diff --git a/src/bin/pgbench/pgbench.c b/src/bin/pgbench/pgbench.c
index 1fb4ae46d5..d44cfdab49 100644
--- a/src/bin/pgbench/pgbench.c
+++ b/src/bin/pgbench/pgbench.c
@@ -299,7 +299,7 @@ typedef enum
 	 */
 	CSTATE_ABORTED,
 	CSTATE_FINISHED
-}	ConnectionStateEnum;
+} ConnectionStateEnum;
 
 /*
  * Connection state.
@@ -4420,43 +4420,43 @@ threadRun(void *arg)
 	initStats(&aggs, INSTR_TIME_GET_DOUBLE(thread->start_time));
 	last = aggs;
 
-	/* initialize explicitely the state machines */
+	/* explicitly initialize the state machines */
 	for (i = 0; i < nstate; i++)
 	{
 		state[i].state = CSTATE_CHOOSE_SCRIPT;
 	}
 
+	/* loop till all clients have terminated */
 	while (remains > 0)
 	{
 		fd_set		input_mask;
-		int			maxsock;	/* max socket number to be waited */
-		int64		now_usec = 0;
+		int			maxsock;	/* max socket number to be waited for */
 		int64		min_usec;
+		int64		now_usec = 0;		/* set this only if needed */
 
+		/* identify which client sockets should be checked for input */
 		FD_ZERO(&input_mask);
-
 		maxsock = -1;
 		min_usec = PG_INT64_MAX;
 		for (i = 0; i < nstate; i++)
 		{
 			CState	   *st = &state[i];
-			int			sock;
 
 			if (st->state == CSTATE_THROTTLE && timer_exceeded)
 			{
-				/* interrupt client which has not started a transaction */
+				/* interrupt client that has not started a transaction */
 				st->state = CSTATE_FINISHED;
-				remains--;
 				PQfinish(st->con);
 				st->con = NULL;
-				continue;
+				remains--;
 			}
 			else if (st->state == CSTATE_SLEEP || st->state == CSTATE_THROTTLE)
 			{
 				/* a nap from the script, or under throttling */
-				int			this_usec;
+				int64		this_usec;
 
-				if (min_usec == PG_INT64_MAX)
+				/* get current time if needed */
+				if (now_usec == 0)
 				{
 					instr_time	now;
 
@@ -4464,6 +4464,7 @@ threadRun(void *arg)
 					now_usec = INSTR_TIME_GET_MICROSEC(now);
 				}
 
+				/* min_usec should be the minimum delay across all clients */
 				this_usec = (st->state == CSTATE_SLEEP ?
 							 st->sleep_until : st->txn_scheduled) - now_usec;
 				if (min_usec > this_usec)
@@ -4475,22 +4476,26 @@ threadRun(void *arg)
 				 * waiting for result from server - nothing to do unless the
 				 * socket is readable
 				 */
-				sock = PQsocket(st->con);
+				int			sock = PQsocket(st->con);
+
 				if (sock < 0)
 				{
-					fprintf(stderr, "invalid socket: %s", PQerrorMessage(st->con));
+					fprintf(stderr, "invalid socket: %s",
+							PQerrorMessage(st->con));
 					goto done;
 				}
 
 				FD_SET(sock, &input_mask);
-
 				if (maxsock < sock)
 					maxsock = sock;
-				break;
 			}
-			else if (st->state != CSTATE_ABORTED && st->state != CSTATE_FINISHED)
+			else if (st->state != CSTATE_ABORTED &&
+					 st->state != CSTATE_FINISHED)
 			{
-				/* the connection is ready to run */
+				/*
+				 * This client thread is ready to do something, so we don't
+				 * want to wait.  No need to examine additional clients.
+				 */
 				min_usec = 0;
 				break;
 			}
@@ -4515,9 +4520,10 @@ threadRun(void *arg)
 		}
 
 		/*
-		 * Sleep until we receive data from the server, or a nap-time
-		 * specified in the script ends, or it's time to print a progress
-		 * report.
+		 * If no clients are ready to execute actions, sleep until we receive
+		 * data from the server, or a nap-time specified in the script ends,
+		 * or it's time to print a progress report.  Update input_mask to show
+		 * which client(s) received data.
 		 */
 		if (min_usec > 0 && maxsock != -1)
 		{
@@ -4536,21 +4542,29 @@ threadRun(void *arg)
 			if (nsocks < 0)
 			{
 				if (errno == EINTR)
+				{
+					/* On EINTR, go back to top of loop */
 					continue;
+				}
 				/* must be something wrong */
 				fprintf(stderr, "select() failed: %s\n", strerror(errno));
 				goto done;
 			}
 		}
+		else
+		{
+			/* If we didn't call select(), don't try to read any data */
+			FD_ZERO(&input_mask);
+		}
 
 		/* ok, advance the state machine of each connection */
 		for (i = 0; i < nstate; i++)
 		{
 			CState	   *st = &state[i];
-			bool		ready;
 
-			if (st->state == CSTATE_WAIT_RESULT && st->con)
+			if (st->state == CSTATE_WAIT_RESULT)
 			{
+				/* don't call doCustom unless data is available */
 				int			sock = PQsocket(st->con);
 
 				if (sock < 0)
@@ -4560,22 +4574,24 @@ threadRun(void *arg)
 					goto done;
 				}
 
-				ready = FD_ISSET(sock, &input_mask);
+				if (!FD_ISSET(sock, &input_mask))
+					continue;
 			}
-			else if (st->state == CSTATE_FINISHED || st->state == CSTATE_ABORTED)
-				ready = false;
-			else
-				ready = true;
-
-			if (ready)
+			else if (st->state == CSTATE_FINISHED ||
+					 st->state == CSTATE_ABORTED)
 			{
-				doCustom(thread, st, &aggs);
-				if (st->state == CSTATE_FINISHED || st->state == CSTATE_ABORTED)
-					remains--;
+				/* this client is done, no need to consider it anymore */
+				continue;
 			}
+
+			doCustom(thread, st, &aggs);
+
+			/* If doCustom changed client to finished state, reduce remains */
+			if (st->state == CSTATE_FINISHED || st->state == CSTATE_ABORTED)
+				remains--;
 		}
 
-		/* progress report by thread 0 for all threads */
+		/* progress report is made by thread 0 for all threads */
 		if (progress && thread->tid == 0)
 		{
 			instr_time	now_time;