mysql 间隙锁

mysql 版本 5.7.2

隔离级别 rr

mysql 间隙锁 ！不是锁定行，也不是锁定某个列，是锁定对应的索引。测试表 tx_test ，age 字段加了索引了。

-- Table structure for tx_test

DROP TABLE IF EXISTS `tx_test`;
CREATE TABLE `tx_test` (
  `id` int(11) NOT NULL,
  `name` varchar(255) COLLATE utf8mb4_bin DEFAULT NULL,
  `age` int(10) unsigned DEFAULT NULL,
  PRIMARY KEY (`id`),
  KEY `age` (`age`),
  KEY `name` (`name`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_bin;

-- Records of tx_test

BEGIN;
INSERT INTO `tx_test` (`id`, `name`, `age`) VALUES (1, '123', 3);
INSERT INTO `tx_test` (`id`, `name`, `age`) VALUES (2, '44', 4);
INSERT INTO `tx_test` (`id`, `name`, `age`) VALUES (3, '55', 5);
INSERT INTO `tx_test` (`id`, `name`, `age`) VALUES (4, '41', 50);
COMMIT;

#session1

begin;

SELECT * from tx_test;

update tx_test set name='aaaaa' where age >1 and age <20;

SELECT * from tx_test;

COMMIT;

#session2

begin;

SELECT * from tx_test;

INSERT INTO tx_test (id, name, age) VALUES (88, '41', 77);

SELECT * from tx_test;

COMMIT;

为什么 session2 的 INSERT INTO tx_test (id, name, age) VALUES (88, '41', 77); 会阻塞呢 。session1 的查询不是应该 锁定了 -无穷到 50 吗