Lost Update | Dirty Read | Unrepeatable Read | Phantom Read

最新推荐文章于 2024-06-28 08:24:41 发布

柏油路留不下脚印

最新推荐文章于 2024-06-28 08:24:41 发布

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分类专栏： database 文章标签： transactions

本文链接：https://blog.youkuaiyun.com/wwq518/article/details/51262207

Lost Update
丢失更新：提交或者回滚一个事务，把其它事务已提交的更新的数据覆盖了。
If the two transactions want to change the same columns, the second transaction will overwrite the first one, therefore losing the first transaction update.
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In this example Bob is not aware that Alice has just changed the quantity from 7 to 6, so her UPDATE is overwritten by Bob’s change.

A lost update is a typical problem in transaction processing in SQL. It happens when two queries access and update the same data from a database. This problem can be understood by the below given diagram. Here, A is processing an order for a client for 150 items. He checks from the ITEMS table that there are 300 available items. So he starts placing the order. After few seconds B gets an order for 200 items. He also checks the items table and finds that there are 300 items available. So he also starts placing an order. Meanwhile,