dirty mature

lock for INSERT, UPDATE, delete is also releasedAlthough deadlock cannot be avoided in this way, the two-segment locking protocol ensures that concurrent scheduling of transactions is serialized (serialization is important, especially when data recovery and backup). Lock mode in a transactionFour isolation levels for transactionsin the database operation, the transaction isolation level is proposed in order to effectively guarantee the correctness of concurrent read data. Our database locks al

share the lock, but not the lock), before the write operation to request and obtain an X lock (exclusive lock, other transactions can no longer acquire any locks). The lock does not succeed, the transaction goes into a wait state until locking succeeds to continue execution. Unlocking phase: When a transaction releases a block, the transaction enters the unlock phase, and the lock operation is no longer allowed at this stage. While this approach does not prevent deadlocks, the two-phas

write lock mutex, this can effectively avoid phantom reading, non-repeatable read, dirty reading problems, but will greatly reduce the concurrency of the database. Therefore, the most important difference between non-repeatable reading and phantom reading is how to solve their problems by locking mechanism. As mentioned above, the use of pessimistic locking mechanism to deal with these two problems, but MySQL, ORACLE, PostgreSQL and other

Phantom read, can not be avoided by row lock. Need to serializable isolation level, read lock, write with write lock, read lock and write lock mutex, this can effectively avoid phantom reading, non-repeatable read, dirty reading problems, but will greatly reduce the concurrency of the database. Therefore, the most important difference between non-repeatable reading and phantom reading is how to solve their problems by locking mechanism. As mentioned

serializable isolation level, read lock, write with write lock, read lock and write lock mutex, this can effectively avoid phantom reading, non-repeatable read, dirty reading problems, but will greatly reduce the concurrency of the database.Therefore, the most important difference between non-repeatable reading and phantom reading is how to solve their problems by locking mechanism.As mentioned above, the use of pessimistic locking mechanism to deal

write lock mutex, this can effectively avoid phantom reading, non-repeatable read, dirty reading problems, but will greatly reduce the concurrency of the database. Therefore, the most important difference between non-repeatable reading and phantom reading is how to solve their problems by locking mechanism. As mentioned above, the use of pessimistic locking mechanism to deal with these two problems, but MySQL, ORACLE, PostgreSQL and other

Original link http://www.cnblogs.com/chenpingzhao/p/5107480.htmlFirst, IntroductionConsider this scenario : If the redo log can grow infinitely and the buffer pool is large enough, it is not necessary to flush the new version of the pages in the buffer pool back to disk. Because when a outage occurs, it is entirely possible to redo the log to recover the data from the entire database system to the time of the outage.However, this requires two prerequisites: 1, the buffer pool can cache all the d

, dirty reading problems, but will greatly reduce the concurrency of the database.Therefore, the most important difference between non-repeatable reading and phantom reading is how to solve their problems by locking mechanism.As mentioned above, the use of pessimistic locking mechanism to deal with these two problems, but MySQL, ORACLE, PostgreSQL and other mature databases, for performance reasons, are usi

MySQL Tutorial: About the checkpoint Mechanism I. Introduction Think about this scenario: If the redo log can be infinitely increased and the buffer pool is large enough, you do not need to refresh the new version of the page in the buffer pool to the disk. When a crash occurs, you can use the redo log to restore the data in the entire database system to the time when the crash occurs. However, this requires two prerequisites: 1. The buffer pool can cache all the data in the database; 2. Redo lo

. If there is no idle page in the buffer pool, you need to put a page into the buffer pool. If it is a dirty page, you need to flush to the disk. Here, another LRU algorithm is required. A page contains multiple records. The page format must be designed to support variable-length fields. If this happens, the data in the buffer pool will be lost. This requires the REDO log to write the changes to the data to the redo log first, then write the buffer po

people inside and outside Chongyang, and there is always a feeling that the joint venture vehicle technology is mature and indeed mature. The technology that lags behind the foreign countries for 30 years is also very popular. Foreign brands are mainly used to buy brands and sell well-known brands. Chinese people have a good face and feel that it is easy to drive a taxi. If you are an IT company, you will

problematic processes. (Of course, the above-mentioned flashback occurs frequently in the conventional process, so it is directly uninstalled. Therefore, the bottom-layer objc users should use the server to protect the client experience carefully) Null Pointer:When Java first came out, the biggest selling point was: no pointer complexity. Indeed, GC is a great progress of the language, looking at today's Java virtual machine that has exceeded the Java language itself, we can see its value. objc

Comparison between AngularJS, Backbone. js, and Ember. js, angularjsbackbone1 Introduction In this article, we are going to compare three popular Web "Model-View-*" frameworks: AngularJS, Backbone, and Ember. Choosing the right framework for your project will have a huge impact on your ability to deliver your project in a timely manner and your ability to maintain your own code in the future. You may want to build a project based on a reliable, stable, and m