Things in the database

First, What is a thing

A program execution unit that accesses and possibly updates various data items in a database

Second, The role of things

To ensure consistency of data

Third, Four characteristics of things

Atomicity: A sequence of steps in a thing that is either executed or not executed

Consistency: Data in a database remains consistent before and after things are executed

Isolation: When multiple things access the same data at the same time, the effect of one thing on another

Persistence: When things are submitted or rolled back, the impact on the data is permanent, and any device failure or power outage will not affect the data retention

Four, The things in MySQL

1. Read Uncommit

It is possible to read data that is not submitted by another thing in one thing, which can produce dirty reads

2. Read commit(non-repeatable)

In one thing, it is impossible to read data that is not yet submitted by another thing, it is possible to read different data two times, so it becomes non-repeatable read

3. reapeatable Read(Repeatable read)

In one thing, even if another thing modifies the data and commits it, this thing still does not see the change of the data, unless this time the thing commits, opens a new thing

4. Serializable(serialized access)

When the database is in one thing, other things do not work on the database, must wait for things to commit or rollback, other things can be normal execution

Five, The things in the Orcale

1. Read Committed

In one thing, it is impossible to read data that has not yet been submitted by another thing, it is possible to read different data two times, so it becomes non-repeatable read ( same as MySQL)

2. Serializable

its role is only repeatable reading, equivalent to the third level in MySQL

Things in the database