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[英]Slow query after migrating WHERE EXISTS (SUBQUERY) from MySQL 5.7 to MARIADB 10.6
[英]EXPLAIN Shows “DEPENDENT SUBQUERY” and very slow after migrating from MariaDB to MySQL
我正在使用mysqldump方法使用Mysql 5.7從舊的MariaDB 10.0數據庫遷移到新的Google Cloud Sql。 遷移之后,我得到了有關WHERE EXISTS語句的一些非常慢的查詢。
我試圖在我的舊數據庫和新數據庫上解釋我的查詢,它解釋了不同的結果。 由於它使用轉儲,因此我假設表索引沒有變化。 這是我想運行的查詢
SELECT * FROM detitem
where exists (select 1 from detlayanan
where detitem.iddetlayanan = detlayanan.id
and detlayanan.layanan_idlayanan='LYN15176176101503')
舊數據庫的解釋
+------+-------------+------------+------+------------------------------------+----------------------------+---------+--------------------------------+-------+--------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+------+-------------+------------+------+------------------------------------+----------------------------+---------+--------------------------------+-------+--------------------------+
| 1 | PRIMARY | detlayanan | ref | PRIMARY,fk_detlayanan_layanan1_idx | fk_detlayanan_layanan1_idx | 22 | const | 11030 | Using where; Using index |
| 1 | PRIMARY | detitem | ref | FK_detitem_detlayanan | FK_detitem_detlayanan | 52 | citridia_sinadme.detlayanan.id | 1 | |
+------+-------------+------------+------+------------------------------------+----------------------------+---------+--------------------------------+-------+--------------------------+
和來自新數據庫的解釋
+----+--------------------+------------+------------+--------+------------------------------------+---------+---------+---------------------------------------+---------+----------+-------------+
| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra |
+----+--------------------+------------+------------+--------+------------------------------------+---------+---------+---------------------------------------+---------+----------+-------------+
| 1 | PRIMARY | detitem | NULL | ALL | NULL | NULL | NULL | NULL | 2079094 | 100.00 | Using where |
| 2 | DEPENDENT SUBQUERY | detlayanan | NULL | eq_ref | PRIMARY,fk_detlayanan_layanan1_idx | PRIMARY | 52 | citridia_sinadme.detitem.iddetlayanan | 1 | 5.00 | Using where |
+----+--------------------+------------+------------+--------+------------------------------------+---------+---------+---------------------------------------+---------+----------+-------------+
即使存在索引,新程序也會執行全表掃描。 我在這里想念什么嗎?
這是“ detlayanan”表
CREATE TABLE `detlayanan` (
`transaksi_idtransaksi` varchar(40) NOT NULL,
`layanan_idlayanan` varchar(20) NOT NULL,
`nama_layanan` varchar(255) DEFAULT NULL,
`jumlah_beli` float DEFAULT NULL,
`id` varchar(50) NOT NULL,
`harga` decimal(20,2) DEFAULT '0.00',
`hargatotal` decimal(20,2) DEFAULT '0.00',
`luas_p` double(255,2) DEFAULT '0.00',
`luas_l` double(255,2) DEFAULT '0.00',
`luas_q` double(255,2) DEFAULT '0.00',
`keterangan` varchar(255) DEFAULT '',
`iddeposit` varchar(255) DEFAULT NULL,
`posisi` tinyint(4) DEFAULT '1',
`idworkshop` varchar(60) DEFAULT NULL,
`is_wsot` tinyint(4) DEFAULT '0',
`created_at` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP,
`updated_at` timestamp NOT NULL DEFAULT '0000-00-00 00:00:00' ON UPDATE CURRENT_TIMESTAMP,
`total_bersih` varchar(20) DEFAULT '0',
`total_min_order` decimal(20,2) DEFAULT '0.00',
`kondisi_barang` text,
PRIMARY KEY (`id`),
KEY `fk_detlayanan_layanan1_idx` (`layanan_idlayanan`),
KEY `fk_detlayanan_deposit` (`iddeposit`),
KEY `transaksi_idtransaksi` (`transaksi_idtransaksi`),
CONSTRAINT `detlayanan_ibfk_1` FOREIGN KEY (`transaksi_idtransaksi`) REFERENCES `transaksi` (`idtransaksi`),
CONSTRAINT `fk_detlayanan_layanan1` FOREIGN KEY (`layanan_idlayanan`) REFERENCES `layanan` (`idlayanan`) ON DELETE NO ACTION ON UPDATE NO ACTION
)
這是“細節”表
CREATE TABLE `detitem` (
`item_iditem` varchar(20) NOT NULL,
`layanan_idlayanan` varchar(255) NOT NULL,
`jumlah_item` int(255) DEFAULT NULL,
`transaksi_idtransaksi` varchar(255) NOT NULL,
`id` varchar(50) NOT NULL,
`iddetlayanan` varchar(50) NOT NULL,
`created_at` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP,
`updated_at` timestamp NOT NULL DEFAULT '0000-00-00 00:00:00' ON UPDATE CURRENT_TIMESTAMP,
`hapus` tinyint(4) DEFAULT '0',
PRIMARY KEY (`id`),
KEY `FK_detitem_item` (`item_iditem`),
KEY `FK_detitem_layanan` (`layanan_idlayanan`),
KEY `FK_detitem_transaksi` (`transaksi_idtransaksi`),
KEY `FK_detitem_detlayanan` (`iddetlayanan`),
CONSTRAINT `FK_detitem_detlayanan` FOREIGN KEY (`iddetlayanan`) REFERENCES `detlayanan` (`id`),
CONSTRAINT `FK_detitem_item` FOREIGN KEY (`item_iditem`) REFERENCES `item` (`iditem`),
CONSTRAINT `FK_detitem_layanan` FOREIGN KEY (`layanan_idlayanan`) REFERENCES `layanan` (`idlayanan`),
CONSTRAINT `FK_detitem_transaksi` FOREIGN KEY (`transaksi_idtransaksi`) REFERENCES `transaksi` (`idtransaksi`)
)
我希望解釋的“行數”保持很小,在舊的DB中,即使在另一個表中,“行數”也保持在非常低的水平。 但在新的數據庫中,它最多可以顯示一百萬。
UPDATE
經過一些研究,實際上我必須在where語句中顯式添加一些索引列以伴隨EXISTS語句。 因此查詢將像這樣
SELECT * FROM detitem WHERE
<indexed column> in (<some id's>)
AND EXISTS ( SELECT 1 FROM detlayanan WHERE detitem.iddetlayanan =
detlayanan.id AND detlayanan.layanan_idlayanan = 'LYN15176176101503' )
顯然,MySQL對目標表進行了全面掃描以檢查子查詢值是否存在,當聲明了一些索引列時,sql不需要這樣做。 在MySQL中也發現了這種情況。
一些參考: https : //mariadb.com/kb/en/library/exists-to-in-optimization/
這看起來像MariaDB的Optimizer比MySQL領先一兩個步驟的情況。
看看這是否運作良好:
SELECT i.*
FROM ( SELECT id
FROM detlayanan
WHERE layanan_idlayanan = 'LYN15176176101503'
) AS x
JOIN detitem AS i ON x.id = i.iddetlayanan
我認為它將在兩台服務器上都能很好地工作。
更簡單了:
SELECT i.*
FROM detlayanan AS lay
JOIN detitem AS i ON lay.id = i.iddetlayanan
WHERE lay.layanan_idlayanan = 'LYN15176176101503'
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