devialet phantom

(nonrepeatable Read) transaction T1 reads a row of records, and the transaction T2 modifies the row of records that the T1 just read. The T1 then reads the line again and finds that it differs from the result just read. This is referred to as "non-repeatable" reading because the row record that T1 originally read has changed. The Phantom Read (Phantom Read) transaction T1 reads a result set returned by

transaction may have new commits during the instance processing, so the same select may return different results.Repeatable Read ( can be reread ) [ri ' Pi:tebl] 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 (

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 put it simply, Phantom reads when a user

this case, non-repeated read occurs. (A transaction rereads data it has previusy read and finds that another committed transaction has modified or deeted the data .) phantom read: The same query is performed multiple times in the same transaction. Because of the insert operations performed by other commit firms, different result sets are returned each time. In this case, a phantom read occurs. (A transacti

the consistency of each data read/write operation. The standard SQL92 Specification defines four isolation levels and three Phenomena (Phenomena) to be banned ). The higher the isolation level, the stronger the guarantee of data consistency, but the worse the database concurrency. Problems caused by concurrent database operations include: 1. Dirty read (Dirty read ). Transaction A reads data that has not been committed in transaction B. If transaction B rolls back, A reads the wrong data. 2. Un

same transaction may have a new commit during the processing of this instance, so the same select may return different results. Repeatable 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,

context.Isolation levelThe second aspect of a declarative transaction is the isolation level. The isolation level defines the degree to which a transaction may be affected by other concurrent transaction activity activities. Another way to think about the isolation level of a transaction is to think of it as the selfish degree to which the transaction deals with the data.In a typical application, multiple transactions run concurrently, often manipulating the same data to complete their work. Co

the data, the average age of students is (40 + 50)/2 = 45. The average age calculated by user B is 25 or 45, which is acceptable. However, in the preceding example, the average age 35 calculated by user B is an error value that has never occurred in the system.-Phantom read): The same query is performed multiple times in the same transaction. Although the query conditions are the same for the insert operations performed by other commit firms, the ret

the transaction commits to release, read with a shared lock, read release transaction 1 read data with a shared lock (so that in the process of reading data in transaction 1, other transactions will not modify the data), do not allow any transaction operation of the data, can only read, After 1, if there is an update operation, it will be converted to an exclusive lock, other transactions are not entitled to participate in the read and write, which prevents dirty read problems. However, when th

Tags: csharp sha snapshot Microsoft sans tween release document www.Reference Documentation:Https://docs.microsoft.com/zh-cn/sql/t-sql/statements/set-transaction-isolation-level-transact-sqlhttps://msdn.microsoft.com/zh-cn/library/jj856598 (v=sql.120). aspxOne, the transaction isolation level controls the following behavior of the transaction:Whether the lock is occupied while reading the data and the type of lock requested.The time that the read lock was occupied.Read operations that refer to r

additional lock operations are allowed Four isolation levels for transactionsIn the database operation, in order to effectively guarantee the correctness of the concurrent read data, the transaction isolation level is proposed. Database locks are also available to build these levels. READ UNCOMMITTED: Allow dirty reads, which may read data that has not been committed in other sessions Commit read: Only the data that has been committed can

called "Dirty reading". non-repeatable read (non-repeatable Reads): A transaction is reading some data has changed, or some records have been deleted! This phenomenon is called "non-repeatable reading". Phantom Read (Phantom Reads): A transaction re-reads the previously retrieved data in the same query condition, but finds that other transactions have inserted new data that satisfies its query crit

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 put it simply, Phantom reads when a user

(Durability): After the transaction is complete, all updates to the database are saved to the database and cannot be rolled back.Second, the concurrency problem of the transaction1. Dirty read: Transaction A reads the updated data of transaction B, then B rolls back the operation, then a reads the data is dirty data2. Non-repeatable READ: Transaction a reads the same data multiple times, transaction B updates and commits the data during transaction a multiple reads, resulting in inconsistent re

read.Then T1 again, discovering that the record was different from the first read.DeclareBeginDbms_output.put_line (' first reading: ');For RS in (SELECT * from all_objects) loopIf Rs.object_name= ' EMP ' thenFor rs1 in (SELECT * from emp) loopDbms_output.put_line (' Ename= ' | | rs1.ename| | ' sal= ' | | Rs1.sal);End Loop;End If;End Loop;Dbms_output.put_line (' second reading: ');For RS in (SELECT * from all_objects) loopIf Rs.object_name= ' EMP ' thenFor rs1 in (SELECT * from emp) loopDbms_ou

transaction:ActivitiesPartial submissionsFailedStopSubmitA transaction must be in one of the top five states at a time, and the transformation between the state of the transaction is as follows: Issues caused by transaction concurrencyDirty Reads (drity read): A transaction has updated one copy of the data, another transaction reads the same data at this time, for some reason, the previous rollback operation, the latter will read the data is not correct.Non-repeatable read (non-repeatable

to solve the problem of phantom reading in repeatable reading mode, and how to solve the Phantom reading with the demonstration of Phantom reading and Gap lock. For this piece, give a couple of definitions first.Snapshot read:Simple select operation, no lock in share mode or for update, snapshot read does not add any locks, and because of the consistency of MySQ

READ (repeatable Read)The default isolation level of MySQL, which guarantees that the same record is read multiple times in the same thing, but this can be a phantom read (Phantom read) problem, which is when a transaction reads a record in a range, another transaction inserts a new record within that range. When the previous transaction reads the range record again, the

Tags: des style blog http io ar color OS useSource: SQL Drip 9-sql transactions in server and built-in transactions in SSISWe can include the entire package in SSIS in a single transaction, but what if a table needs to be locked in the process of the package execution? SSIS built-in transactions can solve this problem. Before you begin, familiarize yourself with the concepts of transactions in SQL Server.TransactionA transaction in SQL Server is a single unit of work. If a transaction succeeds,

) An explicit transaction is a transaction that has an explicit start-end tag, or the beginning is implicit, and the end of the transaction is explicitly marked. (BEGIN TRANSACTION transaction starts--COMMIT transaction ends--rollback transaction error rollback)(3) Automatic transactions are automatically default by the system, beginning and ending without marking. 2. Concurrency control 2.1 Common concurrency concurrency consistency issues include: Lost Modifications (lost update), read dirty d