DBW0 process in the V$lock

Good Morning Friends,
In my production server when I used to query the the view V$LOCK, I used to get some records(locks) and gets released after some time. From 4 days time, I am seeing nearly 90 records in the V$LOCK for the SID=2, this SID is of the back ground process DBW0(DB Writer). Why this is happening? Can any one let me know in which cases this will happen. Please throw some light on this. This is first time I am seeing this kind of scenario from 1 year after my production server is live.
Thanks in Advance
V6163