There is a flag in the MyISAM file that indicates whether or not the table was closed correctly. This will soon be used for automatic repair in the MySQL server. Dynamic size rows will now be much less fragmented when mixing deletes with updates and inserts. This is done by automatically combining adjacent deleted blocks and by extending blocks if the next block is deleted. MyISAM also supports the following things, which MySQL will be able to use in the near future.
All key segments have their own language definition.
This will enable MySQL to have different language definitions per column. String indexes are space compressed. If the first index part is a string, it will also be prefix compressed. Prefix compression is used on keys that start with a string. Prefix compression helps if there are many strings with an identical prefix.