Use carriage returns for data insertion logs in pgbench on terminal

This is similar to what pg_basebackup and pg_rewind do when reporting
cumulative data, and that's more user-friendly.  Carriage returns are
now used when stderr points to a terminal, and newlines are used in
other cases, like a redirection to a log file.

Author: Amit Langote
Reviewed-by: Fabien Coelho
Discussion: https://postgr.es/m/CA+HiwqFNwEjPeVaQsp2L7DyCPv1Eg1guwhrVhzMYqUJUk8ULKg@mail.gmail.com

src/bin/pgbench/pgbench.c

@@ -3835,6 +3835,9 @@ initGenerateDataClientSide(PGconn *con)
 				remaining_sec;
 	int			log_interval = 1;
 
+	/* Stay on the same line if reporting to a terminal */
+	char		eol = isatty(fileno(stderr)) ? '\r' : '\n';
+
 	fprintf(stderr, "generating data (client-side)...\n");
 
 	/*
@@ -3910,10 +3913,10 @@ initGenerateDataClientSide(PGconn *con)
 			elapsed_sec = INSTR_TIME_GET_DOUBLE(diff);
 			remaining_sec = ((double) scale * naccounts - j) * elapsed_sec / j;
 
-			fprintf(stderr, INT64_FORMAT " of " INT64_FORMAT " tuples (%d%%) done (elapsed %.2f s, remaining %.2f s)\n",
+			fprintf(stderr, INT64_FORMAT " of " INT64_FORMAT " tuples (%d%%) done (elapsed %.2f s, remaining %.2f s)%c",
 					j, (int64) naccounts * scale,
 					(int) (((int64) j * 100) / (naccounts * (int64) scale)),
-					elapsed_sec, remaining_sec);
+					elapsed_sec, remaining_sec, eol);
 		}
 		/* let's not call the timing for each row, but only each 100 rows */
 		else if (use_quiet && (j % 100 == 0))
@@ -3927,16 +3930,19 @@ initGenerateDataClientSide(PGconn *con)
 			/* have we reached the next interval (or end)? */
 			if ((j == scale * naccounts) || (elapsed_sec >= log_interval * LOG_STEP_SECONDS))
 			{
-				fprintf(stderr, INT64_FORMAT " of " INT64_FORMAT " tuples (%d%%) done (elapsed %.2f s, remaining %.2f s)\n",
+				fprintf(stderr, INT64_FORMAT " of " INT64_FORMAT " tuples (%d%%) done (elapsed %.2f s, remaining %.2f s)%c",
 						j, (int64) naccounts * scale,
-						(int) (((int64) j * 100) / (naccounts * (int64) scale)), elapsed_sec, remaining_sec);
+						(int) (((int64) j * 100) / (naccounts * (int64) scale)), elapsed_sec, remaining_sec, eol);
 
 				/* skip to the next interval */
 				log_interval = (int) ceil(elapsed_sec / LOG_STEP_SECONDS);
 			}
 		}
-
 	}
+
+	if (eol != '\n')
+		fputc('\n', stderr);	/* Need to move to next line */
+
 	if (PQputline(con, "\\.\n"))
 	{
 		fprintf(stderr, "very last PQputline failed\n");