0001-UUDv7-fix-offset-computations-in-dates-after-2262.patch

From 8b52d0942f657c35e238bd95bd2d95aa5c4a5b2e Mon Sep 17 00:00:00 2001
From: Andrey Borodin <amborodin@acm.org>
Date: Fri, 31 Jan 2025 12:03:16 +0500
Subject: [PATCH] UUDv7: fix offset computations in dates after 2262

We used nanosecond representation of offsetted time values which
cannot be stored in 64-bit integer for dates significantly after
beginning of UNIX epoch. To prevent overflow we separate millisecond
part from nanoseconds, thus allowing us to store both parts in 64-bit
integers.
---
 src/backend/utils/adt/uuid.c | 26 ++++++++++++++------------
 1 file changed, 14 insertions(+), 12 deletions(-)

diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c
index 4f8402ef925..3349c2674c8 100644
--- a/src/backend/utils/adt/uuid.c
+++ b/src/backend/utils/adt/uuid.c
@@ -68,7 +68,7 @@ static int	uuid_fast_cmp(Datum x, Datum y, SortSupport ssup);
 static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup);
 static Datum uuid_abbrev_convert(Datum original, SortSupport ssup);
 static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version);
-static inline int64 get_real_time_ns_ascending();
+static inline uint64 get_real_time_ns_ascending();
 
 Datum
 uuid_in(PG_FUNCTION_ARGS)
@@ -476,11 +476,11 @@ gen_random_uuid(PG_FUNCTION_ARGS)
  * The returned timestamp is ensured to be at least SUBMS_MINIMAL_STEP greater
  * than the previous returned timestamp (on this backend).
  */
-static inline int64
+static inline uint64
 get_real_time_ns_ascending()
 {
-	static int64 previous_ns = 0;
-	int64		ns;
+	static uint64 previous_ns = 0;
+	uint64		ns;
 
 	/* Get the current real timestamp */
 
@@ -527,13 +527,13 @@ get_real_time_ns_ascending()
  * used for time-dependent bits of UUID.
  */
 static pg_uuid_t *
-generate_uuidv7(int64 ns)
+generate_uuidv7(uint64 ms, uint64 ns_in_ms)
 {
 	pg_uuid_t  *uuid = palloc(UUID_LEN);
 	int64		unix_ts_ms;
 	int32		increased_clock_precision;
 
-	unix_ts_ms = ns / NS_PER_MS;
+	unix_ts_ms = ms;
 
 	/* Fill in time part */
 	uuid->data[0] = (unsigned char) (unix_ts_ms >> 40);
@@ -547,7 +547,7 @@ generate_uuidv7(int64 ns)
 	 * sub-millisecond timestamp fraction (SUBMS_BITS bits, not
 	 * SUBMS_MINIMAL_STEP_BITS)
 	 */
-	increased_clock_precision = ((ns % NS_PER_MS) * (1 << SUBMS_BITS)) / NS_PER_MS;
+	increased_clock_precision = ((ns_in_ms) * (1 << SUBMS_BITS)) / NS_PER_MS;
 
 	/* Fill the increased clock precision to "rand_a" bits */
 	uuid->data[6] = (unsigned char) (increased_clock_precision >> 8);
@@ -586,7 +586,8 @@ generate_uuidv7(int64 ns)
 Datum
 uuidv7(PG_FUNCTION_ARGS)
 {
-	pg_uuid_t  *uuid = generate_uuidv7(get_real_time_ns_ascending());
+	uint64		ns = get_real_time_ns_ascending();
+	pg_uuid_t  *uuid = generate_uuidv7(ns / NS_PER_MS, ns % NS_PER_MS);
 
 	PG_RETURN_UUID_P(uuid);
 }
@@ -600,7 +601,9 @@ uuidv7_interval(PG_FUNCTION_ARGS)
 	Interval   *shift = PG_GETARG_INTERVAL_P(0);
 	TimestampTz ts;
 	pg_uuid_t  *uuid;
-	int64		ns = get_real_time_ns_ascending();
+	/* 64 bits is enough for real time, but not for a time range of UUID */
+	uint64		ns = get_real_time_ns_ascending();
+	uint64		us;
 
 	/*
 	 * Shift the current timestamp by the given interval. To calculate time
@@ -621,11 +624,10 @@ uuidv7_interval(PG_FUNCTION_ARGS)
 	/*
 	 * Convert a TimestampTz value back to an UNIX epoch and back nanoseconds.
 	 */
-	ns = (ts + (POSTGRES_EPOCH_JDATE - UNIX_EPOCH_JDATE) * SECS_PER_DAY * USECS_PER_SEC)
-		* NS_PER_US + ns % NS_PER_US;
+	us = (ts + (POSTGRES_EPOCH_JDATE - UNIX_EPOCH_JDATE) * SECS_PER_DAY * USECS_PER_SEC);
 
 	/* Generate an UUIDv7 */
-	uuid = generate_uuidv7(ns);
+	uuid = generate_uuidv7(us / 1000, (us % 1000) * 1000 + ns % NS_PER_US);
 
 	PG_RETURN_UUID_P(uuid);
 }
-- 
2.42.0