Is it necessary flush data of buffer for booking seats?

[Francisco Carlos]

I am building a FBNTester for test my application
by simulating several clients accessing DataServer server.
The mechanism of lock and unlock seems are right, but I note that suncertify.db.modify() dont flush
buffer immediatly.
In my test, i have a client that read the available seats number.. and i had a surprise when
i observe that the available seats number read by that client wasn�t incorret??? I think that each a of that clients (A, B, C, etc) read the record of db.db and store in a buffer.
For example:
client A read 120 seats of flight X
client A booking 2 seats
client B read 120 seats of fligh X
client A booking 2 seats
The JVM stores 118 left seats.
The right would be 116 lefts seats.
The clients A, B, etc call the bookSeats() method
of DataAccessFacade.
I implemented a DataAccessFacade class that a method bookSeats. That method call the methods modify(), lock() and unlock().
Some sugestion???
Francisco Carlos