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Displaying posts with tag: isolation levels (reset)
Understanding MySQL Isolation Levels: Repeatable-read

Isolation levels are a rare subject in MySQL literature. The documentation provides a terse description and focuses mainly on locking issues, but does not discuss the semantics of each isolation level. This is not only a problem that affects MySQL documentation but also the SQL standard itself.

Both the lack of documentation and the absence of a deeper description of the expected behavior in the SQL standard make isolation levels a topic that is more assumed than known by database administrators and developers. In this blog post, I aim to help you understand how the default isolation level in MySQL works and show you some surprising facts about it.

But first let’s see how isolation levels are described in the standard: “The transaction isolation level of a SQL-transaction defines the degree to which the operations on SQL-data, or schemas in that SQL-transaction are affected by the effects of and can affect operations on …

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A beginner’s guide to the Phantom Read anomaly, and how it differs between 2PL and MVCC

Introduction Unlike SQL Server which, by default, relies on the 2PL (Two-Phase Locking) to implement the SQL standard isolation levels, Oracle, PostgreSQL, and MySQL InnoDB engine use MVCC (Multi-Version Concurrency Control). However, providing a truly Serializable isolation level on top of MVCC is really difficult, and, in this post, I’ll demonstrate that it’s very difficult … Continue reading A beginner’s guide to the Phantom Read anomaly, and how it differs between 2PL and MVCC →

Understanding InnoDB transaction isolation levels

Isolation is an important part of ACID properties that guarantee that transactions are processed in a reliable manner. But there are four different levels of isolation available and you have to understand each one of them to be able to select the correct one for your needs. This post intends on explaining the four levels together with their effects on locking and performance.

Showing entries 1 to 3