I'm trying to use logminer tool but I'm encountering some problems.

1) Sometimes it caused an error while I'm querying v$logmnr_contents and then it won't work until I restart the database. Have you ever had this problem? Is it frequent?
Is there a known way to fix it?

2) I'm trying to create a specific user dedicated to the analyse of log but haven't succeed yet. It seems there's a problem of rights as the scripts are owned by sys.
When I try to add a logfile to analyze I got this error :
"dbms_logmnr.NEW identifier undeclared"
Which rights should I give to this user in order to make it work?

3) Can we access the LGWR trace file?

4) In Oracle Documentation, it's said that queries that haven't been commited yet may be added to the redo log files. That means Oracle has a way to know that they haven't been commited in order to rollback them if needed. Do you know how?