v1-0004-Add-pg_clobber_current_snapshot_timestamp.patch

From ed965c21b4e5841a4afc249f6365b774440ac8cf Mon Sep 17 00:00:00 2001
From: Thomas Munro <thomas.munro@gmail.com>
Date: Fri, 17 Apr 2020 14:10:35 +1200
Subject: [PATCH v1 4/5] Add pg_clobber_current_snapshot_timestamp().

---
 contrib/old_snapshot/old_snapshot--1.0.sql |  5 +++++
 contrib/old_snapshot/time_mapping.c        | 13 +++++++++++++
 2 files changed, 18 insertions(+)

diff --git a/contrib/old_snapshot/old_snapshot--1.0.sql b/contrib/old_snapshot/old_snapshot--1.0.sql
index 9ebb8829e3..aacf1704b5 100644
--- a/contrib/old_snapshot/old_snapshot--1.0.sql
+++ b/contrib/old_snapshot/old_snapshot--1.0.sql
@@ -11,4 +11,9 @@ RETURNS SETOF record
 AS 'MODULE_PATHNAME', 'pg_old_snapshot_time_mapping'
 LANGUAGE C STRICT;
 
+CREATE FUNCTION pg_clobber_current_snapshot_timestamp(now timestamptz)
+RETURNS VOID
+AS 'MODULE_PATHNAME', 'pg_clobber_current_snapshot_timestamp'
+LANGUAGE C STRICT;
+
 -- XXX. Do we want REVOKE commands here?
diff --git a/contrib/old_snapshot/time_mapping.c b/contrib/old_snapshot/time_mapping.c
index 37e0055a00..8728c4ddb5 100644
--- a/contrib/old_snapshot/time_mapping.c
+++ b/contrib/old_snapshot/time_mapping.c
@@ -36,6 +36,7 @@ typedef struct
 
 PG_MODULE_MAGIC;
 PG_FUNCTION_INFO_V1(pg_old_snapshot_time_mapping);
+PG_FUNCTION_INFO_V1(pg_clobber_current_snapshot_timestamp);
 
 static OldSnapshotTimeMapping *GetOldSnapshotTimeMapping(void);
 static TupleDesc MakeOldSnapshotTimeMappingTupleDesc(void);
@@ -157,3 +158,15 @@ MakeOldSnapshotTimeMappingTuple(TupleDesc tupdesc, OldSnapshotTimeMapping *mappi
 
 	return heap_form_tuple(tupdesc, values, nulls);
 }
+
+Datum
+pg_clobber_current_snapshot_timestamp(PG_FUNCTION_ARGS)
+{
+	TimestampTz new_current_timestamp = PG_GETARG_TIMESTAMPTZ(0);
+
+	LWLockAcquire(OldSnapshotTimeMapLock, LW_EXCLUSIVE);
+	oldSnapshotControl->current_timestamp = new_current_timestamp;
+	LWLockRelease(OldSnapshotTimeMapLock);
+
+	PG_RETURN_NULL();
+}
-- 
2.20.1