Http://www.infoq.com/cn/articles/java-memory-model-5 deep understanding of the Java Memory Model (v)--lock
Http://www.ibm.com/developerworks/cn/java/j-jtp10264/Java Theory and Practice: a more flexible and scalable locking mechanism in JDK 5.0
http://blog.csdn.net/ghsau/article/details/7481142
1, Synchronized
Declaring a block of code as synchronized has two important consequences, usually the code has atomicity (atomicity) and visibility (visibilit
The previous article introduces the lock that protects memory structure or variable in MySQL source code, and here we begin to introduce the table lock in MySQL transaction.Note 1: On the implementation of the table lock, the structure of "mutex+condition+queue" is used to implement the table lock function of concurren
In addition to Spinlock, the Linux kernel also has a spin lock called arch_rwlock_t. Its header file is Qrwlock.h, contained in Spinlock.h, which is called "Queue read/write lock" in the header file. This lock implements a read-write lock using only two member variables. A spinlock, and a shaping
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
With the development of the Internet, more and more Internet enterprises are confronted with the concurrency security problems caused by the expansion of user volume. This paper mainly introduces several kinds of locking mechanisms common in Java concurrency.1. Bias Lock The bias lock is a mechanism of lock optimization proposed by JDK1.6. The core idea is that i
5000 employees have 10 people, transaction a read all wages for 5000 of the number of 10 people.
At this time
Transaction B Inserts a record with a salary of 5000.
This is, transaction a reads the employee with a payroll of 5000 again, and records 11 people. This creates a phantom read.
4. Reminders
The key to non-repeatable reading is to modify:
The same condition that you read the data, read it again and find that the value is different
The focus of Phantom reading is to add or delete:
Th
Tags: read-only and tle sele generation process external HTTPS openNote: This article is reproduced from http://www.hollischuang.com/archives/934As described in the lock mechanism of a database, the task of concurrency control in a database management system (DBMS) is to ensure that the same data in the database is accessed simultaneously without disrupting the isolation and uniformity of the transaction and the consistency of the database.Optimistic
With the frontline synchronization only know the Synchronize keyword, then know that there is a lock, why also have a lock to achieve synchronization? Synchronized's limitations occupy the lock thread waiting for IO or other reasons to be blocked, without releasing the lock, Read and read can also conflict when other t
Tags: Oracle databaseA DML lock, also called a data lock, is used to ensure that data is complete when multiuser data is manipulated. DML locks prevent conflicting DML and DDL operations from occurring at the same time.DML locks have row locks,tx and table locks (table Locks,tm), and the corresponding locks are automatically requested by different DML operations.Row loc
In the database lock mechanism, the task of concurrency control in a database management system (DBMS) is to ensure that multiple transactions simultaneously access the same data in the database without disrupting the isolation and uniformity of the transaction and the consistency of the database.
Optimistic concurrency control (optimistic lock) and pessimistic concurrency control (pessimistic
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
When InnoDB determines whether a row lock is in conflict, in addition to the most basic is/ix/s/x lock collision judgment, InnoDB also subdivides the lock into the following seed types:
Record Lock (RK)Record locks, lock only one row of index records
Gap
The lock mechanism is an important feature of a database that is different from the file system and an effective way to manage concurrent access. MySQL locks include table-level locks, page-level locks, and row-level locks. Table-level locks are the most granular locks in MySQL. They are easy to implement and consume less resources. They are supported by most MySQL engines. The most commonly used MYISAM and INNODB support table-level locks.
The
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,
A 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 lock usage mode. After some improvement, we can basically achieve
GMB
Network Adapter working at full speed. In
After the performance was up to standard, I was wondering if I could use a more lightweight
Pessimistic lock and optimistic lock in hibernate
Locking)During the implementation of business logic, data access needs to be exclusive. For example, in the daily final computing process of the financial system, we want to process the data at a cut-off time point instead of the settlement process (which may be several seconds, or several hours), and the data changes again. At this point, we need to use som
Note: This article is reproduced from http://www.hollischuang.com/archives/934As described in the lock mechanism of a database, the task of concurrency control in a database management system (DBMS) is to ensure that the same data in the database is accessed simultaneously without disrupting the isolation and uniformity of the transaction and the consistency of the database.Optimistic concurrency control (optimistic
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
Tag: Code member jdk1.7 read illegal boolean return port OwnerRelease Fair Lock (based on jdk1.7.0_40)1. Unlock ()Unlock () implemented in Reentrantlock.java, the source code is as follows: Public void unlock () { sync.release (1);}Description :Unlock () is an unlock function, which is implemented by Aqs's release () function.Here, the meaning of "1" is the same as the "Get Lock function acquire (1)", wh
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