跨DBLINK Insert into慢的问题解决
一、问题描述
今天用户给出一个SQL，select执行很快，但是insert进表时就很慢，半天没个动静。
SQL执行用时：310s
INSERT INTO uop_sta_cen.WXL_IDC_STATE
(INS_DATE, DOMAIN_ID, EPARCHY_CODE, CUST_ID, USER_ID, SERIAL_NUMBER)
SELECT SYSDATE,
'3',
EPARCHY_CODE,
to_char(CUST_ID),
to_char(USER_ID),
SERIAL_NUMBER
FROM UCR_CRM3.TF_F_USER@UQRY_SEL_TO_HACRMDB22 T
WHERE T.REMOVE_TAG = '0'
AND T.USER_ID IN
(SELECT A.USER_ID
FROM UCR_CRM3.TF_F_USER_SVC@UQRY_SEL_TO_HACRMDB22 A
WHERE A.SERVICE_ID IN ('46000003', '46000005', '46000006')
AND SYSDATE BETWEEN A.START_DATE AND A.END_DATE);
单独执行SELECT,用时0.078s
SELECT SYSDATE,
'3',
EPARCHY_CODE,
to_char(CUST_ID),
to_char(USER_ID),
SERIAL_NUMBER
FROM UCR_CRM3.TF_F_USER@UQRY_SEL_TO_HACRMDB22 T
WHERE T.REMOVE_TAG = '0'
AND T.USER_ID IN
(SELECT A.USER_ID
FROM UCR_CRM3.TF_F_USER_SVC@UQRY_SEL_TO_HACRMDB22 A
WHERE A.SERVICE_ID IN ('46000003', '46000005', '46000006')
AND SYSDATE BETWEEN A.START_DATE AND A.END_DATE)
二、原因分析
从上面执行计划，可以看出，连接方式有变化，Nested loops-->Hash join，这就是慢的原因。
不用DBLINK，直接本地INSERT很快，也是使用NL的方式。
三、问题解决
可用两种方法解决：
-
不用跨DBLINK，直接本地INSERT,再通过DBLINK读取即可;
-
使用hint方式，强制使用NL连接。
INSERT INTO uop_sta_cen.WXL_IDC_STATE
(INS_DATE, DOMAIN_ID, EPARCHY_CODE, CUST_ID, USER_ID, SERIAL_NUMBER)
SELECT /*+ use_nl(A,T)*/ SYSDATE,
'3',
T.EPARCHY_CODE,
to_char(T.CUST_ID),
to_char(T.USER_ID),
SERIAL_NUMBER
FROM UCR_CRM3.TF_F_USER@DBLNK_NGCRM2 T,(SELECT distinct USER_ID
FROM UCR_CRM3.TF_F_USER_SVC@DBLNK_NGCRM2
WHERE SERVICE_ID IN ('46000003', '46000005', '46000006')
AND SYSDATE BETWEEN START_DATE AND END_DATE) A
WHERE T.REMOVE_TAG = '0'
AND T.USER_ID =A.user_id
用时 0.109S
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转载于:http://blog.itpub.net/7836221/viewspace-2213282/