOG;
			edata.message = errbuf;
			edata.omit_location = true;
			if (redirection_done)
				write_syslogger_in_csv(&edata, true);
			else
				write_syslogger_in_csv(&edata, false);
		}

		va_end(ap);
		return;
	}