SQL & PL/SQL

All,

I wrote query as below which is having quite high disk usage. I believe this to be reason for slow performance of my code (Although bad on performance tuning, but based on what I read on blogs that disk reads should be less). Any suggestion/help of how can this be performed fast.

SELECT DECODE (MSSO.SOURCE_TYPE, 1, 'T', 2, 'M', 3, 'B') SOURCE_TYPE ,
MSSO.RANK ,MSSO.ALLOCATION_PERCENT ,MSSO.VENDOR_ID ,MSSO.VENDOR_SITE_ID ,
MSSO.SOURCE_ORGANIZATION_ID ,TO_CHAR (MSRO.EFFECTIVE_DATE, 'RRRR/MM/DD')
ACTIVE_DATE ,TO_CHAR (MSRO.DISABLE_DATE, 'RRRR/MM/DD') END_DATE
FROM
MRP_SOURCING_RULES MSR ,MRP_SR_RECEIPT_ORG MSRO ,MRP_SR_SOURCE_ORG MSSO
WHERE MSR.SOURCING_RULE_ID = MSRO.SOURCING_RULE_ID AND MSSO.SR_RECEIPT_ID =
MSRO.SR_RECEIPT_ID AND MSR.SOURCING_RULE_ID = :B1 AND MSSO.RANK = (SELECT
MIN (RANK) FROM MRP_SR_SOURCE_ORG MSSO1 WHERE MSSO.SR_RECEIPT_ID =
MSSO1.SR_RECEIPT_ID) AND TRUNC (NVL (MSRO.EFFECTIVE_DATE, SYSDATE)) <=
TRUNC (SYSDATE) AND TRUNC (NVL (MSRO.DISABLE_DATE, SYSDATE)) >= TRUNC
(SYSDATE) AND ( EXISTS ( SELECT 1 FROM HR_ORGANIZATION_INFORMATION OOD ,
PO_VENDOR_SITES_ALL S WHERE OOD.ORGANIZATION_ID = :B2 AND
OOD.ORG_INFORMATION3 = S.ORG_ID AND OOD.ORG_INFORMATION_CONTEXT =
'Accounting Information' AND S.VENDOR_SITE_ID = MSSO.VENDOR_SITE_ID) OR
MSSO.VENDOR_SITE_ID IS NULL OR MSSO.SOURCE_TYPE <>3)




call count cpu elapsed disk query current rows
------- ------ -------- ---------- ---------- ---------- ---------- ----------
Parse 1 0.00 0.00 0 0 0 0
Execute 89400 23.16 23.35 0 0 0 0
Fetch 89400 69.28 86.57 1338 1740766 0 88732
------- ------ -------- ---------- ---------- ---------- ---------- ----------
total 178801 92.44 109.93 1338 1740766 0 88732





Thanks
Sachin