当我们往表中插入数据时，如果表中有索引，则会给插入操作增加更多的工作量。带来的好处是可以提升查询效率。但是这种优劣该如何权衡，则需要通过数据对比来提供佐证。本文我们将对比没有索引、有一个普通索引、有一个唯一索引的性能差距。

结论

• 在只有一个索引（无论普通索引还是唯一索引）和无索引时性能差距不大。（在千万级数据量时，性能差距不超过一倍）。
• 有无索引会随着数据量增加，性能差异也会随之增加。（下面三条线中，有索引的线的斜率要大于无索引的线，所以随着数据量增加，性能差距也会增加）

实验数据

上图中，“无索引”是指导入目标表没有索引；“普通索引”是指导入目标表只有一个普通索引；“唯一索引”是指导入目标表只有一个唯一索引。
可以看到在当前测试场景下，“普通索引”和“唯一索引”的性能接近。
“无索引”和“有索引”都是呈线性变化，即不会因为数量增加，每个方案会变得更加糟糕。（比如指数型变化，那就意味着更加糟糕）
有无索引的性能差异会随着数据量增加而增加，因为两者斜率不同，即喇叭口会越来越大。

测试环境

见《Mysql使用中的性能优化——搭建Mysql的监测服务》

测试方法解读

上图中无索引表结构

DROP TABLE IF EXISTS test_insert_no_index;
CREATE TABLE test_insert_no_index (
    id SERIAL PRIMARY KEY,
    name TEXT
) engine=InnoDB;

有普通索引表结构

CREATE TABLE test_insert_normal_index (
    id SERIAL PRIMARY KEY,
    name TEXT,
    INDEX name_index (name(32))
) engine=InnoDB;

有唯一索引表结构

CREATE TABLE test_insert_unique_index (
    id SERIAL PRIMARY KEY,
    name TEXT,
    UNIQUE INDEX name_index (name(32))
) engine=InnoDB;

然后使用类似下面的指令进行差距插入

INSERT INTO test_insert_normal_index (SELECT * FROM test_insert_src LIMIT 1000000);

完整测试代码

-- 通过从其他表中读取数据源，写入到目标表中，测试索引的比较操作
DROP DATABASE IF EXISTS testdb;
CREATE DATABASE IF NOT EXISTS testdb;
USE testdb;

DROP TABLE IF EXISTS test_insert_src;
CREATE TABLE test_insert_src (
    id SERIAL PRIMARY KEY,
    name TEXT
) engine=InnoDB;

DROP PROCEDURE IF EXISTS test_insert_proc_batch_bulk;
DELIMITER //
CREATE PROCEDURE test_insert_proc_batch_bulk(IN name TEXT, IN fromNum INT, IN toNum INT)
BEGIN
    DECLARE i INT DEFAULT fromNum;
    DECLARE new_names TEXT DEFAULT '';
    SET @sql = 'INSERT INTO test_insert_src (name) VALUES ';
    WHILE i < toNum DO
        SET new_names = CONCAT(name, i);
        SET i = i + 1;
        SET @sql = CONCAT(@sql, '("', new_names, '"),');
    END WHILE;
    SET @sql = LEFT(@sql, LENGTH(@sql) - 1);
    PREPARE stmt FROM @sql;
    EXECUTE stmt;
    DEALLOCATE PREPARE stmt;
    COMMIT;
END //
DELIMITER ;

DROP PROCEDURE IF EXISTS test_insert_proc_batch;
DELIMITER //
CREATE PROCEDURE test_insert_proc_batch(IN name TEXT, IN count INT, IN step INT)
BEGIN
    DECLARE i INT DEFAULT 0;
    WHILE i < count DO
        CALL test_insert_proc_batch_bulk(name, i, i + step);
        SET i = i + step;
    END WHILE;
    COMMIT;
END //
DELIMITER ;

DROP TABLE IF EXISTS test_insert_no_index;
CREATE TABLE test_insert_no_index (
    id SERIAL PRIMARY KEY,
    name TEXT
) engine=InnoDB;

DROP TABLE IF EXISTS test_insert_normal_index;
CREATE TABLE test_insert_normal_index (
    id SERIAL PRIMARY KEY,
    name TEXT,
    INDEX name_index (name(32))
) engine=InnoDB;

DROP TABLE IF EXISTS test_insert_unique_index;
CREATE TABLE test_insert_unique_index (
    id SERIAL PRIMARY KEY,
    name TEXT,
    UNIQUE INDEX name_index (name(32))
) engine=InnoDB;


TRUNCATE TABLE test_insert_src;
CALL test_insert_proc_batch('test', 10000000, 5000);

TRUNCATE TABLE test_insert_no_index;
INSERT INTO test_insert_no_index (SELECT * FROM test_insert_src LIMIT 1000000);
TRUNCATE TABLE test_insert_no_index;
INSERT INTO test_insert_no_index (SELECT * FROM test_insert_src LIMIT 2000000);
TRUNCATE TABLE test_insert_no_index;
INSERT INTO test_insert_no_index (SELECT * FROM test_insert_src LIMIT 3000000);
TRUNCATE TABLE test_insert_no_index;
INSERT INTO test_insert_no_index (SELECT * FROM test_insert_src LIMIT 4000000);
TRUNCATE TABLE test_insert_no_index;
INSERT INTO test_insert_no_index (SELECT * FROM test_insert_src LIMIT 5000000);
TRUNCATE TABLE test_insert_no_index;
INSERT INTO test_insert_no_index (SELECT * FROM test_insert_src LIMIT 6000000);
TRUNCATE TABLE test_insert_no_index;
INSERT INTO test_insert_no_index (SELECT * FROM test_insert_src LIMIT 7000000);
TRUNCATE TABLE test_insert_no_index;
INSERT INTO test_insert_no_index (SELECT * FROM test_insert_src LIMIT 8000000);
TRUNCATE TABLE test_insert_no_index;
INSERT INTO test_insert_no_index (SELECT * FROM test_insert_src LIMIT 9000000);
TRUNCATE TABLE test_insert_no_index;
INSERT INTO test_insert_no_index (SELECT * FROM test_insert_src);

TRUNCATE TABLE test_insert_normal_index;
INSERT INTO test_insert_normal_index (SELECT * FROM test_insert_src LIMIT 1000000);
TRUNCATE TABLE test_insert_normal_index;
INSERT INTO test_insert_normal_index (SELECT * FROM test_insert_src LIMIT 2000000);
TRUNCATE TABLE test_insert_normal_index;
INSERT INTO test_insert_normal_index (SELECT * FROM test_insert_src LIMIT 3000000);
TRUNCATE TABLE test_insert_normal_index;
INSERT INTO test_insert_normal_index (SELECT * FROM test_insert_src LIMIT 4000000);
TRUNCATE TABLE test_insert_normal_index;
INSERT INTO test_insert_normal_index (SELECT * FROM test_insert_src LIMIT 5000000);
TRUNCATE TABLE test_insert_normal_index;
INSERT INTO test_insert_normal_index (SELECT * FROM test_insert_src LIMIT 6000000);
TRUNCATE TABLE test_insert_normal_index;
INSERT INTO test_insert_normal_index (SELECT * FROM test_insert_src LIMIT 7000000);
TRUNCATE TABLE test_insert_normal_index;
INSERT INTO test_insert_normal_index (SELECT * FROM test_insert_src LIMIT 8000000);
TRUNCATE TABLE test_insert_normal_index;
INSERT INTO test_insert_normal_index (SELECT * FROM test_insert_src LIMIT 9000000);
TRUNCATE TABLE test_insert_normal_index;
INSERT INTO test_insert_normal_index (SELECT * FROM test_insert_src);

TRUNCATE TABLE test_insert_unique_index;
INSERT INTO test_insert_unique_index (SELECT * FROM test_insert_src LIMIT 1000000);
TRUNCATE TABLE test_insert_unique_index;
INSERT INTO test_insert_unique_index (SELECT * FROM test_insert_src LIMIT 2000000);
TRUNCATE TABLE test_insert_unique_index;
INSERT INTO test_insert_unique_index (SELECT * FROM test_insert_src LIMIT 3000000);
TRUNCATE TABLE test_insert_unique_index;
INSERT INTO test_insert_unique_index (SELECT * FROM test_insert_src LIMIT 4000000);
TRUNCATE TABLE test_insert_unique_index;
INSERT INTO test_insert_unique_index (SELECT * FROM test_insert_src LIMIT 5000000);
TRUNCATE TABLE test_insert_unique_index;
INSERT INTO test_insert_unique_index (SELECT * FROM test_insert_src LIMIT 6000000);
TRUNCATE TABLE test_insert_unique_index;
INSERT INTO test_insert_unique_index (SELECT * FROM test_insert_src LIMIT 7000000);
TRUNCATE TABLE test_insert_unique_index;
INSERT INTO test_insert_unique_index (SELECT * FROM test_insert_src LIMIT 8000000);
TRUNCATE TABLE test_insert_unique_index;
INSERT INTO test_insert_unique_index (SELECT * FROM test_insert_src LIMIT 9000000);
TRUNCATE TABLE test_insert_unique_index;
INSERT INTO test_insert_unique_index (SELECT * FROM test_insert_src);