devialet phantom

About innodb locks (record, gap, Next-Key lock) and innodbnext-key Record lock locks a single index record. Record lock always locks the index instead of the record itself, even if the table does not have any indexes, then innodb will create a hidden clustered primary key index in the background, and the lock is the hidden clustered primary key index. Therefore, when an SQL statement does not take any index, the X lock will be applied after each clustered index. This is similar to the table lock

the previous transaction, if the operation failed, was rolled back, and the last transaction read the error data, which resulted in dirty reads. Ii. non-repeatable Reads non-repeatable reading A transaction reads the same data multiple times, and when the transaction is not finished, another transaction also operates on the data, and the second transaction updates the data between the first transaction two reads, and then the first transaction is read two times before the data is different, whi

This paper is mainly for mysql/innodb concurrency control and lock technology to do a more in-depth analysis, and related to the important concepts, such as multi-version concurrency control (MVCC), dirty Read (dirty read), Phantom Read (Phantom Read), The four isolation levels (isolation level) are described in detail, and a detailed analysis of MySQL's locking is based on a simple example. The summary of

each transaction, an isolation level is specified that defines the degree of isolation between this transaction and other transactions. In MSSQL, there are 6 isolation levels, 4 regular isolation levels with 2 snapshot isolation levels: READ UNCOMMITTED, read Committed, read commmitted (row version), read repeattable, Snapshot and Read serializeble. Read commmitted (line version) may have less contact with snapshot, but it will still be explained. In MySQL, the default isolation level is RR,

Common consistency problems caused by concurrent operations in databases include: lost modifications, non-repeated reads, dirty reads, and Phantom reads (Phantom reads are often classified as non-repeated reads in some materials ). Here is an example of data inconsistency caused by concurrent operations. Consider an activity sequence in the aircraft ticket booking system Common consistency problems caused b

transfer money to the card before A's withdrawal. 4. Durability: after the transaction is completed, all updates to the database by the transaction will be saved to the database and cannot be rolled back. Conclusion: Atomicity is the foundation of transaction isolation, isolation and persistence are the means, and the ultimate goal is to maintain data consistency. Ii. Transaction concurrency 1. Dirty read: Transaction A reads the data updated by transaction B, and then B rolls back, then the d

read (repeable) This is the default transaction isolation level of MySQL. It ensures that multiple instances of the same transaction will see the same data rows when reading data concurrently. However, theoretically, this will lead to another tricky problem: phantom read ). In short, phantom read refers to when a user reads data in a certain range, another transaction inserts a new row in this range. When

Tags: database Isolation level transactionsFirst, what is the database?a database is a repository of data that is organized, stored, and managed according to a structure that is built on a computer's storage device. Second, why should the isolation mechanism be needed?Through the understanding of database definitions, in other words, the data is stored in a file in the form of a physical structure.The operation of the file is the operation of the IO stream, that is, the operation of reading and

transaction reads that uncommitted data cannot be read repeatedly: a transactionUpdate or deleteoperation, data inconsistency for another transaction two queries the Phantom reads: A transaction has been performed on the dataNew Action, the result of another transaction two queries is inconsistent. We see that non-repeatable reading is similar to Phantom reading, but in fact they are very different,non-rep

commits during the instance processing, so the same select may return different results. Repeatable Read (can be reread) This is the default transaction isolation level for MySQL, which ensures that multiple instances of the same transaction will see the same rows of data while concurrently reading the data. In theory, however, this can lead to another tricky problem: Phantom Reading (Phantom read). To pu

is selected, SQL Server will lock the entire table until the command or transaction ends. This prevents other processes from reading or modifying table data. Next, let's take a look at the transaction-level enumeration on the. net frameworks platform, which corresponds to the SQL event level. Namespace System. transactions {// Summary: // Specifies the isolation level of a transaction. public enum IsolationLevel {// Abstract: serialization isolation level, with the highest binding force. Pla

""}} "Node" Node3 "{fastname" domain01 "Pools" " Resource Disk "/data/sharedata/datasets" {Pools ""} Resource Scratchdisk "/data/scratch03" {Pools ""}} "node "Node4" {fastname "domain01" Pools "" Resource Disk "/data/sharedata/datasets" {Pools ""} Resource Scratchdisk "/data/scratch04" {Pools ""}}}/* end of entire config */ The config file contains 4 logical nodes, so when the job is run, DS creates 4 process parallel processes, and 4 logical nodes are assigned different scratchdisk. Thi

file. Binary log: records all operations performed to change the database.Relay logs and transaction logs. 1.4 conclusion1. redo log ensures the atomicity and durability of transactions (physical logs)2. the undo log ensures transaction consistency. the InnoDB MVCC (Multi-version concurrency control) is also implemented using the undo log (logical log ).3. The redo log contains checkpoints for efficient data recovery.4. Physical logs record the details of the modification page, and logical log

Tags: repeat TPS read-only hive based on the font Wikipedia transaction GPORead behavior is a condition that can be encountered when multiple transactions are executing concurrently, while reading data. Understanding them first helps you understand the meaning of each isolation level. These include dirty reads , non-repeatable reads , and Phantom reads . Dirty Read Dirty read also known as invalid data readout, refers to in the database access, transa

Tags: database Isolation level transactionsFirst, what is the database?a database is a repository of data that is organized, stored, and managed according to a structure that is built on a computer's storage device. Second, why should the isolation mechanism be needed?Through the understanding of database definitions, in other words, the data is stored in a file in the form of a physical structure.The operation of the file is the operation of the IO stream, that is, the operation of reading and

when necessary. This option works the same as setting HOLDLOCK on all tables in all SELECT statements within a transaction.Volatile data can is read but not modified, and no new data can addedDuring the transaction.Serializable = 0,//Summary: Repeatable read isolation levels, Phantom reads, locking all data used in queries to prevent other users from updating data, but other users can insert new phantom ro

Thoroughly understand the four isolation levels and transaction isolation levels of transactionsIntroduction In DBMS, transactions ensure that all or all of the operation sequences can be executed (Atomicity), from one State to another (consistency ). Because the transaction is persistent. Therefore, once a transaction is committed, the data can be persisted. Because the transaction is isolated, when multiple transactions process the same data at the same time, multiple transactions do not affec

exist. In most cases, a fully isolated transaction is seldom used. But a transaction that is not completely isolated brings up some of the following problems. Update lost (Lost update): Two transactions are attempting to update a row of data, causing the transaction to throw an unexpected exit, two transactions update is wasted. Dirty data (Dirty Read): Dirty reads occur if the second application uses the data that was modified by the first application, and this data is in an uncommitted state.

: Read uncommited,read committed,repeatable read,serializable, have a deep understanding. This article is not going to discuss how to define the meaning of these 4 isolation levels in database theory, but to tell you about how MYSQL/INNODB defines these 4 isolation levels. 4 isolation levels defined by MYSQL/INNODB: Read uncommited You can read UNCOMMITTED records. This isolation level is not used, ignored. Read committed (RC) Snapshot read ignored, this article is not considered. For the curren

. First you need to explain a few conceptual definitions related to isolation: (1) Dirty reading: Refers to the transaction read dirty data, the so-called dirty data, refers to the incorrect data, such as the transaction during the execution of the modification of a record, and then rollback, if the other transaction read the record in the middle of the modified value, dirty read. (2) Non-repeatable reads: A transaction reads the same existing record multiple times during execution, and the valu