transaction and concurrency control

Nhibernate concurrency control"1" Pessimistic concurrency controlThe operation that is using the data, plus the lock, unlocks the resource when it is finished.Usage Scenario: Data is highly competitive and the cost of locking is lower than the cost of rolling back the transactionCons: Blocking, possibly deadlock"2" Optimistic

.10). Remove the exclusive lock and PENDING lock from all databases.It should be noted that in SQLite2, if multiple processes are reading data from the database, that is to say, there are always read operations in the database, that is, the database holds at least one shared lock at each time point, which will lead to no process being able to perform write operations, because the database cannot obtain the write lock when holding the read lock, we call this situation "Write hunger ". In SQLite3,

Add by Zhj: This article mainly talks about optimistic concurrency control, although optimistic concurrency control is less suitable for scenarios where concurrent write collisions are frequent, because this causes the transaction to roll back, requiring the user to retry th

sqlite2, if multiple processes are reading data from the database, that is to say, there are always read operations in the database, that is, the database holds at least one shared lock at each time point, which will lead to no process being able to perform write operations, because the database cannot obtain the write lock when holding the read lock, we call this situation "Write hunger ". In sqlite3, the pending lock is used to effectively avoid "Write hunger. When a process holds a pending l

OverviewIn order to improve concurrent MySQL to join the multi-version concurrency control, it saves the old version record in the shared table space, the transaction is not committed before the corresponding row record or lock restrictions, when the transaction committed after the corresponding record row in the cache

row locks, and the implementation of different storage engines is different. 5. Special NOTE: MySQL supports different levels of transaction isolation, the higher the isolation level, the greater the granularity of the lock, which is the more content of the lock. For example:consider the following situation, the transaction isolation level for A/b client is read-uncommitted, and the granularity of the lock

Multi-version concurrency control Most of MySQL's transactional storage engines do not implement simple row-level locks. Based on the consideration of improving concurrency performance, they generally implement multi-version concurrency control at the same time. MVCC can be

Tags: source code persistence database IsolationThis blog series has explored the Lmdb system architecture, MMAP mapping, b-tree operations, and so on, and this article will attempt to describe the implementation of transaction control in Lmdb. Basic characteristics of a transaction: Transactions are the basic unit of recovery and

Tags: Microsoft find increment repeatable by equals delete identity checkMVCC (multiple version Concurrent control) Multiple version concurrency control does not have a unified implementation standard. MVCC can be thought of as a variant of a row-level lock, but in many cases it avoids lock-up operations and is less expensive. Although the implementation mechanis

First, overview: In SQLite, the lock and concurrency control mechanisms are handled by the Pager_module module, such as acid (Atomic, consistent, Isolated, and durable). In a transaction that contains data modifications, the module ensures that all data modifications are committed or all are rolled back. At the same time, the module also provides memory cache fe

always transition from one consistent state to another;I:isolation, isolation; whether an action made by an office can be visible to other transactions before it is committed, and for the purpose of guaranteeing concurrent operations, there are multiple levels of isolation, which, if done rigorously, can lead to serial execution and lose the meaning of concurrent execution. There are four levels, the lowest isolation, the highest concurrency, the hig

performanceMVCC: Multi-version concurrency control, and transaction-level correlationTransaction ISOLATION LEVELSpecify the transaction ISOLATION level:Server Variables tx_isolation specified, the default is Repeatable-read , can be in GLOBAL and the SESSION level to setSET tx_isolation= "read-uncommittedread-committe

1. Introduction to data concurrency controlData concurrency control is a system used to process multiple modifications to persistent business objects at the same time point. When multiple users modify the state of the business object and try to persistently store it to the database concurrently, a mechanism is required to ensure that one user does not have a nega