You’ve probably heard the term database isolation level before, but how important is it? In other words, should you let your database admin worry about it, or should you care enough to be familiar with it? And if you should care, what are these different isolation levels anyway? The answer to that question depends on your situation, as well as your background in SQL and database administration. Here’s what you need to know about this important part of database management systems and why you need to care about it.
What are Database Transactions?
Database transactions are a set of instructions that are processed as a unit and which must be executed entirely or not executed at all. The database management system (DBMS) will either process the entire transaction or none of it. Transactions allow you to work with data in an organized and efficient manner.
What is a Database Isolation Level?
Database isolation levels are used to define the level of isolation from other transactions that a transaction can achieve when accessing data. The more isolated a transaction is, the less likely it will interfere with other transactions operating on the same data at the same time. There are four types of isolation levels: Read Uncommitted, Read Committed, Repeatable Read, Snapshot and Serializable.
Why it is important to pick the correct Isolation Level for your Database?
Choosing the right isolation level for your database is important for a number of reasons. When you choose the wrong setting, you can get strange side effects like phantom reads or dirty reads, which will throw off the results of queries and make it difficult to know what data is actually up-to-date. The best way to prevent these problems is to always check the documentation for your database before making any changes to your isolation level settings and truly understand what anomalies can occur.
What are the different isolation levels for a database?
The most common type of isolation is called read committed. This means that when you change the data, it will wait for the result to be committed before moving on.
Another type of isolation is called repeatable read. Repeatable read waits until the transaction has been completed and then proceeds to execute your query on this updated data set. If an error occurs during the transaction, any changes to the data are rolled back in order to maintain integrity.
The next type of isolation is serializable, which guarantees all queries have an identical outcome because they execute one at a time. It guarantees ordering among transactions with respect to locking rows exclusively; therefore serializable can’t be used in transactional systems because locks are held too long. Strongly consistent databases like CockroachDB only allows you to run in Serializable isolation as they believe the accuracy of data is the most important aspect of storing and retrieving data.
How do database isolation Levels work?
Database isolation levels work by allowing you to specify which transactions are permitted to see changes made by other transactions on the same data. This way, if a transaction is running at a lower isolation level, it can only see the changes of transactions that have run at the same level or higher.
The different levels that a database can be set to are: READ UNCOMMITTED, READ COMMITTED, REPEATABLE READ and SERIALIZABLE.
A more in-depth explanation of these can be found here