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Editor to share with you what the database isolation levels are, I believe most people do not know much about it, so share this article for your reference, I hope you can learn a lot after reading this article, let's learn about it!

Database isolation levels include: 1, read uncommitted; 2, read submitted; 3, repeatable read; 4, serialization. Low-level isolation levels generally support higher concurrent processing and have lower system overhead.

I. the concept of transaction

A series of operations in a transaction are either successful or none at all.

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There are two ways to end a transaction. When all the steps in the transaction are executed successfully, the transaction commits. If one of the steps fails, a rollback operation occurs, undoing the action that has been performed by the transaction.

Second, the characteristics of the transaction ACID

Transactions have four characteristics: Atomicity, Consistency, Isolation and Durability, referred to as ACID for short.

III. The problem of concurrent execution of multiple transactions

(1) dirty read: transaction 1 updated the record, but did not commit, transaction 2 read the updated row, and then transaction T1 rolled back, now T2 read is invalid.

(2) non-repeatable reading: when transaction 1 reads the record, transaction 2 updates the record and commits it. When transaction 1 reads it again, you can see the modified record of transaction 2.

(3) Phantom reading: when transaction 1 reads records, transaction 2 increases records and commits them. When transaction 1 reads records again, you can see the new records of transaction 2.

IV. Four isolation levels of transactions

The SQL standard defines four types of isolation levels, including specific rules that define which changes inside and outside the transaction are visible and which are not. Low-level isolation levels generally support higher concurrent processing and have lower system overhead.

The above is all the contents of the database isolation level, thank you for reading! I believe we all have a certain understanding, hope to share the content to help you, if you want to learn more knowledge, welcome to follow the industry information channel!

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