> How many records approx.?

one hours a go i just do an select count(*) from session but still now answer so i thing a lot ...

> By using isc_tpb_no_rec_version you basically disable Firebird's MVCC
> capabilities, so you explicitly tell Firebird to not use the back-record
> version mechansim when changing/deleting data. This beams you back into
> the good old days of MS SQL Server 2000 in read/write scenarios. ;-)

so in this way what could be the most suitable isolation level ?

> Additionally, you also might take garbage collection into account for
> both, record data and index entries.
>
> You may inspect MON$RECORD_STATS for getting some counters on if garbage
> collection is performed. The Trace API gives you that information per
> executed statement as well ...

yes, but days just to do the garbage :(
for now i still waiting that my query return an i will after query also the MON$RECORD_STATS to see ...