mysql deadlock

Http://www.cnblogs.com/xrq730/p/4853713.htmlObjectiveDeadlocks write a separate article because it is a serious problem that must be brought to the attention of the individual. This is not an exaggeration of the risk of a deadlock, although the lock is usually held for a short time, the application as a commercial product may perform billions of times a day to acquire lock-and-release locks, as long as there is an error in these billions of operations

Deadlock and Activity degreeMany of the concurrency features and tools are discussed earlier, but most are related to locks. We use locks to ensure thread safety, but this can also cause problems. Lock sequence Deadlock (lock-ordering deadlock): A cyclic lock dependency occurs when multiple threads try to obtain multiple identical resources in different

conditions for deadlocks Mutex condition (Mutual Exclusion) : Resources cannot be shared and can only be used by one process. request and hold condition (holds and wait) : . no preemption condition (no pre-emption) : some system resources are not preempted, and when a process has obtained such a resource, the system cannot forcibly retract it, releasing the cyclic wait condition (Circular wait) : several processes form a ring chain, each occupying the next resource request

In computer science, deadlock is a naughty boy aroused by compete for resources. Even now,There isn't a valid method to deal with it. This is amazing. You know, we have already excellentScientists, not all of issues can fight with us so policyears. Fortunately, we can still do somethingBy sacrifle ice some system efficiency. Those methods can be divided into three categories:Preventation, avoidance, and detection. Let us examine them at the following

to read committed data changes. exclusive locks are held for transaction commit or rollback, but the shared locks are released immediately after the data is loaded into the memory.2. the read-only transaction can repeat the same query. No rows read by the transaction will be updated or deleted. The exclusive lock and shared lock will be held until the transaction ends, the query result set cannot be deleted or modified, but can be inserted.3. serializable read transactions can repeat the same q

The concept of first contact deadlock is the "Philosopher's meal" as described in the principle of operating system in a university course. In the operating system, a deadlock problem may occur because each process shares system resources. In the same Java multithreaded environment, there are also deadlock problems caused by resource sharing. When a set of Java t

Although a deadlock may occur while the process is running, a deadlock must have a certain condition, and the following four necessary conditions must exist for the deadlock to occur. 1 mutually exclusive conditions: refers to the process of allocating resources to the exclusive use, that is, for a period of time a resource is only occupied by a process. 　　If the

There are several processes in the operating system that execute concurrently, and they continuously apply, use, and release system resources, although the system's Communication agencies will control them, but there may be several processes waiting for each other to release resources Continue running, otherwise it will block the situation. At this time, without the help of external factors, no one can release resources, no one can solve In addition to the blocking state. Depending on the situat

I. Definition of deadlockmultithreading and multi-processes improve the utilization of system resources and improve the processing power of the system. However, concurrent execution also brings new problems-deadlocks. A deadlock is a deadlock (waiting for each other) of multiple threads due to competing resources, which cannot be pushed forward without external forces.Below we have some examples to illustra

When I execute a scheduler task in sql2005, try out: the transaction (process ID 86) and another process are deadlocked on the lock resource, and have been selected as the deadlock victim. Run the transaction again. After finding the information on the Internet, I found that the table was closed when I first accessed the table while executing the scheduled task at the same time, and the second was also accessed, this error occurs, so when you think of

Label:This article from: http://blog.sina.com.cn/s/blog_6f33ee7901018nsd.html Database blocking and deadlock often occur in the process of program development, how to avoid it? Below through demo simple simulation, the database is blocked and deadlock phenomenon:One, database blocking:Database blocking phenomenon: The first connection occupies a resource that is not released, and the second connection need

Background: For the deadlock problem, people tend to think of some very slow, white-page phenomenon, if the test environment (I have a real test environment to talk about the same problem) you will restart the PHP php-fpm process to find out again, after a period of similar problems, you will look at the log, You will find that there are a lot of logs that are "Max execution timeout of seconds exceeded", you will find that this may be caused by some P

Deadlock has actually been mentioned in semaphores. When a process wants to apply for resource A, has resource B, and another process wants to apply for resource B, but has resource a, a deadlock will occur.Semaphores are a certain number of resources. There are many resources, such as memory space, CPU cycle, and I/O devices. Each resource has a certain number of resource instances.Resources are the same a