Function ATRewriteCatalogs

src/backend/commands/tablecmds.c:5969–6039

* ATRewriteCatalogs * * Traffic cop for ALTER TABLE Phase 2 operations. Subcommands are * dispatched in a "safe" execution order (designed to avoid unnecessary * conflicts). */

 * conflicts).
 */
static void
ATRewriteCatalogs(List **wqueue, LOCKMODE lockmode,
				  AlterTableUtilityContext *context)
{
	int			pass;
	ListCell   *ltab;

	/*
	 * We process all the tables "in parallel", one pass at a time.  This is
	 * needed because we may have to propagate work from one table to another
	 * (specifically, ALTER TYPE on a foreign key's PK has to dispatch the
	 * re-adding of the foreign key constraint to the other table).  Work can
	 * only be propagated into later passes, however.
	 */
	for (pass = 0; pass < AT_NUM_PASSES; pass++)
	{
		/* Go through each table that needs to be processed */
		foreach(ltab, *wqueue)
		{
			AlteredTableInfo *tab = (AlteredTableInfo *) lfirst(ltab);
			List	   *subcmds = tab->subcmds[pass];
			ListCell   *lcmd;

			if (subcmds == NIL)
				continue;

			/*
			 * Open the relation and store it in tab.  This allows subroutines
			 * close and reopen, if necessary.  Appropriate lock was obtained
			 * by phase 1, needn't get it again.
			 */
			tab->rel = relation_open(tab->relid, NoLock);

			foreach(lcmd, subcmds)
				ATExecCmd(wqueue, tab,
						  castNode(AlterTableCmd, lfirst(lcmd)),
						  lockmode, pass, context);

			/*
			 * After the ALTER TYPE pass, do cleanup work (this is not done in
			 * ATExecAlterColumnType since it should be done only once if
			 * multiple columns of a table are altered).
			 */
			if (pass == AT_PASS_ALTER_TYPE)
				ATPostAlterTypeCleanup(wqueue, tab, lockmode, context);

			if (tab->rel)
			{
				relation_close(tab->rel, NoLock);
				tab->rel = NULL;
			}
		}
	}

	/* Check to see if a toast table must be added. */
	foreach(ltab, *wqueue)
	{
		AlteredTableInfo *tab = (AlteredTableInfo *) lfirst(ltab);