Types and Research of Oracle Database locks, oracle Database locks
A database is a shared resource used by multiple users. When multiple users access data concurrently, multiple transactions can access the same data simultaneously in the database. If concurrent operations are not controlled, incorrect data may be read and stored, compromising Database Consistency.
There are two basic lock types in the data
Spin locks and mutually exclusive locks are two important concepts in multi-thread programming. They can all be used to lock some shared resources to prevent concurrent questions that affect data consistency. But there are indeed differences between them. What are these differences?1 Theory
Theoretically, when a thread tries to obtain a locked mutually exclusive lock, the operation fails and the thread goes
Describe the principles and three implementation methods of distributed locks in detail, and describe the principles of locks.
Currently, almost all large websites and applications are deployed in a distributed manner. Data Consistency in Distributed scenarios has always been an important topic. The distributed CAP theory tells us that "No distributed system can meet both Consistency, Availability, and Part
FCNTL has a powerful capability to copy an existing descriptor, get/Set file descriptor tags, get/Set file status tags, get/Set asynchronous I/O ownership, get/set record locks.
When multiple users work together to manipulate a file, Linux usually uses the method of locking the file to avoid competing status with shared resources.
There are two types of fcntl file locks: Recommended
The locking mechanism used by the MyISAM storage engine is fully implemented by the table-level locking mechanism provided by MySQL.
MySQL has two types of table-level locks: Write locks and read locks.
For write locks, MySQL uses the following table locking method:* If there is no lock in the table, put a write lock o
The pessimistic lock, as its name implies, is very pessimistic. Every time you get the data, you think someone else will modify it. So every time you get the data, you will lock it, in this way, others will block the data until it gets the lock. In traditional relational databases, many of these locks are used, such as row locks, table locks, read
Two File locks in Linux and two file locks in Linux
A file lock is a file read/write mechanism that allows only one process to access one file at any specific time. Using this mechanism can make the process of reading and writing a single file more secure.
In this article, we will explore different types of File locks in Linux and use the example program to under
Implement distributed locks Based on Redis and distributed locks Based on Redis
BackgroundIn many Internet product applications, some scenarios require locking, such as seckilling, global incremental ID, and floor generation. Most solutions are implemented based on databases. Redis adopts the single-process and single-thread mode and uses the queue mode to convert concurrent access to serial access. In addi
Lightweight locks
The JDK1.6 appeared. It is not a substitute for a heavyweight lock, which is meant to reduce the performance consumption of traditional heavyweight locks using operating system mutexes without multiple threading competition. Hotspot the Run-time data of the virtual machine Object Header object itself
such as: hash (hashcode), GC generational age (generational GC), this part of the data in
lock is used.
Multiple locks can be directly processed in parallel based on different imported keys, similar to the row-level locks of Innodb.
Use:
$ Lock = new CacheLock ('key _ name ');
$ Lock-> lock ();
// Logic here
$ Lock-> unlock ();
// Note that the write permission is required for the path of the file lock.
The specific classes are as follows:
The code is as follows:
/**
* CacheLock process loc
Oracle row-level locks and table-level locks. If the row record has been locked, wait for 5 seconds for updates. If the row record is unlocked within these 5 seconds, the query result is returned, if 5 seconds
Oracle row-level locks and table-level locks. If the row record has been locked, wait for 5 seconds for update
There is a lock mechanism in Mysql. It is generally used in multi-user concurrent operations. pessimistic locks can prevent the loss of updates and non-repeated read concurrency problems, but they will affect the concurrency performance. So I 'd like to know if Mysql's pessimistic lock will be used in the project program. Thank you for your reference...
There is a lock mechanism in Mysql. It is generally used in multi-user concurrent operations. p
Understanding mysql locks (2) Table-level locks the MyISAM storage engine uses a locking mechanism completely implemented by the table-level locks provided by MySQL. Mysql has two types of table-level locks: write locks and read locks
Java. util. concurrent. locks. ReentrantLock class usage, concurrent. locksThe lock class is implemented as follows: Explanation of the ReentrantLock interface method:
The lock () method is used to obtain the lock object. If the lock is not obtained, the lock is always obtained.
Trylock (): A boolean value. It indicates whether the lock is obtained. If the lock is not obtained, false is returned. If the lock is obtained, true is returned.
TryLock (lon
Shared lock (s lock ):
If transaction t adds a shared lock to data a, other transactions can only add a shared lock to data a and cannot apply exclusive locks. Transactions authorized to share locks can only read data and cannot modify data.
Exclusive lock (x lock ):
If transaction t adds an exclusive lock to data a, other transactions cannot block aplus any type. Transactions authorized to exclusive
Detailed description of pessimistic locks and optimistic locks in the database; Detailed description of the Database
There are two types of locks in data: Pessimistic locks and optimistic locks, as well as table-level locks and r
Note: This article is reproduced from http://www.hollischuang.com/archives/923Row-level locks, table-level locks, page-level locks are described in MySQL, row-level locks are the most granular lock in MySQL, and row-level locks can significantly reduce database operation con
Note: This article is reproduced from http://www.hollischuang.com/archives/923Row-level locks, table-level locks, page-level locks are described in MySQL, row-level locks are the most granular lock in MySQL, and row-level locks can significantly reduce database operation con
Java lock locks specific objects and javalock locks
Since lock does not lock a specific object, how can we achieve the same effect as synchronized synchronization blocks?
Answer: assign a lock to each object needing to be locked.
Example:
List
Efficiency Comparison (MACHINE: macOs10.12.5, i5 processor, 8 GB memory)
// Thread_count synchronized lock// 10 1-2 ms 2-3 ms// 100 8-12 ms 7-12 ms// 1000 68-9
pthread_cond_wait, this is done in order to take control of the mutex back to the call Pthread_cond_ The thread of wait (that is, thread1). Tidy up the basic timing: 1 Lock 1 1 unlock (in 2lock221 Lock(in1 unlock(2) in the process of using a condition variable, it is usually added with the value of a bool or int test_cond. One thing to note here is that it is important to change the test_cond before signal to ensure that the wait thread is woken up to be able to get the correct test_cond valu
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