transaction and concurrency control

Reading directory (content) 1 Concurrency control theory 1.1 Pessimistic concurrency control 1.2 Optimistic concurrency control 2 Isolation Level 2.1 Isolation Level Description 2.2

Discussion of transaction and concurrency problems in databaseRecently, a colleague wrote a piece of code that was responsible for creating the logic of the order, and the code review found that there might be concurrency problems. Colleagues do not agree that he believes his logic is written in the stored procedure, should be no problem.The logic of the Code is

1. What is a transactionA transaction is a combination of one or more database operation statements with acid,4 characteristics.Atomicity: Either all succeeds or all is undoneIsolation: Transactions are independent from one another and are not interfering with each otherConsistency: The database consistency constraint is not compromised after the database has changed state correctlyPersistence: The commit result of the

MySQL transaction concurrency problem, lock mechanism1. What is a transactionA transaction is a combination of one or more database operation statements with acid,4 characteristics.Atomicity: Either all succeeds or all is undoneIsolation: Transactions are independent from one another and are not interfering with each otherConsistency: The database consistency con

, 2, 1-This time the data is updatedIt can be verified that, under the isolation level of Repeatable-read, a transaction is not aware of data changes outside the transaction, and all the data read is unchanged from the beginning of the transaction, but the operation of the update type is affected by changes in the external data of the

Document directory 2.2.1 concurrency consistency 2.2.2 solutions to concurrency consistency problems 2.2.3 transaction isolation level 2.2 SQL Server 2000 + ADO. Net concurrency control 2.2.1 concurrency consistency Common

1. What is a transactionA transaction is a combination of one or more database operation statements with acid,4 characteristics.Atomicity: Either all succeeds or all is undoneIsolation: Transactions are independent from one another and are not interfering with each otherConsistency: The database consistency constraint is not compromised after the database has changed state correctlyPersistence: The commit result of the

1. What is a transactionA transaction is a combination of one or more database operation statements with acid,4 characteristics.Atomicity: Either all succeeds or all is undoneIsolation: Transactions are independent from one another and are not interfering with each otherConsistency: The database consistency constraint is not compromised after the database has changed state correctlyPersistence: The commit result of the

The level at which the transaction is prepared to accept inconsistent data is called the isolation level. The isolation level is the degree to which a transaction must be isolated from other transactions. Low isolation levels can increase concurrency, but the cost is to reduce data correctness. On the contrary, high isolation levels can ensure data correctness, b

Tags: Body HTTP query Performance schema can be repeated without specifying If reproduced, please indicate the source of the blog: www.cnblogs.com/xinysu/, copyright belongs to the blog Garden su Home radish all. Hope you support! MySQL implements concurrency control through MVCC and locks, and in 4 isolation levels, read-write data and lock-in methods vary to meet different busin

the database based on certain conditions, transaction T2 inserts some records. When T1 reads data again based on the same conditions, it finds that there are more records. (This is also called phantom read) 1.3 read "dirty" Data Reading "dirty" data means that transaction T1 modifies a data and writes it back to the disk. After transaction T2 reads the same data

disappeared in secret. Transaction T1 a certain number of data records from the database, transaction T2 inserted some records, and when T1 again read the same conditions, more records were found. (This is also called Phantom Reading) 1.3 Read "Dirty" data Reading "Dirty" data means that a transaction T1 modify a data and write it back to disk.

This is the third time in my blog to repeat the isolation level of database transactions. This piece of content is a bit confusing. At that time, I understood it and I will forget it later. I think the trick to master the database transaction isolation level is to list the exceptions that occur during the transaction concurrency and the isolation level to prevent

When I encountered a problem during data insertion and update, I made a transaction: @ TransactionpublicvoidinsertOrUpdate (entity) {Objectosearch (entity); if (o! Null) update (entity); elseinsert (entity);} the pseudo code above is normal in a non-concurrent state. However, when concurrency occurs, multiple identical data records will be inserted. if you increase the isolation level for

11. Node. js asynchronous Process Control (sequential mode, concurrency mode, and limited concurrency Mode) In terms of basic syntax, Javascript is no different from most other C-derived languages. You may easily go from other languages to Javascript. Many users who transfer from other languages to Javascript may love and hate this language after a while, especia

want this to go into the 10, and eventually only one can move on.So this isif (Currentvalidsessionid = =-1){}The role of the. Once again, a request to the Atomic Protection queue is made, and only one can continue.A little thought:In fact, for a server with a frequency of N GHz, one memory is assigned to another memory data is the 1~4 instruction (average 2, two MOV operation), that is, 2/n ns time, not our hypothesis 1000ns (0.001ms). In fact, without atoms, we can

Concurrency Control for elasticsearch6 learning and elasticsearch6 concurrencyEnvironment: elasticsearch6.1.2 kibana6.1.2 Concurrency problems are everywhere1. Concurrency Control Based on _ version Before submitting data, check whether the version of the submitted data is c

inserts a row that satisfies the transaction 1 search rule. If transaction 1 executes the query again, a different series of rows is obtained.When you allow multiple applications to access the same data at the same time, you should maintain database consistency and data integrity. This is called "Concurrency" (concurrency