I hate the way you talk to me
And the way you cut your hair
I hate the way you drive my car
I hate it when you stare
I hate your big dumb combat boots
And the way you read my mind
I hate you so much, that it makes me sick
And even makes me rhyme
I hate the way you're always right
I hate it when you lie
I hate it when you make me laugh
Even worse when you make me cry
I hate it when you not around
And the fact that you didn't call
But mostly I hate the way I don't hate you
Not even close
Not even a little bit
Not even at all

#mysql# 这是一条定时发送的微博，本人还在睡觉！

》图1,2,3：SQL 标准事务隔离级别（Oracle 默认“读提交”，mysql默认“可重复读”需修改）：
1)读未提交（read uncommitted 一个事务还没提交时，它做的变更就能被别的事务看到）
2)读提交（read committed 一个事务提交之后，它做的变更才会被其他事务看到）
3)可重复读（repeatable read 一个事务执行过程中看到的数据，总是跟这个事务在启动时看到的数据是一致的且对其他事务不可见）
4)串行化（serializable 对于同一行记录，“写”会加“写锁”，“读”会加“读锁”，当出现读写锁冲突的时候，后访问的事务必须等前一个事务执行完成，才能继续执行）

》图4，本期作业：在 information_schema 库的 innodb_trx 这个表中监控长事务（比如：超过 60s 的事务）
select * from information_schema.innodb_trx where TIME_TO_SEC(timediff(now(),trx_started))>60

》图4，上期作业：备份是强需求，至于多少合适，还是得平衡业务需求和存储成本

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