Function BuildHardcodedDescriptor

src/backend/utils/cache/relcache.c:4546–4574

* GetPgClassDescriptor -- get a predefined tuple descriptor for pg_class * GetPgIndexDescriptor -- get a predefined tuple descriptor for pg_index * * We need this kluge because we have to be able to access non-fixed-width * fields of pg_class and pg_index before we have the standard catalog caches * available. We use predefined data that's set up in just the same way as * the bootstrapped r

 * extracting fields.
 */
static TupleDesc
BuildHardcodedDescriptor(int natts, const FormData_pg_attribute *attrs)
{
	TupleDesc	result;
	MemoryContext oldcxt;
	int			i;

	oldcxt = MemoryContextSwitchTo(CacheMemoryContext);

	result = CreateTemplateTupleDesc(natts);
	result->tdtypeid = RECORDOID;	/* not right, but we don't care */
	result->tdtypmod = -1;

	for (i = 0; i < natts; i++)
	{
		memcpy(TupleDescAttr(result, i), &attrs[i], ATTRIBUTE_FIXED_PART_SIZE);
		/* make sure attcacheoff is valid */
		TupleDescAttr(result, i)->attcacheoff = -1;
	}

	/* initialize first attribute's attcacheoff, cf RelationBuildTupleDesc */
	TupleDescAttr(result, 0)->attcacheoff = 0;

	/* Note: we don't bother to set up a TupleConstr entry */

	MemoryContextSwitchTo(oldcxt);

	return result;
}

static TupleDesc
GetPgClassDescriptor(void)