1) find invalid objects
select owner,object_name,object_type,status from dba_objects where STATUS='INVALID';
2) compile all objects of the database
@$ORACLE_HOME/rdbms/admin/utlrp.sql
3) Compile objects of a schema
-- Compile a view:
alter view schema_name.view_name compile;
-- Compile a function:
alter function schema_name.function_name compile;
-- Compile a procedure:
alter procedure schema_name.procedure_name compile;
-- Compile a package;
alter package schema_name.package_name compile;
alter package schema_name.package_name compile body;