Index and data table growing

[Ludovic Maillet]

Hello

My problem:

I'm using a database as a 'shared' and real time storage: a soft is writing while another soft is deleting some rows periodicaly while a third soft is reading some lines.
The database is never containing a lot a rows, but the rate of writing/deleting/reading is very high (300/sec)
After a moment, even if my database is empty, the index and data stay very large and the query time becomes very long.
For example, a SELECT COUNT(*) display 0 after .... 40 secs !!!

I found a solution to clean index and data entries and then improve performance: DELETE FROM myTable... but it is not a good solution because my database is keeping data in a real time traffic and will never be empty for a long time.

Solution ?

Does a configuration exist to limit index/data table, or to optimize, or.. ? ... without having to lock/block access to the table during a long time ???

Thanks
Ludovic Maillet