Propagation characteristics and isolation level of spring transactions

Several propagation characteristics of transactions
1. propagation_required: If there is a transaction, the current transaction is supported. If no transaction is turned on
2. Propagation_supports: If there is a transaction, the current transaction is supported. If there is no transaction, the execution of the non-transaction
3. Propagation_mandatory: If a transaction already exists, the current transaction is supported. Throws an exception if there is no active transaction.
4. Propagation_requires_new: Always open a new transaction. If a transaction already exists, the existing transaction is suspended.
5. Propagation_not_supported: Always executes in a non-transactional manner and suspends any existing transactions.
6. Propagation_never: Always executes in a non-transactional manner and throws an exception if there is an active transaction
7. propagation_nested: If an active transaction exists, it is run in a nested transaction. If there is no active transaction,
Then press the Transactiondefinition.propagation_required property to execute

Isolation level for spring transactions
1. Isolation_default: This is a platfromtransactionmanager default isolation level, using the default transaction isolation level of the database.
The other four correspond to the isolation level of JDBC
2. Isolation_read_uncommitted: This is the lowest isolation level of a transaction, which allows a foreign transaction to see the uncommitted data for this transaction.
This isolation level produces dirty reads, non-repeatable reads, and Phantom reads.
3. isolation_read_committed: Ensure that a transaction modified data is committed before it can be read by another transaction. Another transaction cannot read uncommitted data for the transaction
4. Isolation_repeatable_read: This transaction isolation level prevents dirty reads and cannot be read repeatedly. However, Phantom reads may occur.
In addition to ensuring that one transaction cannot read uncommitted data from another transaction, it ensures that the following conditions are avoided (non-repeatable read).
5. Isolation_serializable This is the most cost-effective, but most reliable, transaction isolation level. Transactions are processed for sequential execution.
In addition to preventing dirty reading, non-repeatable reading, but also avoids phantom reading.

A description of some of these concepts:

Dirty read: Refers to when a transaction is accessing the data, and the data is modified, and this modification has not yet been committed to the database, then another transaction also accesses the data, and then used this data. Because this data is data that has not yet been submitted, the data that is read by another transaction is dirty, and the operation based on dirty data may not be correct.

Non-repeatable read: Refers to reading the same data multiple times within a transaction. When this transaction is not finished, another transaction accesses the same data. Then, between the two read data in the first transaction, the data that the first transaction two reads may be different because of the modification of the second transaction. This occurs when the data that is read two times within a transaction is not the same and is therefore called non-repeatable read.

Illusion reading: A phenomenon that occurs when a transaction is not executed independently, such as when the first transaction modifies data in a table, which involves all rows of data in the table. At the same time, the second transaction modifies the data in the table by inserting a new row of data into the table. Then the user who will be working on the first transaction in the future finds that there are no modified rows of data in the table, as if the illusion had occurred.

This article is from the Linux commune website (www.linuxidc.com) Source Link: http://www.linuxidc.com/Linux/2011-12/50178.htm

Propagation characteristics and isolation level of spring transactions