v2-0001-UUDv7-fix-offset-computations-in-dates-after-2262.patch

From 6890f52395a924f6af33eb86c2c3addb204ef483 Mon Sep 17 00:00:00 2001
From: Andrey Borodin <amborodin@acm.org>
Date: Fri, 31 Jan 2025 12:03:16 +0500
Subject: [PATCH v2] 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 | 22 ++++++++++++----------
 1 file changed, 12 insertions(+), 10 deletions(-)

diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c
index 4f8402ef92..f579bb3a64 100644
--- a/src/backend/utils/adt/uuid.c
+++ b/src/backend/utils/adt/uuid.c
@@ -28,6 +28,7 @@
 /* helper macros */
 #define NS_PER_S	INT64CONST(1000000000)
 #define NS_PER_MS	INT64CONST(1000000)
+#define US_PER_MS	INT64CONST(1000)
 #define NS_PER_US	INT64CONST(1000)
 
 /*
@@ -69,6 +70,7 @@ 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 pg_uuid_t *generate_uuidv7(uint64 unix_ts_ms, uint32 ns_in_ms);
 
 Datum
 uuid_in(PG_FUNCTION_ARGS)
@@ -523,18 +525,16 @@ get_real_time_ns_ascending()
  * described in the RFC. This method utilizes 12 bits from the "rand_a" bits
  * to store a 1/4096 (or 2^12) fraction of sub-millisecond precision.
  *
- * ns is a number of nanoseconds since start of the UNIX epoch. This value is
+ * unix_ts_ms is a number of milliseconds since start of the UNIX epoch,
+ * ns_in_ms is a number of nanoseconds within millisecond. These values are
  * used for time-dependent bits of UUID.
  */
 static pg_uuid_t *
-generate_uuidv7(int64 ns)
+generate_uuidv7(uint64 unix_ts_ms, uint32 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;
-
 	/* Fill in time part */
 	uuid->data[0] = (unsigned char) (unix_ts_ms >> 40);
 	uuid->data[1] = (unsigned char) (unix_ts_ms >> 32);
@@ -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());
+	int64		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;
+	/* 64 bits is enough for real time, but not for a time range of UUID */
 	int64		ns = get_real_time_ns_ascending();
+	int64		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 / US_PER_MS, (us % US_PER_MS) * NS_PER_US + ns % NS_PER_US);
 
 	PG_RETURN_UUID_P(uuid);
 }
-- 
2.39.5 (Apple Git-154)