insertion becoming slow

thanks for the help..
i removed a few indexes,
but i cant remove the primary key and uniqye key constraints ..whoch means that indexes will be made on these 2 attributes.

i have four tables, each having such 2 attributes, one which is the primary key and the other is the uniqu key.

and the insertion to these 4 tables is by means of 4 stored procedures (1 for each table).

These stored procedures are being called within a transaction ..which i begin from the application..

i noticed by putting timers that it is the "COMMIT TRANSACTION" statement to the database (after calling the 4 stored procedures) that is taking time.

but commit transaction is not slow each time, in fact it remains very small for a large number of installs ..then suddenly rises (becomes almost 8 times) and then falls again.

why such a behaviour?

thanks
regards
surabhi