Read committed, Read uncommitted, Repeatable Read, Serializable.
提交读，未提交读，可重复读，可串行读。
Repeatable read — the transaction always reads the same data during the transaction.
Repeatable read(可重读)——在事务过程中，事务始终读取相同的数据。
For example, reading from a read - only look up table doesn t require repeatable read, and uncommitted read is sufficient.
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。
Supports table and row level locking and 4 isolation levels, RR (repeatable read), rs (read stability), CS (default - cursor stability) and ur (uncommitted read).
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)。
However, for entity beans this rule has to be relaxed; due to the nature of the model, most pessimistic locking access intents require at least Repeatable Read.
但是，对于实体Bean则可不遵循此规则，由于该模型本身的特性，多数悲观锁定访问都需要至少Repeatable Read。
In fact, the only row-level locking that remains during INSERT is the next-key locks that are required to protect an INSERT from adding keys to repeatable read scanners.
实际上，在INSERT期间惟一保持的行级锁是next - key锁，这个锁用于使INSERT不会添加键到可重复的读扫描器。
With the "Repeatable Read" data region fetch requests issued multiple times within the same transaction will always produce the same result yielding better application throughput.
在相同事务下对“可重复读取”区域内数据的多次请求的结果是相同的，但能够带来更好的应用吞吐量。
These next key locks are only obtained when the key INSERT finds that a scanner with a Repeatable Read (RR) isolation level has a row lock on the next-higher key in the index.
这些nextkey锁只有在keyINSERT发现带有Repeatable Read (RR)隔离级别的扫描器在索引中的next -higher键上有一个行锁时才能获得。
These next key locks are only obtained when the key INSERT finds that a scanner with a Repeatable Read (RR) isolation level has a row lock on the next-higher key in the index.
这些nextkey锁只有在keyINSERT发现带有Repeatable Read (RR)隔离级别的扫描器在索引中的next -higher键上有一个行锁时才能获得。
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