lock computer

Java Day one article June 21 First introduce some optimistic lock and pessimistic lock:Pessimistic lock: Always assume the worst case, every time to take the data when they think others will change, so every time when the data are locked, so that other people want to take this data will block until it gets the lock. Traditional relational database in the use of a

deadlock free, because MyISAM always gets all the locks needed at once, either all satisfied, or waits, so there is no deadlock. However, in InnoDB, except for a single SQL-composed transaction, the lock is progressively obtained, which determines that InnoDB deadlock is possible. After a deadlock occurs, InnoDB is typically automatically detected, and a transaction is freed and returned, and the other transaction is locked and the transaction cont

First introduce some optimistic lock and pessimistic lock:Pessimistic lock: Always assume the worst case, every time to take the data when they think others will change, so every time when the data are locked, so that other people want to take this data will block until it gets the lock. Traditional relational database in the use of a lot of this locking mechanis

First of all explain: Method lock and Object lock is said to be a thing, that is, only method lock or object lock and class lock two kinds of locks The author uses the easy language to explain the complex technology so thoroughly, learn, spread. Original address: http://zhh

One: Java multi-threaded mutex, and Java multithreading introduce the reason for the bias lock and lightweight lock? --->synchronized of the weight of the lock, that is, when the thread runs to the code block, the program's running level from the user state to the kernel state, to suspend all the threads, so that the CPU through the operating system instructions

Java Object Header and monitorJava object headers are the basis for implementing synchronized lock objects, and the lock objects used by synchronized are stored in the Java object header.The object header contains two parts: Mark Word and Class Metadata AddressWhere Mark Word stores the object's hashcode, generational age, lock tag bit, and so on by default the f

Reentrantlock is a reentrant lock that can support a thread to repeatedly lock resources, and he also supports fair locking and unequal locking. The Synchronized keyword also implicitly supports re-enter, such as a recursive method of synchronized modification, when the method executes, The execution thread can still obtain the lock multiple times after acquiring

Synchronized is a mutual exclusion lock;Lock is more extensive and includes read/write locksRead/write Lock features:1) Multiple readers can read at the same time2) The writer must be mutually exclusive (only one writer is allowed to write, nor does the reader write at the same time)3) The writer takes precedence over the reader (once the writer is written, the s

the lock concept in MySQLDifferent storage engines in MySQL support different locking mechanisms. For example, the MyISAM and memory storage engine with table-level locks, bdb with a page lock, also supports table-level locks, InnoDB storage engine supports both row-level locks, table-level locks, by default, row-level locks.The MYSQL3 lock features are as follow

　In the development of distributed cluster system, the thread lock is often not able to support the use of all scenarios, and a new technology scheme distributed lock must be introduced.　　thread Lock: Everyone is not unfamiliar, mainly used to give methods, code block lock. When a method or block of code uses a

From: http://www.blogjava.net/xylz/archive/2010/07/07/325410.html Next, this article starts with lock. Lock/unlock. In special cases, all programs, APIs, and documents are based on JDK 6.0. Public void java. util. Concurrent. locks. reentrantlock. Lock () Obtain the lock. If the

Recently encountered multithreading problem, originally only used synchronized method lock, for which the object lock and class lock understanding, but not carefully studied. So go back and check the relevant data for collation. Basic Knowledge First the introduction of object lock (also called method

Are class locks and object locks conflicting? are object locks and private locks conflicting? Explained by an instance. I. Relevant agreement To clarify the description of the following article, first of all the relevant definitions of the lock involved in this article are as follows: 1. Class Lock: A static and synchronized lock is added to the method in the

4. Lock-Performance Comparison and Analysis of lock-free programming and lock programming-Performance ComparisonA recently maintained network server encountered performance problems, so it made major changes to the original program framework. Most of the changes are the thread working mode and data transmission mode. The final result is to change the

Tags: check log eric Share blog exclusive pessimistic lock good usesql-optimistic lock, pessimistic lock in the concurrency Every time you write a blog, the first sentence is this: the programmer is very hard, in addition to writing procedures, but also to write a blog! Of course, hope that the future day, a boss see this blog, to your programmer staff pay bar! B

MySQL database lock mechanism-MyISAM engine table lock and InnoDB row lockLock concept in MySQL Different storage engines in Mysql support different lock mechanisms. For example, the MyISAM and MEMORY storage engines use table-level locks. BDB uses page locks and table-level locks. the InnoDB Storage engine supports row-level locks and table-level locks, row-leve

Every time you write a blog, the first sentence is this: the programmer is very hard, in addition to writing procedures, but also to write a blog! Of course, hope that the future day, a boss see this blog, to your programmer staff pay bar! Because the programmer's world is silent except bitter force. Most of the programmers in my eyes do not love to talk, silently bear the great pressure of programming, in addition to technical exchanges, they do not want to be good at communicating with others,

Oracle lock 1: DML lock, oracle lock 1dmlDML lock, also known as data lock, is used to ensure data integrity when multiple users operate on data. DML lock prevents conflicting DML and DDL operations at the same time. DML Locks inc

SNWHERE se.statics# = sn.statics#and NAME like '%cpu used by this session% 'and Se.sid = Ss.sidand ss.status = ' ACTIVE 'And Ss.username is not NULLORDER by VALUE DESC;--Get current session ID, process ID, client ID, etc.SELECT B.sid, B.serial#,a.spid ProcessID, b.process clientpidFrom V$process A, v$session bWHERE a.addr = b.paddr and B.audsid = USERENV (' SessionID ');--Query and display the actual Oracle link in the viewSELECT Osuser,username,machine,programFrom V$sessionORDER by Osuser;--Qu

1.1.1.three write lock downgrade for read-write lock applicationReentrantreadwritelock also features write-lock demotion, which has some relationship to reentrant sex. (1) you can downgrade to read lock when holding a write lock. (2) You cannot upgrade to a write