Hi Tom,

i looked into this , it seems like valgrind catches the uninitialised padding bytes, which
repack worker is writing using BufFileWrite, it seems this fix solved the problem.

diff --git a/src/backend/utils/time/snapmgr.c b/src/backend/utils/time/snapmgr.c
index 2e6197f5f35..f5682b87626 100644
--- a/src/backend/utils/time/snapmgr.c
+++ b/src/backend/utils/time/snapmgr.c
@@ -1739,6 +1739,8 @@ SerializeSnapshot(Snapshot snapshot, char *start_address)
 
  Assert(snapshot->subxcnt >= 0);
 
+ MemSet(&serialized_snapshot, 0, sizeof(SerializedSnapshotData));
+
  /* Copy all required fields */
  serialized_snapshot.xmin = snapshot->xmin;
  serialized_snapshot.xmax = snapshot->xmax;

thoughts?