Hi DBA's

I have 3 queries.

1. How will you find at the end of the day which are the expensive queries??
How will I find that??

2. Suppose Instance is crashed due to Shutdown Abort .. How Oracle will come to know at next startup
that it need Instance Recovery??

3. Suppose I have installed Unix on server and I am planning to Install Oracle on server??
what will be my major responsibilities/decisions as a DBA before installation of Oracle??


Regards,

Paresh