下面分析下索引和锁的关系。
1)delete from msg where id=2;
由于id是主键,因此直接锁住整行记录即可。
图5
2)delete from msg where token=’ cvs’;
由于token是二级索引,因此首先锁住二级索引(两行),接着会锁住相应主键所对应的记录;
图6
3)delete from msg where message=订单号是多少’;
message没有索引,所以走的是全表扫描过滤。这时表上的各个记录都将添加上X锁。
图7
强烈推荐阅读:https://yq.aliyun.com/articles/5533
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