1. Monitor Shared Pool Information:
select to_number(value) shared_pool_size, sum_obj_size, sum_sql_size, sum_user_size,
(sum_obj_size + sum_sql_size+sum_user_size)* 1.3 min_shared_pool
  from (select sum(sharable_mem) sum_obj_size
  from v$db_object_cache where type <> 'CURSOR'),
(select sum(sharable_mem) sum_sql_size from v$sqlarea),
(select sum(250 * users_opening) sum_user_size from v$sqlarea), v$parameter
where name = 'shared_pool_size';

2. Monitor SGA Information:
SELECT SUM(VALUE)/1024/1024 "Size in MB" from SYS.v_$sga;
select    NAME,  BYTES from    v$sgastat  order by NAME;

3. Monitor PGA Information:
Select st.sid "SID", sn.name "TYPE", ceil(st.value / 1024 / 1024/1024) "GB"
from v$sesstat st, v$statname sn where st.statistic# = sn.statistic#
and sid in (select sid from v$session where username like UPPER('hrms'))
and upper(sn.name) like '%PGA%' order by st.sid, st.value desc;

4. Monitor CPU Usage Information:
select  ss.username, se.SID, VALUE/100 cpu_usage_seconds
from v$session ss,  v$sesstat se,  v$statname sn where se.STATISTIC# = sn.STATISTIC#
and NAME like '%CPU used by this session%' and se.SID = ss.SID
and  ss.status='ACTIVE' and  ss.username is not null order by VALUE desc;

5. Disk I/O Report:
WITH totreadwrite AS (SELECT SUM (phyrds) phys_reads, SUM (phywrts) phys_wrts FROM v$filestat)
SELECT  NAME, phyrds, phyrds * 100 / trw.phys_reads read_pct,
    phywrts, phywrts * 100 / trw.phys_wrts write_pct
FROM totreadwrite trw, v$datafile df, v$filestat fs
  WHERE df.file# = fs.file# ORDER BY phyrds DESC;

6. IO Usage for a Query:
select b.sql_text "Statement ", a.Disk_reads "Disk Reads", a.executions "Executions",
a.disk_reads/decode(a.executions,0,1,a.executions) "Ratio",c.username
from  v$sqlarea a, v$sqltext_with_newlines b,dba_users c
where  a.parsing_user_id = c.user_id and a.address=b.address and a.disk_reads>100000
order by a.disk_reads desc,b.piece;

7. Monitor Disk I/O Contention:
select  NAME,  PHYRDS "Physical Reads",
    round((PHYRDS / PD.PHYS_READS)*100,2) "Read %",  PHYWRTS "Physical Writes",
    round(PHYWRTS * 100 / PD.PHYS_WRTS,2) "Write %",  fs.PHYBLKRD+FS.PHYBLKWRT "Total Block I/O's" from (    select    sum(PHYRDS) PHYS_READS, sum(PHYWRTS) PHYS_WRTS
    from    v$filestat    ) pd,  v$datafile df,  v$filestat fs
where    df.FILE# = fs.FILE#
order    by fs.PHYBLKRD+fs.PHYBLKWRT desc;