transaction and concurrency control

, Damage to the Transaction2 results, causing Transaction2 to violate acid.The fundamental reason why the ideal MVCC is difficult to achieve is the attempt to replace the two-paragraph submission with optimistic locking. Two rows of data are modified, but to ensure consistency, there is no difference between modifying data in two distributed systems, and two commits are the only means of ensuring consistency in this scenario at this time. Two paragraph of the nature of the submission is locked,

control only includes two operations: start transaction and end transaction.SET transaction: used to set the attributes of the next transaction to be executed.Start transaction: Start transaction execution.Ser constrains: used to

previous read results.3) Phantom read: Transaction T1 after reading some data records from the database according to certain conditions, the transaction T2 inserts some records, and when T1 again reads the data in the same condition, it finds some more records.concurrency control1) The concurrency control of the datab

Why locks (concurrency control) are required. In a multiuser environment, multiple users may update the same record at the same time, which can create a conflict. This is the famous concurrency problem. Typical conflicts are:(1) Missing update: One transaction update overwrites the update result of other transactions

timeouts and lock contention issues.Phantom Read (Phantom Read): When a transaction reads a range of records, another transaction inserts a new record in that range, and when the previous transaction reads the records in that range again, a magic line (Phantom row) is generated.1.3.2 DeadlockA deadlock is a vicious cycle in which two or more transactions occupy

problemA concurrency control problem with a distributed system has been encountered in recent projects. The problem can be abstracted as: a distributed system consists of a data center D and a number of business processing centers l1,l2 ... LN is essentially a Key-value store, which provides an HTTP protocol-based CRUD operation interface externally. The business logic of L can be abstracted into the follow

When multiple transactions are concurrently executed in the database, data consistency may be damaged. It is necessary for the system to control the interaction between transactions, which is achieved through one of multiple mechanisms of the concurrency control mechanism. To prevent the transaction from getting star

: one transaction Reads the updated data committed by another transaction.Second lost updates problem (Second type of loss update): this is a special case in non-repeatable read. One Transaction overwrites the updated data committed by another transaction.Transaction isolation level and possible problemsThe key to ensuring the accuracy of concurrent transactions is to serialize the scheduling of conflicting

Data Distribution is usually used in high-performance computing (HPC. There are two main data distribution topologies: Replication and partitioning. In a Data Replication environment, a data item usually has several copies, but data consistency should be ensured to a certain extent, so that the end user can only have one copy of data globally. The biggest challenge to using data replication is to make a correct balance between data consistency and Performance Based on business needs. To achieve

Tags: new version application decision to prevent algorithm deadlock concurrency control line statusWhen multiple transactions are executed concurrently in the database, the consistency of the data may not be maintained. It is necessary for the system to control the interaction between the various transactions, which is achieved through a mechanism called

some data records from the database according to certain conditions, the transaction T2 inserts some records, and when T1 reads the data again by the same conditions, it finds some more records.concurrency control1) The concurrency control of the database is to dispatch the concurrency operation in the correct way, so

-repeatable read REPEATABLE Read REPEATABLE read, every time you see the same data, the data is modified to see the latest data, will produce a phantom read (default setting) Setializabile uncommitted read transaction blocking modification transaction, serial execution, poor concurrency MVCC: Multi-version

MySQL MVCC (Multi-version concurrency control) and mysqlmvccOverview To improve the concurrency of MySQL, a multi-version concurrency control is added. It stores the old record in the shared tablespace, and the corresponding row records are still subject to the lock before t

results.RepeatableRead (can be reread)This is the default transaction isolation level for MySQL, which ensures that multiple instances of the same transaction will see the same rows of data while concurrently reading the data. In theory, however, this can lead to another tricky problem: Phantom Reading (Phantom read). Simply put, the Phantom read worth when a user reads a range of data rows, another

Tags: 9.png queue diagnostics Request other multiple SRC run basicThe 11th Chapter concurrency control This paper introduces the problems that concurrency can cause data inconsistency, explains the basic concepts of concurrency control and the most common blocking technique

--Rolls back the transaction and cancels all previous SQL.Mode two: There is an autocommit variable in the database, via show variables like '%commit% '-----The autocommit value is on, which indicates that transaction autocommit is turned on.You can set Autocommint = Off (set autocommint=0) to turn off autocommit, and the SQL statement entered will not be automatically submitted, requiring a manual roolback