Principles of relational database transaction adherence

Transactions are transaction in English, similar to real-world transactions, and have the following four features:

1, A (atomicity) atomicity
Atomicity is easy to understand, that is, all operations in a transaction are either done or not, and the transaction succeeds because all operations in the transaction are successful, and as long as one operation fails, the entire transaction fails and needs to be rolled back.

For example, bank transfer, transfer from a account 100 to B account, divided into two steps: 1) from a account 100 yuan, 2) deposited into the account of 100 to B. The two steps are either completed together, or not completed together, if only the first step, the second step fails, the money will be inexplicably less than 100 yuan.

2, C (consistency) consistency
Consistency is also relatively easy to understand, that is, the database should always be in a consistent state, the operation of the transaction will not change the original consistency of the database constraints.

For example, if an existing integrity constraint a+b=10, if a transaction changes A, then the B must be changed so that the transaction will still satisfy a+b=10, otherwise the transaction fails.

3, I (isolation) Independence
The so-called independence refers to the concurrent transactions do not affect each other, if one transaction to access the data is being modified by another transaction, as long as another transaction is not committed, the data it accesses is not affected by uncommitted transactions.
For example, there is a transaction from a to 100 yuan to the B account, in the case of the transaction is not completed, if at this time B query their own account, is not see the new increase of 100 yuan.

4, D (durability) Persistence
Persistence means that once a transaction commits, its modifications are persisted to the database, even if the outage occurs.

Principles of relational database transaction adherence