v2-0002-Implement-TimestampDifferenceMilliseconds.patch

From 23a8a967e806b76f3ed2f9078d6c9afdc7a8dc48 Mon Sep 17 00:00:00 2001
From: Alexey Kondratov <kondratov.aleksey@gmail.com>
Date: Mon, 9 Nov 2020 22:29:48 +0300
Subject: [PATCH v2 2/4] Implement TimestampDifferenceMilliseconds()

Many callers of TimestampDifference() actually want a difference
in milliseconds.  This new function allows them to get rid of
unnecessary (and frequently unsafe) calculations of milliseconds from
seconds and microseconds.
---
 src/backend/utils/adt/timestamp.c | 20 ++++++++++++++++++++
 src/include/utils/timestamp.h     |  2 ++
 2 files changed, 22 insertions(+)

diff --git a/src/backend/utils/adt/timestamp.c b/src/backend/utils/adt/timestamp.c
index ea0ada704f..7b28f070cc 100644
--- a/src/backend/utils/adt/timestamp.c
+++ b/src/backend/utils/adt/timestamp.c
@@ -1666,6 +1666,26 @@ TimestampDifference(TimestampTz start_time, TimestampTz stop_time,
 	}
 }
 
+/*
+ * TimestampDifferenceMilliseconds -- convert the difference between two
+ * 		timestamps into integer milliseconds.
+ *
+ * Both inputs must be ordinary finite timestamps (in current usage,
+ * they'll be results from GetCurrentTimestamp()).
+ *
+ * We expect start_time <= stop_time.  If not, we return zero.
+ */
+long
+TimestampDifferenceMilliseconds(TimestampTz start_time, TimestampTz stop_time)
+{
+	TimestampTz diff = stop_time - start_time;
+
+	if (diff <= 0)
+		return 0;
+	else
+		return (long) (diff / 1000);
+}
+
 /*
  * TimestampDifferenceExceeds -- report whether the difference between two
  *		timestamps is >= a threshold (expressed in milliseconds)
diff --git a/src/include/utils/timestamp.h b/src/include/utils/timestamp.h
index 16c3fd8ec9..d45bf2bb7b 100644
--- a/src/include/utils/timestamp.h
+++ b/src/include/utils/timestamp.h
@@ -72,6 +72,8 @@ extern TimestampTz GetSQLCurrentTimestamp(int32 typmod);
 extern Timestamp GetSQLLocalTimestamp(int32 typmod);
 extern void TimestampDifference(TimestampTz start_time, TimestampTz stop_time,
 								long *secs, int *microsecs);
+extern long TimestampDifferenceMilliseconds(TimestampTz start_time,
+											TimestampTz stop_time);
 extern bool TimestampDifferenceExceeds(TimestampTz start_time,
 									   TimestampTz stop_time,
 									   int msec);
-- 
2.19.1