> even philipe in some past time suggest us to go in some NoSQL database ! cold in the back when we know who is phillipe :(

Again Stephane, please be carefull when you read and write post
I said that for some part of your application a solution NoSQL can be
a solution, not to change completly from Firebird to a NoSQL solution
I also said that perhaps you have to change in some way how your data
are structured, perhaps some table have to be change or new table
created, like it is often need for OLTP , ...

did you try for example to make working together Memcached and Firebird ?

and more, you come here with problems, but never we have a complete
see of your architecture and how you choosed fulfill your needs, so
each time, we are giving partial answers. May be it is also time for
you to put all on the table a think globally to your software
architecture, certainly also with the help of outside look.

RDBMS are often matter of balanced choice, for example, the fact that
you have so much indexes is certainly good for some point, but also
bad for others etc ...