Function ATExecSetOptions

src/backend/commands/tablecmds.c:10000–10071

* Return value is the address of the modified column */

 * Return value is the address of the modified column
 */
static ObjectAddress
ATExecSetOptions(Relation rel, const char *colName, Node *options,
				 bool isReset, LOCKMODE lockmode)
{
	Relation	attrelation;
	HeapTuple	tuple,
				newtuple;
	Form_pg_attribute attrtuple;
	AttrNumber	attnum;
	Datum		datum,
				newOptions;
	bool		isnull;
	ObjectAddress address;
	Datum		repl_val[Natts_pg_attribute];
	bool		repl_null[Natts_pg_attribute];
	bool		repl_repl[Natts_pg_attribute];

	attrelation = table_open(AttributeRelationId, RowExclusiveLock);

	tuple = SearchSysCacheAttName(RelationGetRelid(rel), colName);

	if (!HeapTupleIsValid(tuple))
		ereport(ERROR,
				(errcode(ERRCODE_UNDEFINED_COLUMN),
				 errmsg("column \"%s\" of relation \"%s\" does not exist",
						colName, RelationGetRelationName(rel))));
	attrtuple = (Form_pg_attribute) GETSTRUCT(tuple);

	attnum = attrtuple->attnum;
	if (attnum <= 0)
		ereport(ERROR,
				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
				 errmsg("cannot alter system column \"%s\"",
						colName)));

	/* Generate new proposed attoptions (text array) */
	datum = SysCacheGetAttr(ATTNAME, tuple, Anum_pg_attribute_attoptions,
							&isnull);
	newOptions = transformRelOptions(isnull ? (Datum) 0 : datum,
									 castNode(List, options), NULL, NULL,
									 false, isReset);
	/* Validate new options */
	(void) attribute_reloptions(newOptions, true);

	/* Build new tuple. */
	memset(repl_null, false, sizeof(repl_null));
	memset(repl_repl, false, sizeof(repl_repl));
	if (newOptions != (Datum) 0)
		repl_val[Anum_pg_attribute_attoptions - 1] = newOptions;
	else
		repl_null[Anum_pg_attribute_attoptions - 1] = true;
	repl_repl[Anum_pg_attribute_attoptions - 1] = true;
	newtuple = heap_modify_tuple(tuple, RelationGetDescr(attrelation),
								 repl_val, repl_null, repl_repl);

	/* Update system catalog. */
	CatalogTupleUpdate(attrelation, &newtuple->t_self, newtuple);