An example of logon trigger

By user and by Module:
CREATE OR REPLACE TRIGGER SET_OPTIMIZER_ONLOGIN AFTER LOGON ON DATABASE
DECLARE
uname VARCHAR2(30);
app VARCHAR2(30);
cmmd VARCHAR2(64);
BEGIN
cmmd:='ALTER SESSION SET optimizer_index_cost_adj=20';
uname:=SYS_CONTEXT('USERENV','SESSION_USER');
app := upper(SYS_CONTEXT('USERENV','MODULE'));
IF uname = '*****' and app like 'SQLPLUS.EXE' then
   EXECUTE IMMEDIATE cmmd;
END IF;
EXCEPTION
WHEN OTHERS THEN
NULL;
END;
/

By module only:
CREATE OR REPLACE TRIGGER SET_OPTIMIZER_ONLOGIN AFTER LOGON ON DATABASE
DECLARE
app VARCHAR2(30);
cmmd VARCHAR2(64);
BEGIN
cmmd:='ALTER SESSION SET optimizer_index_cost_adj=20';
app := upper(SYS_CONTEXT('USERENV','MODULE'));
IF app like 'RUNBATCH.EXE' then
   EXECUTE IMMEDIATE cmmd;
END IF;
EXCEPTION
WHEN OTHERS THEN
NULL;
END;
/