数据库并发事务问题图解 Dirty read Lost to modify Unrepeatableread Phantom read 不可重复读和幻读区别 Dirty read 当一个事务A正在访问数据并且对数据进行了修改,但是这次修改还没有提交到数据库中,此时另外一个事务B也访问了这个数据,然后使用了这个数据。因为这个数据还是提交前的数据,此时另一个事务B读到的数...
3,P2(Fuzzy or Non-Repeatable Read) 最小化为 G2-item(Item Anti-dependency Cycles) :DSG中包含环,且其中至少有一条关于某个object的rw冲突 4,P3(Phantom) 最小化为 G2(Anti-dependency Cycles): DSG中包含环,并且其中至少有一条是rw冲突,仍然以上面的H3为例: H3:r1[P] w2[insert y to P] r2[z...
Non-repeatable reads Phantom reads What is Dirty Read? The simplest explanation of the dirty read is the state of reading uncommitted data. In this circumstance, we are not sure about the consistency of the data that is read because we don’t know the result of the open transaction(s)...
脏读(dirty reads)一个事务读取了另一个未提交的并行事务写的数据。 不可重复读(non-repeatable reads) 一个事务重新读 … blog.163.com|基于302个网页 2. 脏读取 ●脏读取(Dirty Reads):一个事务开始读取了某行数据,但是另外一个事务已经更新了此数据但没有能够及时提交。这是相 … ...
Common concurrency issues often fall into one of four categories: unclean reads, lost reads, non-repeatable reads, and phantom reads. A dirty read occurs when a transaction is permitted to read a row that has been updated by another transaction but has not yet been committed. Several uncommitte...
Unlike (7) michael vessey (5/23/2012) this is something that itzik ben-gan demos at some of conferences he talks at he's doesn't say don't use read uncommitted, just know when and where to use it and be aware of the risk (albeit a risk that is very rarely actually hits anyone)...
2) When the transaction isolation level is Repeatable-Read or Serializable, and the connections are pooled. As long as no update is made on the specific thread, the transaction isn't closed; so new HTTP requests handled by the same thread would re-use the connection and therefore, the ...