提交读，未提交读，可重复读，可串行读。
Read committed, Read uncommitted, Repeatable Read, Serializable.
比如，读取只读的查找表不需要可重复读级别，未提交读级别就足够了。
For example, reading from a read - only look up table doesn t require repeatable read, and uncommitted read is sufficient.
支持表级和行级锁以及4个隔离级别：RR(可重复读)、RS(读可靠)、CS(默认——游标可靠)和UR(未提交读)。
Supports table and row level locking and 4 isolation levels, RR (repeatable read), rs (read stability), CS (default - cursor stability) and ur (uncommitted read).
例如，如果一个成员正在更新一行数据，那么另一个成员就不能以未提交读(uncommitted read)以外的任何隔离级别读取这一行。
For example, if one member is updating a row, it would not be proper for another member to read the row with any other isolation level than uncommitted read.
释放行锁，以便其他应用程序可以对表执行SELECT、INSERT、UPDATE和DELETE(例如，使用游标稳定性(curs or stability)隔离级别或未提交读(uncommitted read)隔离级别)。
Release the row locks so that other applications can SELECT, INSERT, UPDATE, and DELETE from the table (for example, use isolation level cursor stability or uncommitted read).
将分割镜像初始化为快照时，将执行崩溃恢复，回滚所有未提交的事务，并使数据库可以被所有读或写操作访问。
The initialization of the split mirror as snapshot performs a crash recovery, rolls back all uncommitted transactions, and makes the database available for any read or write operation.
会发生不可重读、幻像读和读未提交数据。
An unrepeatable read, phantom read, and reads of uncommitted data can occur.
脏读：A 1检索a 2未提交的数据。
脏读：A 1检索a 2未提交的数据。
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