Fix pgbench timestamp bugs.

Commit 547f04e7 changed pgbench to use microsecond accounting, but
introduced a couple of logging and aggregation bugs:

1.  We print Unix epoch timestamps so that you can correlate them with
other logs, but these were inadvertently changed to use a
system-dependent reference epoch.  Compute Unix timestamps, and begin
aggregation intervals on the boundaries of whole Unix epoch seconds, as
before.

2.  The user-supplied aggregation interval needed to be scaled.

Back-patch to 14.

Author: Fabien COELHO <coelho@cri.ensmp.fr>
Author: Yugo NAGATA <nagata@sraoss.co.jp>
Author: Kyotaro Horiguchi <horikyota.ntt@gmail.com>
Reported-by: YoungHwan Joo <rulyox@gmail.com>
Reported-by: Gregory Smith <gregsmithpgsql@gmail.com>
Discussion: https://postgr.es/m/CAF7igB1r6wRfSCEAB-iZBKxkowWY6%2BdFF2jObSdd9%2BiVK%2BvHJg%40mail.gmail.com
Discussion: https://postgr.es/m/CAHLJuCW_8Vpcr0%3Dt6O_gozrg3wXXWXZXDioYJd3NhvKriqgpfQ%40mail.gmail.com

src/bin/pgbench/pgbench.c

@@ -343,6 +343,12 @@ typedef struct StatsData
 	SimpleStats lag;
 } StatsData;
 
+/*
+ * For displaying Unix epoch timestamps, as some time functions may have
+ * another reference.
+ */
+pg_time_usec_t epoch_shift;
+
 /*
  * Struct to keep random state.
  */
@@ -3772,16 +3778,17 @@ executeMetaCommand(CState *st, pg_time_usec_t *now)
  * Print log entry after completing one transaction.
  *
  * We print Unix-epoch timestamps in the log, so that entries can be
- * correlated against other logs.  On some platforms this could be obtained
- * from the caller, but rather than get entangled with that, we just eat
- * the cost of an extra syscall in all cases.
+ * correlated against other logs.
+ *
+ * XXX We could obtain the time from the caller and just shift it here, to
+ * avoid the cost of an extra call to pg_time_now().
  */
 static void
 doLog(TState *thread, CState *st,
 	  StatsData *agg, bool skipped, double latency, double lag)
 {
 	FILE	   *logfile = thread->logfile;
-	pg_time_usec_t now = pg_time_now();
+	pg_time_usec_t now = pg_time_now() + epoch_shift;
 
 	Assert(use_log);
 
@@ -3796,17 +3803,19 @@ doLog(TState *thread, CState *st,
 	/* should we aggregate the results or not? */
 	if (agg_interval > 0)
 	{
+		pg_time_usec_t next;
+
 		/*
 		 * Loop until we reach the interval of the current moment, and print
 		 * any empty intervals in between (this may happen with very low tps,
 		 * e.g. --rate=0.1).
 		 */
 
-		while (agg->start_time + agg_interval <= now)
+		while ((next = agg->start_time + agg_interval * INT64CONST(1000000)) <= now)
 		{
 			/* print aggregated report to logfile */
 			fprintf(logfile, INT64_FORMAT " " INT64_FORMAT " %.0f %.0f %.0f %.0f",
-					agg->start_time,
+					agg->start_time / 1000000,	/* seconds since Unix epoch */
 					agg->cnt,
 					agg->latency.sum,
 					agg->latency.sum2,
@@ -3825,7 +3834,7 @@ doLog(TState *thread, CState *st,
 			fputc('\n', logfile);
 
 			/* reset data and move to next interval */
-			initStats(agg, agg->start_time + agg_interval);
+			initStats(agg, next);
 		}
 
 		/* accumulate the current transaction */
@@ -5458,7 +5467,8 @@ printProgressReport(TState *threads, int64 test_start, pg_time_usec_t now,
 
 	if (progress_timestamp)
 	{
-		snprintf(tbuf, sizeof(tbuf), "%.3f s", PG_TIME_GET_DOUBLE(now));
+		snprintf(tbuf, sizeof(tbuf), "%.3f s",
+				 PG_TIME_GET_DOUBLE(now + epoch_shift));
 	}
 	else
 	{
@@ -5808,6 +5818,14 @@ main(int argc, char **argv)
 	char	   *env;
 
 	int			exit_code = 0;
+	struct timeval tv;
+
+	/*
+	 * Record difference between Unix time and instr_time time.  We'll use
+	 * this for logging and aggregation.
+	 */
+	gettimeofday(&tv, NULL);
+	epoch_shift = tv.tv_sec * INT64CONST(1000000) + tv.tv_usec - pg_time_now();
 
 	pg_logging_init(argv[0]);
 	progname = get_progname(argv[0]);
@@ -6637,7 +6655,14 @@ threadRun(void *arg)
 	thread->bench_start = start;
 	thread->throttle_trigger = start;
 
-	initStats(&aggs, start);
+	/*
+	 * The log format currently has Unix epoch timestamps with whole numbers
+	 * of seconds.  Round the first aggregate's start time down to the nearest
+	 * Unix epoch second (the very first aggregate might really have started a
+	 * fraction of a second later, but later aggregates are measured from the
+	 * whole number time that is actually logged).
+	 */
+	initStats(&aggs, (start + epoch_shift) / 1000000 * 1000000);
 	last = aggs;
 
 	/* loop till all clients have terminated */