官术网_书友最值得收藏!

ACID properties

In a relational database, a single logical operation is called a transaction. The technical translation of a transaction is a set of database operations, which are createread, update, and delete (CRUD). An example of explaining a transaction is a budget assignment to several projects in the company assuming we have a fixed amount of money. If we increase a certain project budget, we need to deduct this amount of increase from another project. The ACID properties in this context could be described as follows:

  • Atomicity: All or nothing, which means that if a part of a transaction fails, then the transaction fails as a whole.
  • Consistency: Any transaction gets the database from one valid state to another valid state. Database consistency is governed normally by data constraints and the relation between data and any combination thereof. For example, imagine if someone would like to completely purge his account on a shopping service. In order to purge his account, his account details, such as a list of addresses, will also need to be purged. This is governed by foreign key constraints, which will be explained in detail in the coming chapter.
  • Isolation: Concurrent execution of transactions results in a system state that would be obtained if the transactions were executed serially.
  • Durability: The transactions that are committed—that is, executed successfully—are persistent even with power loss or some server crashes. In PostgreSQL, this is done normally by a technique called Write-Ahead Logging (WAL). Another database refers to this as a transaction log such as in Oracle.
主站蜘蛛池模板: 梅州市| 宝兴县| 孟连| 揭阳市| 台中市| 饶阳县| 栾城县| 堆龙德庆县| 锡林郭勒盟| 瑞金市| 深州市| 宁强县| 临颍县| 丰县| 陇西县| 筠连县| 绥中县| 定边县| 兴和县| 开平市| 文山县| 新蔡县| 陕西省| 吉安市| 崇州市| 玛纳斯县| 长春市| 陵川县| 大宁县| 临汾市| 西青区| 辽宁省| 台安县| 密山市| 高阳县| 手游| 新晃| 怀化市| 昌宁县| 南丹县| 孝感市|