What is a database transaction?

Question

Can someone provide a straightforward (but not simpler than possible) explanation of a transaction as applied to computing (even if copied from Wikipedia)?

Answer 1

A transaction is a sequence of one or more SQL operations that are treated as a unit.

Specifically, each transaction appears to run in isolation, and furthermore, if the system fails, each transaction is either executed in its entirety or not all.

The concept of transactions is motivated by two completely independent concerns. One has to do with concurrent access to the database by multiple clients, and the other has to do with having a system that is resilient to system failures.

Transaction supports what is known as the ACID properties:

• A: Atomicity;
• C: Consistency;
• I: Isolation;
• D: Durability.

Answer 2

I would suggest that a definition of 'transaction processing' would be more useful, as it covers transactions as a concept in computer science.

From wikipedia:

In computer science, transaction processing is information processing that is divided into individual, indivisible operations, called transactions. Each transaction must succeed or fail as a complete unit; it cannot remain in an intermediate state.

http://en.wikipedia.org/wiki/Transaction_processing#Implementations

Answer 3

http://en.wikipedia.org/wiki/Database_transaction
http://en.wikipedia.org/wiki/ACID
ACID = Atomicity, Consistency, Isolation, Durability

When you wish for multiple transactional resources to be involved in a single transaction, you will need to use something like a two-phase commit solution. XA is quite widely supported.

Answer 4

In addition to the above responses, it should be noted that there is, at least in theory, no restriction whatsoever as to what kind of resources are involved in a transaction.

Most of the time, it is just a database, or multiple distinct databases, but it is also conceivable that a printer takes part in a transaction, and can cause that transaction to fail, say in the event of a paper jam.

Answer 5

Transaction is an indivisible unit of data processing -All transactions must have the ACID properties:

ie:Atomicity,Consistency,Isolation and Durable Transaction is all or nothing but not intermidiate (it means if you transfer your money from one account to another account,one account have to lose that much and other one have to gain that amount,but if you transfer money from one account and another account is still empty that will be not a transaction)