后臺查詢語句SELECTo.orders_id,s.orders_status_name,ot.text,af.affiliate_idFROMordersoLEFTJOINorders_totalotON(o.orders_id=ot.orders_id)LEFTJOINaffilia

后臺查詢語句SELECT o.orders_id, s.orders_status_name, ot.text ,af.affiliate_id

FROM orders o

LEFT JOIN orders_total ot ON (o.orders_id = ot.orders_id)

LEFT JOIN affiliate_sales AS afs ON afs.affiliate_orders_id = o.orders_id

LEFT JOIN affiliate_affiliate AS af ON af.affiliate_id = afs.affiliate_id

LEFT JOIN orders_status s ON o.orders_status = s.orders_status_id

WHERE

s.language_id = '1'

AND (ot.class = 'ot_total' OR ot.orders_total_id IS NULL)

ORDER BY o.orders_id DESC LIMIT 0, 20

有客戶反應某后臺查詢非常慢,通過程序找到對應的sql，如上！

explain發現+----+-------------+-------+--------+----------------------------+----------------------------+---------+-----------------------------+-------+----------------------------------------------+

| id | select_type | table | type | possible_keys

| key

| key_len | ref

| rows | Extra

|

+----+-------------+-------+--------+----------------------------+----------------------------+---------+-----------------------------+-------+----------------------------------------------+

| 1 | SIMPLE

| s

| ALL | PRIMARY

| NULL

| NULL | NULL

| 21 | Using where; Using temporary; Using filesort |

| 1 | SIMPLE

| o

| ref | orders_status

| orders_status

| 4

| banggood.s.orders_status_id | 31747 |

|

| 1 | SIMPLE

| ot | ref | idx_orders_total_orders_id | idx_orders_total_orders_id | 4

| banggood.o.orders_id

| 19 | Using where

|

| 1 | SIMPLE

| afs | ref | PRIMARY

| PRIMARY

| 4

| banggood.o.orders_id

| 11 | Using index

|

| 1 | SIMPLE

| af | eq_ref | PRIMARY

| PRIMARY

| 4

| banggood.afs.affiliate_id |

1 | Using index

|

+----+-------------+-------+--------+----------------------------+----------------------------+---------+-----------------------------+-------+----------------------------------------------+

s表被作為驅動表，s表為全表掃描,o表使用了status類型的可選擇性非常低的字段作為索引。

初步一看就知道索引使用不恰當！

我們可以看到這條語句where條件中，沒有什么合適的可驅動條件；但是，在order by中，發現order by o.orders_id(orders_id為orders表的主鍵)。我們就可以利用這個特性！

強制使用orders表的orders_id索引進行驅動！

更改如下：EXPLAIN SELECT o.orders_id, s.orders_status_name, ot.text ,af.affiliate_id

FROM orders o FORCE INDEX(PRIMARY)

LEFT JOIN orders_total ot ON (o.orders_id = ot.orders_id)

LEFT JOIN affiliate_sales AS afs ON afs.affiliate_orders_id = o.orders_id

LEFT JOIN affiliate_affiliate AS af ON af.affiliate_id = afs.affiliate_id

LEFT JOIN orders_status s ON o.orders_status = s.orders_status_id

WHERE

s.language_id = '1'

AND (ot.class = 'ot_total' OR ot.orders_total_id IS NULL)

ORDER BY o.orders_id DESC LIMIT 0, 20;

+----+-------------+-------+--------+----------------------------+----------------------------+---------+--------------------------------+------+-------------+

| id | select_type | table | type | possible_keys

| key

| key_len | ref

| rows | Extra

|

+----+-------------+-------+--------+----------------------------+----------------------------+---------+--------------------------------+------+-------------+

| 1 | SIMPLE

| o

| index | NULL

| PRIMARY

| 4

| NULL

| 1 |

|

| 1 | SIMPLE

| s

| eq_ref | PRIMARY

| PRIMARY

| 8

| banggood.o.orders_status,const | 1 | Using where |

| 1 | SIMPLE

| ot | ref | idx_orders_total_orders_id | idx_orders_total_orders_id | 4

| banggood.o.orders_id

| 19 | Using where |

| 1 | SIMPLE

| afs | ref | PRIMARY

| PRIMARY

| 4

| banggood.o.orders_id

| 11 | Using index |

| 1 | SIMPLE

| af | eq_ref | PRIMARY

| PRIMARY

| 4

| banggood.afs.affiliate_id

| 1 | Using index |

+----+-------------+-------+--------+----------------------------+----------------------------+---------+--------------------------------+------+-------------+

對比兩次profiling；

前者：+--------------------------------+------------+-----------+------------+--------------+---------------+

| Status

| Duration | CPU_user | CPU_system | Block_ops_in | Block_ops_out |

+--------------------------------+------------+-----------+------------+--------------+---------------+

| starting

| 0.000027 | 0.000000 | 0.000000 |

0 |

0 |

| Waiting for query cache lock | 0.000006 | 0.000000 | 0.000000 |

0 |

0 |

| checking query cache for query | 0.000130 | 0.000000 | 0.000000 |

0 |

0 |

| checking permissions

| 0.000007 | 0.000000 | 0.000000 |

0 |

0 |

| checking permissions

| 0.000003 | 0.000000 | 0.000000 |

0 |

0 |

| checking permissions

| 0.000003 | 0.000000 | 0.000000 |

0 |

0 |

| checking permissions

| 0.000003 | 0.000000 | 0.000000 |

0 |

0 |

| checking permissions

| 0.000007 | 0.000000 | 0.000000 |

0 |

0 |

| Opening tables

| 0.000130 | 0.000000 | 0.000000 |

0 |

8 |

| System lock

| 0.000017 | 0.000000 | 0.000000 |

0 |

0 |

| Waiting for query cache lock | 0.000033 | 0.000000 | 0.000000 |

0 |

0 |

| init

| 0.000057 | 0.000000 | 0.000000 |

0 |

0 |

| optimizing

| 0.000026 | 0.000000 | 0.000000 |

0 |

0 |

| statistics

| 0.000041 | 0.000000 | 0.000000 |

0 |

0 |

| preparing

| 0.000031 | 0.000000 | 0.000000 |

0 |

0 |

| Creating tmp table

| 0.000111 | 0.001000 | 0.000000 |

0 |

0 |

| executing

| 0.000007 | 0.000000 | 0.000000 |

0 |

0 |

| Copying to tmp table

| 3.541123 | 0.968852 | 2.357642 |

75800 |

0 |

| converting HEAP to MyISAM

| 0.239566 | 0.038994 | 0.198969 |

0 |

262152 |

| Copying to tmp table on disk | 174.185144 | 13.864893 | 35.361625 |

2135152 |

2500280 |

| Sorting result

| 20.923419 | 0.127980 | 3.017541 |

2770408 |

27536 |

| Sending data

| 0.045078 | 0.000000 | 0.002999 |

1208 |

0 |

| end

| 0.000018 | 0.000000 | 0.000000 |

0 |

0 |

| removing tmp table

| 0.881884 | 0.018997 | 0.160976 |

760 |

8 |

| end

| 0.003960 | 0.000000 | 0.002000 |

448 |

0 |

| query end

| 0.000012 | 0.000000 | 0.000000 |

0 |

0 |

| closing tables

| 0.031745 | 0.000000 | 0.000999 |

936 |

0 |

| freeing items

| 0.015499 | 0.000000 | 0.003000 |

808 |

0 |

| Waiting for query cache lock | 0.000017 | 0.000000 | 0.000000 |

0 |

0 |

| freeing items

| 0.000791 | 0.000000 | 0.000000 |

0 |

0 |

| Waiting for query cache lock | 0.000009 | 0.000000 | 0.000000 |

0 |

0 |

| freeing items

| 0.000003 | 0.000000 | 0.000000 |

0 |

0 |

| storing result in query cache | 0.000009 | 0.000000 | 0.000000 |

0 |

0 |

| logging slow query

| 0.000003 | 0.000000 | 0.000000 |

0 |

0 |

| logging slow query

| 0.000010 | 0.000000 | 0.000000 |

0 |

0 |

| cleaning up

| 0.000007 | 0.000000 | 0.000000 |

0 |

0 |

+--------------------------------+------------+-----------+------------+--------------+---------------+

各種cpu，io損耗，慘不忍睹！其中最大的消耗是Copying to tmp table on disk。

本文原創發布php中文網，轉載請注明出處，感謝您的尊重！

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