[英]Why does MySQL not use optimal indexes
我正在嘗試優化查詢,但是,MySQL似乎在查詢上使用了非最佳索引,而且我似乎無法弄清楚出了什么問題。 我的查詢如下:
SELECT SQL_CALC_FOUND_ROWS deal_ID AS ID,dealTitle AS dealSaving,
storeName AS title,deal_URL AS dealURL,dealDisclaimer,
dealType, providerName,providerLogo AS providerIMG,createDate,
latitude AS lat,longitude AS lng,'local' AS type,businessType,
address1,city,dealOriginalPrice,NULL AS dealDiscountPercent,
dealPrice,scoringBase, smallImage AS smallimage,largeImage AS image,
storeURL AS storeAlias,
exp(-power(greatest(0,
abs(69.0*DEGREES(ACOS(0.82835377099147 *
COS(RADIANS(latitude)) * COS(RADIANS(-118.4-longitude)) +
0.56020534635454*SIN(RADIANS(latitude)))))-2),
2)/(5.7707801635559)) *
scoringBase * IF(submit_ID IN (18381),
IF(businessType = 1,1.3,1.2),IF(submit_ID IN (54727),1.19, 1)
) AS distance
FROM local_deals
WHERE latitude BETWEEN 33.345362318841 AND 34.794637681159
AND longitude BETWEEN -119.61862872928 AND -117.18137127072
AND state = 'CA'
AND country = 'US'
ORDER BY distance DESC
LIMIT 48 OFFSET 0;
列出表上的索引將顯示:
+-------------+------------+-----------------+--------------+-----------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
+-------------+------------+-----------------+--------------+-----------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| local_deals | 0 | PRIMARY | 1 | id | A | 193893 | NULL | NULL | | BTREE | | |
| local_deals | 0 | unique_deal_ID | 1 | deal_ID | A | 193893 | NULL | NULL | | BTREE | | |
| local_deals | 1 | deal_ID | 1 | deal_ID | A | 193893 | NULL | NULL | | BTREE | | |
| local_deals | 1 | store_ID | 1 | store_ID | A | 193893 | NULL | NULL | YES | BTREE | | |
| local_deals | 1 | storeOnline_ID | 1 | storeOnline_ID | A | 3 | NULL | NULL | YES | BTREE | | |
| local_deals | 1 | storeChain_ID | 1 | storeChain_ID | A | 117 | NULL | NULL | YES | BTREE | | |
| local_deals | 1 | userProvider_ID | 1 | userProvider_ID | A | 5 | NULL | NULL | YES | BTREE | | |
| local_deals | 1 | expirationDate | 1 | expirationDate | A | 3127 | NULL | NULL | YES | BTREE | | |
| local_deals | 1 | createDate | 1 | createDate | A | 96946 | NULL | NULL | YES | BTREE | | |
| local_deals | 1 | city | 1 | city | A | 17626 | NULL | NULL | YES | BTREE | | |
| local_deals | 1 | state | 1 | state | A | 138 | NULL | NULL | YES | BTREE | | |
| local_deals | 1 | zip | 1 | zip | A | 38778 | NULL | NULL | YES | BTREE | | |
| local_deals | 1 | country | 1 | country | A | 39 | NULL | NULL | YES | BTREE | | |
| local_deals | 1 | latitude | 1 | latitude | A | 193893 | NULL | NULL | YES | BTREE | | |
| local_deals | 1 | longitude | 1 | longitude | A | 193893 | NULL | NULL | YES | BTREE | | |
| local_deals | 1 | eventDate | 1 | eventDate | A | 4215 | NULL | NULL | YES | BTREE | | |
| local_deals | 1 | isNowDeal | 1 | isNowDeal | A | 3 | NULL | NULL | YES | BTREE | | |
| local_deals | 1 | businessType | 1 | businessType | A | 5 | NULL | NULL | YES | BTREE | | |
| local_deals | 1 | dealType | 1 | dealType | A | 5 | NULL | NULL | YES | BTREE | | |
| local_deals | 1 | submit_ID | 1 | submit_ID | A | 5 | NULL | NULL | YES | BTREE | | |
+-------------+------------+-----------------+--------------+-----------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
運行說明擴展顯示:
+------+-------------+-------------+------+----------------------------------+-------+---------+-------+-------+----------+----------------------------------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | filtered | Extra |
+------+-------------+-------------+------+----------------------------------+-------+---------+-------+-------+----------+----------------------------------------------------+
| 1 | SIMPLE | local_deals | ref | state,country,latitude,longitude | state | 35 | const | 52472 | 100.00 | Using index condition; Using where; Using filesort |
+------+-------------+-------------+------+----------------------------------+-------+---------+-------+-------+----------+----------------------------------------------------+
表格中大約有20萬行。 奇怪的是它忽略了緯度和經度索引,因為它們應該更多地過濾表。 在刪除命令的“州”和“國家”的地方運行查詢,可以得到以下解釋:
+------+-------------+-------------+-------+--------------------+-----------+---------+------+-------+----------+----------------------------------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | filtered | Extra |
+------+-------------+-------------+-------+--------------------+-----------+---------+------+-------+----------+----------------------------------------------------+
| 1 | SIMPLE | local_deals | range | latitude,longitude | longitude | 5 | NULL | 30662 | 100.00 | Using index condition; Using where; Using filesort |
+------+-------------+-------------+-------+--------------------+-----------+---------+------+-------+----------+----------------------------------------------------+
這表明經度索引可以更好地將表篩選為30,662行。 我在這里想念什么嗎? 如何獲得MySQL以使用所有查詢。 請注意,該表是InnoDB,並且我正在使用MySQL 5.5。
您查詢的最佳索引是(country, state, latitude, longitude)
的綜合索引(country, state, latitude, longitude)
可以交換country
state
)。 MySQL在這里提供了有關多列索引的良好文檔。
基本上, latitude
和longitude
並不是單獨選擇的。 不幸的是,標准B樹索引僅支持一個不等式,而您的查詢有兩個。
實際上,如果要進行GIS處理,則應使用MySQL的空間擴展。
根據表的大小,Gordon建議的索引可能“足夠好”。 如果需要更高的性能,則需要使用2D分區技術,其中您可以按latitude
分區,並安排InnoDB PRIMARY KEY
以longitude
開頭。 我的文章中提供了更多詳細信息和示例代碼。
解決此類問題的一種通用技術是使用以下屬性構建子查詢:
LIMIT
個; 這些就是您所需要的。 PRIMARY KEY
”都有一個“覆蓋索引”。 就像是
SELECT b. ..., a.distance
FROM local_deals b
JOIN (
SELECT id,
(...) AS distance,
FROM local_deals
WHERE latitude BETWEEN 33.34536 AND 34.79464
AND longitude BETWEEN -119.61863 AND -117.18137
AND state = 'CA'
AND country = 'US'
ORDER BY distance ASC
LIMIT 48 OFFSET 0
) AS a ON b.id = a.id
ORDER BY a.distance;
INDEX(country, state, latitude, longitude, id) -- `id` is the PK
-- country and state first (because of '='); id last.
為什么這有幫助...
當使用“巨大”表(其中I / O占主導)時,這種技術可以算作:
id
48( LIMIT
)次隨機獲取將獲得48行。 如果沒有子查詢,則需要獲取龐大的行。 並且,根據所使用的索引,最多可以提取30K塊。 那要慢幾個數量級。
同樣,將48行與30K行進行比較以寫入排序表( ORDER BY
)。
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