![]() Therefore, all DBMS, including PostgreSQL, track locks automatically. If a deadlock occured, the involved transactions can do nothing but wait infinitely. If a graph contains a cycle (from a vertex, we can get to itself in a walk along arrows), this is a deadlock.Ī deadlock can certainly occur not only for two transactions, but for any larger number of them. To do this, we remove specific resources, leave only transactions and indicate which transaction waits for which other. To visualize a deadlock, it is convenient to build the wait-for graph. ![]() The figure on the left below illustrates this: solid-line arrows indicate acquired resources, while dashed-line arrows show attempts to acquire a resource that is already in use. It occurs when one transaction tries to acquire a resource that is already in use by another transaction, while the second transaction tries to acquire a resource that is in use by the first. When using locks, we can confront a deadlock. We'll start with deadlocks (actually, I planned to discuss them last time, but that article was excessively long in itself), then briefly review object-level locks left and finally discuss predicate locks. DDL operation table in Mysql, modify field type, length, add and delete columns, etc.We've already discussed some object-level locks (specifically, relation-level locks), as well as row-level locks with their connection to object-level locks and also explored wait queues, which are not always fair.sql security injection problem solution.go moduleized import calls the local module tidy.The four characteristics of database transactions and isolation level, take you to see fully.JVM runtime memory space detailed - program counter.go sync.WaitGroup main coroutine waits for multiple sub-coroutines sync.Mutex locks atomic operation atomic.How to generate serial number based on date + number.Use these 19 MySQL optimizations skillfully to increase the efficiency by at least 3 times.Gao Kunlun is strengthened under high numbers.184 pages and 100,000 words of smart city public service middle office: business and data middle office construction plan.Gao Kunlun is strengthened in high mathematics.For the memory visibility of data, flash may be repeated back and forth in the thread working memory and main memory, withto performance overhead. ![]() In the case of multi-thread cooperation, for thread safety, the compiler or CPU instruction reordering (such as violate) may be prohibited. Ps: In order to avoid frequent context switching, the thread scheduler will set the minimum execution time for the scheduled thread. This is the cache invalidation caused by thread scheduling. The cached content just disappears and has to be recalculated. The context switch will suspend the current thread and find the next code to be resumed.If the task to be executed is relatively simple, the overhead of thread scheduling may be larger than the actual execution content.Īfter the current task caches the content, it switches to another thread, and then switches back. The operating system will allocate a time slice to each thread according to a certain scheduling algorithm. Slow server response, low throughput, and excessive memory usage are performance issues. Third, why does multithreading cause performance problems? What is a performance issue: Which scenarios require extra attention to thread safety issues?ġ) When accessing shared variables or caches: for example, two threads perform i++ operations on global variables at the same time Ģ) Timing-dependent operations: such as double-checking during lazy creation of singleton objects ģ) There is a binding relationship between different data: such as IP and port number, they need to be bound together to become an atomic operation Ĥ) Access to a thread-unsafe object: such as ArrayList. Hunger: If a thread's priority is set very low (1 is the lowest), it can't get CPU resources and cannot run.Ģ. Livelock: For example, an error message in the message queue is repeatedly placed at the head of the queue for execution When multiple threads access an object, there is no need to consider the problem of simultaneous writing or parallel reading and writing, and no additional synchronization operations are required, then the object is said to be thread-safe.ġ) Error in running result: if two threads access the shared variable i at the same time, perform 1000 i++ operations without synchronization Ģ) Thread safety issues caused by release and initialization: If the child thread has not initialized an object, the main thread will access it and get null ĭeadlock: if two threads get each other's locks and are unwilling to release What are the three types of thread safety issues? What is thread safety:
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |