HOW PL/SQL GETS EXECUTED

http://comsci.liu.edu/~vasilaky/db2/lec1.htm

the PL/SQL engine on the server where it is compiled. The named PL/SQL
block is compiled only at the time of its creation, or if it has been
changed. The compilation process includes syntax checking, binding,
and p-code generation.

Oracle guarantees a read-consistent view
of the data. Until that point, all data that has been inserted or updated
will be held in memory and only be available to the current user. The
rows that have been changed will be locked by the current user and will
not be available for updating to other users until the locks have been re-leased.