数据库事务转载基础二：oracle事务隔离级别

Oracle 支持的 2 种事务隔离级别 Read committed ， Serializable

 

来自 oracle 官方网站的 Read committed ， Serializable 的解释

 

Isolation Level	Description
Read committed	This is the default transaction isolation level. Each query executed by a transaction sees only data that was committed before the query (not the transaction) began. An Oracle query never reads dirty (uncommitted) data. Because Oracle does not prevent other transactions from modifying the data read by a query, that data can be changed by other transactions between two executions of the query. Thus, a transaction that runs a given query twice can experience both nonrepeatable read and phantoms.
Serializable	Serializable transactions see only those changes that were committed at the time the transaction began, plus those changes made by the transaction itself through INSERT , UPDATE , and DELETE statements. Serializable transactions do not experience nonrepeatable reads or phantoms.

 

 

 

2 者的区别也是来自官方网站

summarizes key differences between read committed and serializable transactions in Oracle.

Table 13-2 Read Committed and Serializable Transactions

	Read Committed	Serializable
Dirty write	Not possible	Not possible
Dirty read	Not possible	Not possible
Nonrepeatable read	Possible	Not possible
Phantoms	Possible	Not possible

 

 

上面的 2 个表来自 http://download-west.oracle.com/docs/cd/B19306_01/server.102/b14220/consist.htm