Help Center/ GaussDB(DWS)/ Performance Tuning/ Optimization Cases/ Case: Adding NOT NULL for JOIN Columns
Updated on 2023-03-30 GMT+08:00
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Case: Adding NOT NULL for JOIN Columns

Symptom

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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 ) ) ;

Figure 1 shows the execution plan.

Figure 1 Adding NOT NULL for JOIN columns (1)

Optimization Analysis

  1. As shown in Figure 1, the sequential scan phase is time consuming.
  2. The JOIN performance is poor because a large number of null values exist in the JOIN column BSCRNC_ID of the PS.SDR_WEB_BSCRNC_1DAY table.

    Therefore, you are advised to manually add NOT NULL for JOIN columns in the statement, as shown below:

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    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;

    The following figure shows the execution plan.

    Figure 2 Adding NOT NULL for JOIN columns (2)
Parent topic: Optimization Cases