GaussDB实际调优案例：增加JOIN列非空条件

现象描述
SELECT
*
FROM
( ( SELECT
STARTTIME STTIME,
SUM(NVL(PAGE_DELAY_MSEL,0)) PAGE_DELAY_MSEL,
SUM(NVL(PAGE_SUCCEED_TIMES,0)) PAGE_SUCCEED_TIMES,
SUM(NVL(FST_PAGE_REQ_NUM,0)) FST_PAGE_REQ_NUM,
SUM(NVL(PAGE_AVG_SIZE,0)) PAGE_AVG_SIZE,
SUM(NVL(FST_PAGE_ACK_NUM,0)) FST_PAGE_ACK_NUM,
SUM(NVL(DATATRANS_DW_DURATION,0)) DATATRANS_DW_DURATION,
SUM(NVL(PAGE_SR_DELAY_MSEL,0)) PAGE_SR_DELAY_MSEL
FROM
PS.SDR_WEB_BSCRNC_1DAY SDR
INNER JOIN (SELECT
BSCRNC_ID,
BSCRNC_NAME,
ACCESS_TYPE,
ACCESS_TYPE_ID
FROM
nethouse.DIM_LOC_BSCRNC
GROUP BY
BSCRNC_ID,
BSCRNC_NAME,
ACCESS_TYPE,
ACCESS_TYPE_ID) DIM
ON SDR.BSCRNC_ID = DIM.BSCRNC_ID
AND DIM.ACCESS_TYPE_ID IN (0,1,2)
INNER JOIN nethouse.DIM_RAT_MAPPING RAT
ON (RAT.RAT = SDR.RAT)
WHERE
( (STARTTIME >= 1461340800
AND STARTTIME < 1461427200) )
AND RAT.ACCESS_TYPE_ID IN (0,1,2)
–and SDR.BSCRNC_ID is not null
GROUP BY
STTIME ) ) ;

执行计划如图1所示。

图1 增加JOIN列非空条件（一）

优化分析
分析执行计划图1可知，在顺序扫描阶段耗时较多。
多表JOIN中，由于表PS.SDR_WEB_BSCRNC_1DAY的JOIN列“BSCRNC_ID”存在大量空值，JOIN性能差。
建议在语句中手动添加JOIN列的非空判断，修改后的语句如下所示。

SELECT
*
FROM
( ( SELECT
STARTTIME STTIME,
SUM(NVL(PAGE_DELAY_MSEL,0)) PAGE_DELAY_MSEL,
SUM(NVL(PAGE_SUCCEED_TIMES,0)) PAGE_SUCCEED_TIMES,
SUM(NVL(FST_PAGE_REQ_NUM,0)) FST_PAGE_REQ_NUM,
SUM(NVL(PAGE_AVG_SIZE,0)) PAGE_AVG_SIZE,
SUM(NVL(FST_PAGE_ACK_NUM,0)) FST_PAGE_ACK_NUM,
SUM(NVL(DATATRANS_DW_DURATION,0)) DATATRANS_DW_DURATION,
SUM(NVL(PAGE_SR_DELAY_MSEL,0)) PAGE_SR_DELAY_MSEL
FROM
PS.SDR_WEB_BSCRNC_1DAY SDR
INNER JOIN (SELECT
BSCRNC_ID,
BSCRNC_NAME,
ACCESS_TYPE,
ACCESS_TYPE_ID
FROM
nethouse.DIM_LOC_BSCRNC
GROUP BY
BSCRNC_ID,
BSCRNC_NAME,
ACCESS_TYPE,
ACCESS_TYPE_ID) DIM
ON SDR.BSCRNC_ID = DIM.BSCRNC_ID
AND DIM.ACCESS_TYPE_ID IN (0,1,2)
INNER JOIN nethouse.DIM_RAT_MAPPING RAT
ON (RAT.RAT = SDR.RAT)
WHERE
( (STARTTIME >= 1461340800
AND STARTTIME < 1461427200) )
AND RAT.ACCESS_TYPE_ID IN (0,1,2)
and SDR.BSCRNC_ID is not null
GROUP BY
STTIME ) ) A;

执行计划如图2所示。

图2 增加JOIN列非空条件（二）