kiosk lock

Locks are a tool for concurrent shared data, ensuring consistency, and many implementations (such as synchronized and Reentrantlock, etc.) on the Java platform. These have been written to provide the lock to facilitate our development, but the specific nature of the lock and the type is rarely mentioned. This series of articles will analyze the common lock names

Record LockA single index record is locked, the record lock is always indexed, not the records themselves, even if there is no index on the table, then InnoDB creates a hidden clustered primary key index in the background, so the hidden clustered primary key index is locked. So when an SQL does not take any indexes, it will add an X lock behind each clustered index, similar to a table

In Java multithreading, you can use the keyword synchronized to implement a mutex between threads. After JDK1.5, a thread concurrency library java.util.concurrent is provided to manipulate multiple threads, including java.util.concurrent.atomic and Java.util.concurrent.lock. Atomic can realize the atomic operation of data or variable, and lock can achieve thread mutual exclusion, can realize read-write lock

Turn InnoDB row-level locksInnoDB Row-level locksCategory: Database 2013-03-13 16:40 1745 people read comments (0) favorite reports Nnodb lock mode and lock methodInnoDB implements the following two types of row locks.? Shared Lock (S): Allows a transaction to read one line, preventing other transactions from acquiring an exclusive

Pessimistic lock (pessimistic lock), as the name implies, is very pessimistic, every time to take the data when they think others will change, so every time when the data are locked, so that others want to take this data will block until it gets the lock. Traditional relational database in the use of a lot of this locking mechanism, such as row locks, table locks

Why do I need a lock (concurrency control)? 　　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: missing updates : Updates for one transaction overwrite the update results of other transactions, which is called update loss. For example: User A changes the value from 6 to 2, and User B changes the value from 2 to 6,

Preface: Read Song Sang's article "An accidental x lock does not block the problem", combined with my test, explain my use of the X lock in select will hold to the end of the transaction error;Details not much to say, see Song Sang's "An accidental x lock does not block the problem" and "Lost shared lock", the select+x

Suppose a user (assuming a) issues the following statement to update a record: Sql> Update Employees set last_name= ' Hansijie ' where employee_id=100; Example above, at which point a user has issued an SQL statement that updates the record for employee_id 100. When a has not yet been submitted, another user D issues the following statement: sql> drop table employees; Because user A has not committed a transaction yet, the transaction has not ended, and other users cannot delete the table,

The thread in Python is the native thread of the operating system, and the Python virtual machine uses a global interpreter lock (Global interpreter Lock) to mutex the use of the Python virtual machine. In order to support multithreading mechanism, a basic requirement is to implement the mutual exclusion of different threads to access shared resources, so the Gil is introduced.GIL: After one thread has acce

1. Sync Lock (Lock)Data disturbances occur when individual threads need access to a common resourceFor example:1 Import Threading,time2 def Sub ():3 GlobalNum #对全局变量进行操作4 5temp=Num6Time.sleep (0.001) #模拟线程执行中出现I/o delay, etc.7num=temp-1#所有线程对全局变量进行减一8 9Time.sleep (1)Ten Onenum= - AL=[] - - forIinchRange -): theT=threading. Thread (target=sub,args=()) - T.start () - l.append (t) - + forObjinchL: - O

SQL Lock table Reconciliation lock MySQL Tutorial statement For MySQL, there are three types of lock levels: page level, table level, row level The typical page-level representative engine is BDB.The typical representative engine for the table level is myisam,memory and ISAM, a long time ago.The typical line-level representative engine is InnoDB. -the most use

The comparison between optimistic lock and pessimistic lock: Category Realize Characteristics Risk Pessimistic lock Rely on the lock mechanism of database layer Exclusive Nature The large overhead of database performance is often unsustainable, especially for