IDS 9.21
Linux 7.3

I have a table with 4 000 000 rows.
This table change very often(5 rows per second).
This table has bad indexes. How can I recreate indexes on modifying table.
Clients must work with this table during creating indexes.

Unfortunately you need exclusive access to a table to create an index. So no-one can even be selecting from the table when you create the indexes. You would really have to schedule some down time, and then do your index work.