ML Wiki

Isolation

A transaction is a sequence of updates to the database

• a transaction must be consistent
• 
• we need to ensure that all the transactions run in isolation
• that is, while one transactions is running, no other transaction should see its intermediate results (which can be inconsistent)

Causes

Data Sharing (Concurrency)

• suppose that two transactions $T_1$ and $T_2$ are running at the same time
• $T_1$: give 10% rise to all programmers
• $T_2$: transfer some programmers to business analysts

Problem here:

• it should be either first $T_1$ and then $T_2$ or vice-versa
• otherwise there will be a lot of problems and unexpected results
• Concurrency Control techniques are used for that

Transaction Manager

• Transaction Manager is a component of a DBMS that has a scheduler
• The scheduler is responsible for creating an impressions that all transactions are run in isolation

Levels of Isolation

• Serializable (see Serializable Scheduling)
• ...
• ...
• No Isolation (actions of transactions can be executed in any order)

See also

• ACID

Sources

• Database Systems Architecture (ULB)