How Does MySQL Handle Read Consistency

Q

How Does MySQL Handle Read Consistency? - MySQL FAQs - Transaction Management: Commit or Rollback

✍: FYIcenter.com

A

Read consistency is a concept that describes how consistent the output will be on two subsequent read operations. A read operation is usually a stand alone SELECT statement or a SELECT subquery in a parent statement.

A database server can support up to 3 levels of read consistency:

No Read Consistency - Two subsequent read operations will get no consistent output, if other sessions are making changes to the database.
Statement-Level Read Consistency - Two subsequent read operations will get consistent output, if they are used as subqueries within a single SQL statement.
Transaction-Level Read Consistency - Two subsequent read operations will get consistent output, if they are used as subqueries or SELECT statements within a single transaction.

By default, MySQL server offers the highest level, Transaction-Level Read Consistency, on tables with transaction-safe storage engines, like InnoDB.

2007-05-11, 5289👍, 0💬

What Happens to the Current Transaction If a DDL Statement Is Executed
What Happens to the Current Transaction If a DDL Statement Is Executed? - MySQL FAQs - Transaction Management: Commit or Rollback If a DDL statement is executed, the current transaction will be committed and ended. All the database changes made in the current transaction will become permanent. This ... 2007-05-11, 5531👍, 0💬

How Does MySQL Handle Read Consistency
How Does MySQL Handle Read Consistency? - MySQL FAQs - Transaction Management: Commit or Rollback Read consistency is a concept that describes how consistent the output will be on two subsequent read operations. A read operation is usually a stand alone SELECT statement or a SELECT subquery in a par... 2007-05-11, 5290👍, 0💬

How To Rollback the Current Transaction
How To Rollback the Current Transaction? - MySQL FAQs - Transaction Management: Commit or Rollback If you have used some DML statements updated some data objects, you find a problem with those updates, and you don't want those updates to be permanently recorded in the database, you can use the ROLLB... 2007-05-11, 5092👍, 0💬

What Happens to the Current Transaction If a START TRANSACTION Is Executed
What Happens to the Current Transaction If a START TRANSACTION Is Executed? - MySQL FAQs - Transaction Management: Commit or Rollback If you are in a middle of a current transaction, and a START TRANSACTION command is executed, the current transaction will be committed and ended. All the database ch... 2007-05-11, 5045👍, 0💬

How To View and Change the Current Transaction Isolation Level
How To View and Change the Current Transaction Isolation Level? - MySQL FAQs - Transaction Management: Commit or Rollback If you want to view or change the current transaction isolation level, you can use the following commands: SELECT @@TX_ISOLATION FROM DUAL; -- Viewing the current transaction iso... 2007-05-11, 4985👍, 0💬

How To Experiment Data Locks
How To Experiment Data Locks? - MySQL FAQs - Transaction Management: Commit or Rollback If you want to have some experience with data locks, you can create two windows running two mysql transactions in two sessions. In session 1, you can run a UPDATE statement with REPEATABLE READ transaction isolat... 2007-05-11, 4982👍, 0💬

What Happens to the Current Transaction If the Session Is Killed
What Happens to the Current Transaction If the Session Is Killed? - MySQL FAQs - Transaction Management: Commit or Rollback If a session is killed by the DBA, the current transaction in that session will be rolled back and ended. All the database changes made in the current transaction will be remov... 2007-05-11, 4928👍, 0💬

What Are Transaction Isolation Levels
What Are Transaction Isolation Levels? - MySQL FAQs - Transaction Management: Commit or Rollback There are 4 transaction isolation levels defined by SQL-1992 standard: READ UNCOMMITTED - The SELECT statements in one transaction will read uncommitted data changes from transactions of all connected se... 2007-05-09, 4873👍, 0💬

What Is a Data Lock
What Is a Data Lock? - MySQL FAQs - Transaction Management: Commit or Rollback MySQL uses two types of data locks at two levels to provide you the transaction isolation level you need: Share Lock at Row Level (S) - A data row is locked by a transaction for reading. Exclusive Lock at Row Level (X) - ... 2007-05-09, 4777👍, 0💬

All rights in the contents of this web site are reserved by the individual author. fyicenter.com does not guarantee the truthfulness, accuracy, or reliability of any contents.