Fill tuple before HeapSatisfiesHOTAndKeyUpdate

Failing to do this results in almost all updates to system catalogs
being non-HOT updates, because the OID column would differ (not having
been set for the new tuple), which is an indexed column.

While at it, make sure to set the tableoid early in both old and new
tuples as well.  This isn't of much consequence, since that column is
seldom (never?) indexed.

Report and patch from Andres Freund.

src/backend/access/heap/heapam.c

@@ -2978,10 +2978,33 @@ heap_update(Relation relation, ItemPointer otid, HeapTuple newtup,
 	lp = PageGetItemId(page, ItemPointerGetOffsetNumber(otid));
 	Assert(ItemIdIsNormal(lp));
 
+	/*
+	 * Fill in enough data in oldtup for HeapSatisfiesHOTandKeyUpdate to work
+	 * properly.
+	 */
+	oldtup.t_tableOid = RelationGetRelid(relation);
 	oldtup.t_data = (HeapTupleHeader) PageGetItem(page, lp);
 	oldtup.t_len = ItemIdGetLength(lp);
 	oldtup.t_self = *otid;
 
+	/* the new tuple is ready, except for this: */
+	newtup->t_tableOid = RelationGetRelid(relation);
+
+	/* Fill in OID for newtup */
+	if (relation->rd_rel->relhasoids)
+	{
+#ifdef NOT_USED
+		/* this is redundant with an Assert in HeapTupleSetOid */
+		Assert(newtup->t_data->t_infomask & HEAP_HASOID);
+#endif
+		HeapTupleSetOid(newtup, HeapTupleGetOid(&oldtup));
+	}
+	else
+	{
+		/* check there is not space for an OID */
+		Assert(!(newtup->t_data->t_infomask & HEAP_HASOID));
+	}
+
 	/*
 	 * If we're not updating any "key" column, we can grab a weaker lock type.
 	 * This allows for more concurrency when we are running simultaneously with
@@ -3243,20 +3266,7 @@ l2:
 	 */
 	CheckForSerializableConflictIn(relation, &oldtup, buffer);
 
-	/* Fill in OID and transaction status data for newtup */
-	if (relation->rd_rel->relhasoids)
-	{
-#ifdef NOT_USED
-		/* this is redundant with an Assert in HeapTupleSetOid */
-		Assert(newtup->t_data->t_infomask & HEAP_HASOID);
-#endif
-		HeapTupleSetOid(newtup, HeapTupleGetOid(&oldtup));
-	}
-	else
-	{
-		/* check there is not space for an OID */
-		Assert(!(newtup->t_data->t_infomask & HEAP_HASOID));
-	}
+	/* Fill in transaction status data */
 
 	/*
 	 * If the tuple we're updating is locked, we need to preserve the locking
@@ -3318,7 +3328,6 @@ l2:
 	newtup->t_data->t_infomask |= HEAP_UPDATED | infomask_new_tuple;
 	newtup->t_data->t_infomask2 |= infomask2_new_tuple;
 	HeapTupleHeaderSetXmax(newtup->t_data, xmax_new_tuple);
-	newtup->t_tableOid = RelationGetRelid(relation);
 
 	/*
 	 * Replace cid with a combo cid if necessary.  Note that we already put