Not much. The obligatory info() method—although we cannot do much here, we do not even know the number of rows in the table. Let's just return something—MySQL will not take this value too seriously, because we do not have the HA_STATS_RECORDS_IS_EXACT flag in table_flags():
int ha_html::info(uint flag)
{
if (flag & HA_STATUS_VARIABLE)
stats.records = 10;
return 0;
}
Then, there is the external_lock() method. It is an important method—with a few exceptions MySQL calls it at the beginning and at the end of every statement. The name is historical, MyISAM and pre-MyISAM engines stored tables in files—just like our engine does—but used file locking to prevent multiple processes from modifying the same table file in parallel. The method "external lock" was designed to allow the engine to take this (external for MySQL) lock, after MySQL has taken its own "internal" table lock. The second argument of external_lock() is either F_UNLCK (at the end of the statement) or F_RDLCK...