Oracle Performance Comparison between VARCHAR and NUMBER

Isolation And Consistency Characteristics of Transaction

Oracle Support only two isolation level.
1.) Repeatable Read
2.) Serializable

http://www.youtube.com/watch?v=phZnuHV13rc
http://en.wikipedia.org/wiki/Isolation_(database_systems)

ROWID vs PRIMARY KEY

http://www.oracle-base.com/articles/misc/rowids-for-plsql-performance.php