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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, but cannot apply an exclusive lock until all shared locks are released. 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 add any type of lock to aunti
Optimistic locks and pessimistic locks, optimistic locks pessimistic locks Locking) This concept has been touched upon when we learned multithreading. In fact, the lock here and the concurrent lock processing in multithreading are a truth. They all violently classify resources as their own. Here, we use
In java learning, anonymous functions, constructor methods, constructor code blocks, calling constructor methods in constructor methods (small records in java learning), and java Constructor In java learning, calling constructor m
Update lost: New changes to overwrite first, the development of three ways to solve 1, raise the transaction level to the highest level transaction_serializable Both sides of the operation should raise the level; The query uses the shared lock; updates use the update lock; one query, one update, the shared lock and the update lock conflict; When both sides update the lock and a deadlock occurs, the program automatically rolls back one side of the operation to avoid the loss of the update 2, p
Parsing of file locks, mutex locks, and read/write locks in PHP programs ,. The use of file locks, mutex locks, and read/write locks in PHP programs is skillful in parsing. all file locks
Page Level: Engine BDB.Table-level: Engine MyISAM, which is interpreted as locking the entire table and reading at the same time.Row-level: Engine INNODB, locking a single row of records At the table level, the entire table is locked directly. During the lock period, other processes cannot perform write operations on the table. If you are writing a lock, other processes are not allowed to read it.Row-level, which only locks specified records, so that
In computer science, a lock is a synchronization mechanism used to forcibly restrict access to resources in the execution of multiple threads, which is used to guarantee the satisfaction of mutex requirements in concurrency control. In the DBMS, database locks can be divided into row-level locks (InnoDB engines), table-level locks (MyISAM engines), and page-leve
MySQL row-level lock, table-level lock, page-level lock details page-level: engine BDB. Table-level: engine MyISAM, which is interpreted as locking the entire table and reading at the same time. Row-level: engine INNODB, locking a single row of records At the table level, the entire table is locked directly. during the lock period, other processes cannot perform write operations on the table. If you are writing a lock, other processes are not allowed to read it.Row-level, which only
Page level: Engine BDB.Table level: Engine MyISAM, understood to lock the entire table, can be read at the same time, write notRow level: Engine INNODB, separate one-line record lock Table level, locking the entire table directly, and other processes cannot write to the table while you are locked out. If you are writing a lock, then the other processes are read and not allowedRow level, which locks only the specified record, so that other processes c
Overview of the LockWhy should I introduce a lock?Multiple users at the same timeThe concurrency of a database causes the following data inconsistencies:Missing updatesA,b two users read the same data and make changes, one of the user's changes to destroy the result of another change, such as booking systemDirty ReadA the user modified the data, then B users read out the data, but a user for some reason to cancel the modification of the data, data restore the original value, at this time the dat
This article mainly introduces the parsing of file locks, mutex locks, and read/write locks in PHP programs. it focuses on the examples used in the sync module and the pthreads module. For more information, see File lockThe full name is advisory file lock, which is mentioned in the book. Such locks are common. for exam
Object Lock (Method Lock), which is for an object that declares only one memory location of the object that identifies whether the object has a lock, all it locks the current object, and generally an object lock is a synchronized modification of a non-static member variable. or a non-static member method is synchronized, for object locks, different objects access the same synchronized modified method will n
MySQL row-level locks, table-level locks, page-level locks, mysql details Page Level: Engine BDB. Table-level: Engine MyISAM, which is interpreted as locking the entire table. It can be read at the same time but cannot be written at the row level. Engine INNODB locks a single row of records and directly
operation by acquiring a lock to do the same data operation, which is similar to the Java synchronized, so pessimistic lock takes more time. In addition to the optimistic lock corresponding to the pessimistic lock is implemented by the database itself, to use, we directly call the database of related statements can be.Here, the two other lock concepts involved in the pessimistic lock come out, and they are shared locks and exclusive
In computer science, a lock is a synchronization mechanism used to forcibly restrict access to resources when executing multiple threads, which is used to guarantee the satisfaction of mutex requirements in concurrency control.As described in the lock mechanism of the database, the database locks can be divided into row-level locks (InnoDB engines), table-level locks
The full name of the file lock is advisoryfilelock, which is mentioned in the book. Such locks are common. For example, after mysql and php-fpm are started, a pid file records the process id, which is the file lock. This lock prevents repeated running of a process. For example, when crontab is used, a task is executed every minute, The full name of the file lock is advisory file lock, which is mentioned in the book. Such
To avoid concurrency and prevent competition. The kernel provides a set of Synchronization Methods to protect shared data. Our focus is not to introduce the detailed usage of these methods, but to emphasize the difference between these methods and them.LinuxThe synchronization mechanism used can be said to have been continuously developed and improved since 2.0 to 2.6. From the initial atomic operation to the subsequent semaphores, from the large kernel lock to today's spin lock. Along with the
PHP file locks, shared locks, and exclusive locks. Note that there are two types of file locks: Shared locks and exclusive locks, that is, LOCK_SH and LOCK_EX) File locks are generally
Locking)During the implementation of business logic, data access needs to be exclusive. For example, end computing on the day of the Financial SystemProcessing, we want to process the data at a cut-off time point, rather than in the settlement process.(Several seconds or several hours), and the data changes again. In this case, we need to use some machinesThis mechanism ensures that the data is not modified by the outside world during an operation.Lock, that is, lock the target data we have sele
C ++ constructor copy constructor constructor of derived classes constructor of virtual inheritanceConstructor is a special method. It is mainly used to initialize an object when an object is created, that is, assigning an initial value to the object member variable. It is always used together with the new operator
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