Function EXT_cardinality

src/jrd/ext.cpp:161–217

double EXT_cardinality(thread_db* tdbb, jrd_rel* relation)
{
/**************************************
 *
 *	E X T _ c a r d i n a l i t y
 *
 **************************************
 *
 * Functional description
 *	Return cardinality for the external file.
 *
 **************************************/
	ExternalFile* const file = relation->rel_file;
	fb_assert(file);

	try
	{
		bool must_close = false;
		if (!file->ext_ifi)
		{
			ext_fopen(tdbb->getDatabase(), file);
			must_close = true;
		}

		FB_UINT64 file_size = 0;

#ifdef WIN_NT
		struct __stat64 statistics;
		if (!_fstat64(_fileno(file->ext_ifi), &statistics))
#else
		struct STAT statistics;
		if (!os_utils::fstat(fileno(file->ext_ifi), &statistics))
#endif
		{
			file_size = statistics.st_size;
		}

		if (must_close)
		{
			fclose(file->ext_ifi);
			file->ext_ifi = NULL;
		}

		const Format* const format = MET_current(tdbb, relation);
		fb_assert(format && format->fmt_length);
		const USHORT offset = (USHORT)(IPTR) format->fmt_desc[0].dsc_address;
		const ULONG record_length = format->fmt_length - offset;

		return (double) file_size / record_length;
	}
	catch (const Exception&)
	{
		fb_utils::init_status(tdbb->tdbb_status_vector);
	}

	return 10000; // just a wild guess
}