bad performance

Hi,
    I have an application that has an HASH db where I make a lot of data
update for each record.
Performance seems to be pretty good, but all the update seems to be reported
just in memory.
When I use the sync method after each update to synchronize them to the
file, the db became very slow (twice than gdbm).

There is another faster method to ensure that record are updated on file ?

Thanks,
Giambattista Bloisi