Function ATRewriteTable

src/backend/commands/tablecmds.c:7369–7745

* ATRewriteTable: scan or rewrite one table * * OIDNewHeap is InvalidOid if we don't need to rewrite */

 * OIDNewHeap is InvalidOid if we don't need to rewrite
 */
static void
ATRewriteTable(AlteredTableInfo *tab, Oid OIDNewHeap, LOCKMODE lockmode)
{
	Relation	oldrel;
	Relation	newrel;
	TupleDesc	oldTupDesc;
	TupleDesc	newTupDesc;
	bool		needscan = false;
	List	   *notnull_attrs;
	int			i;
	ListCell   *l;
	EState	   *estate;
	CommandId	mycid;
	BulkInsertState bistate;
	int			ti_options;
	ExprState  *partqualstate = NULL;

	/*
	 * Open the relation(s).  We have surely already locked the existing
	 * table.
	 */
	oldrel = table_open(tab->relid, NoLock);
	oldTupDesc = tab->oldDesc;
	newTupDesc = RelationGetDescr(oldrel);	/* includes all mods */

	if (OidIsValid(OIDNewHeap))
		newrel = table_open(OIDNewHeap, lockmode);
	else
		newrel = NULL;

	/*
	 * Prepare a BulkInsertState and options for table_tuple_insert. Because
	 * we're building a new heap, we can skip WAL-logging and fsync it to disk
	 * at the end instead (unless WAL-logging is required for archiving or
	 * streaming replication). The FSM is empty too, so don't bother using it.
	 */
	if (newrel)
	{
		mycid = GetCurrentCommandId(true);
		bistate = GetBulkInsertState();
		ti_options = TABLE_INSERT_SKIP_FSM;
	}
	else
	{
		/* keep compiler quiet about using these uninitialized */
		mycid = 0;
		bistate = NULL;
		ti_options = 0;
	}

	/*
	 * Generate the constraint and default execution states
	 */

	estate = CreateExecutorState();

	/* Build the needed expression execution states */
	foreach(l, tab->constraints)