MySQL table - performance, count of indexes - mysql

Question

I have table with this structure:
CREATE TABLE `supplies` (
`cycle_id` int(11) NOT NULL,
`subject_id` varchar(45) COLLATE utf8_unicode_ci NOT NULL,
`market_id` int(11) NOT NULL,
`price` int(11) NOT NULL,
`currency_id` varchar(45) COLLATE utf8_unicode_ci DEFAULT NULL,
`offered_order` bigint(20) DEFAULT NULL,
PRIMARY KEY (`subject_id`,`market_id`,`cycle_id`,`price`),
KEY `fk_supplies_subjects` (`subject_id`),
KEY `fk_supplies_markets` (`market_id`),
KEY `fk_supplies_currencies` (`currency_id`),
CONSTRAINT `fk_supplies_currencies` FOREIGN KEY (`currency_id`) REFERENCES `currencies` (`currency_id`) ON DELETE CASCADE ON UPDATE CASCADE,
CONSTRAINT `fk_supplies_subjects` FOREIGN KEY (`subject_id`) REFERENCES `subjects` (`subject_id`) ON DELETE CASCADE ON UPDATE CASCADE,
CONSTRAINT `fk_supplies_markets` FOREIGN KEY (`market_id`) REFERENCES `markets` (`market_id`) ON DELETE CASCADE ON UPDATE CASCADE
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci
Table has about 20,000 rows. I have problems with performance. I am logging SQL queries that are taking long time and from the log I can see:
Slow INSERTs into table.
INSERT INTO supplies VALUES (11, 'userName', 18, 30, 'pound', 20) ;
Slow DELETEs from table
DELETE FROM supplies WHERE cycle_id = 6 AND market_id = 18 AND subject_id = 'userName' ;
What could I improve?
I guess, changing the indexes would help, because the PRIMARY key is formed from 4 columns (and some are even varchars). But how should I change the indexes?
Thanks everyone.

Answer 1

You should create a primary key with only one field. This is a basic performance optimization
CREATE TABLE `supplies` (
`supplies_id` int(11) NOT NULL AUTO_INCREMENT,
`cycle_id` int(11) NOT NULL,
`subject_id` varchar(45) COLLATE utf8_unicode_ci NOT NULL,
`market_id` int(11) NOT NULL,
`price` int(11) NOT NULL,
`currency_id` varchar(45) COLLATE utf8_unicode_ci DEFAULT NULL,
`offered_order` bigint(20) DEFAULT NULL,
PRIMARY KEY (`supplies_id`),
INDEX `index` (`subject_id` ASC,`market_id` ASC,`cycle_id` ASC,`price` ASC))
KEY `fk_supplies_subjects` (`subject_id`),
KEY `fk_supplies_markets` (`market_id`),
KEY `fk_supplies_currencies` (`currency_id`),
CONSTRAINT `fk_supplies_currencies` FOREIGN KEY (`currency_id`) REFERENCES `currencies` (`currency_id`) ON DELETE CASCADE ON UPDATE CASCADE,
CONSTRAINT `fk_supplies_subjects` FOREIGN KEY (`subject_id`) REFERENCES `subjects` (`subject_id`) ON DELETE CASCADE ON UPDATE CASCADE,
CONSTRAINT `fk_supplies_markets` FOREIGN KEY (`market_id`) REFERENCES `markets` (`market_id`) ON DELETE CASCADE ON UPDATE CASCADE
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci
Another possible improvement can be removing cascade constraints. Check if they are really necessary.