Function check_selective_binary_conversion

contrib/file_fdw/file_fdw.c:866–981

* check_selective_binary_conversion * * Check to see if it's useful to convert only a subset of the file's columns * to binary. If so, construct a list of the column names to be converted, * return that at *columns, and return true. (Note that it's possible to * determine that no columns need be converted, for instance with a COUNT(*) * query. So we can't use returning a NIL list to indic

 * query.  So we can't use returning a NIL list to indicate failure.)
 */
static bool
check_selective_binary_conversion(RelOptInfo *baserel,
								  Oid foreigntableid,
								  List **columns)
{
	ForeignTable *table;
	ListCell   *lc;
	Relation	rel;
	TupleDesc	tupleDesc;
	AttrNumber	attnum;
	Bitmapset  *attrs_used = NULL;
	bool		has_wholerow = false;
	int			numattrs;
	int			i;

	*columns = NIL;				/* default result */

	/*
	 * Check format of the file.  If binary format, this is irrelevant.
	 */
	table = GetForeignTable(foreigntableid);
	foreach(lc, table->options)
	{
		DefElem    *def = (DefElem *) lfirst(lc);

		if (strcmp(def->defname, "format") == 0)
		{
			char	   *format = defGetString(def);

			if (strcmp(format, "binary") == 0)
				return false;
			break;
		}
	}

	/* Collect all the attributes needed for joins or final output. */
	pull_varattnos((Node *) baserel->reltarget->exprs, baserel->relid,
				   &attrs_used);

	/* Add all the attributes used by restriction clauses. */
	foreach(lc, baserel->baserestrictinfo)
	{
		RestrictInfo *rinfo = (RestrictInfo *) lfirst(lc);

		pull_varattnos((Node *) rinfo->clause, baserel->relid,
					   &attrs_used);
	}

	/* Convert attribute numbers to column names. */
	rel = table_open(foreigntableid, AccessShareLock);
	tupleDesc = RelationGetDescr(rel);

	while ((attnum = bms_first_member(attrs_used)) >= 0)
	{
		/* Adjust for system attributes. */
		attnum += FirstLowInvalidHeapAttributeNumber;

		if (attnum == 0)