cwash into software

In Part 1, we covered the basic concept of a transaction, what the ACID properties are and how they specify transactional behavior, and why you might use transactions. This time, we’ll talk more specifically about what it’s like to use a transaction, and how the contracts it provides allow us to write data in a reliable fashion.

Programming With Transactional Systems

Commit and Rollback

Transactions either commit or rollback. Until a transaction is committed, it is assumed none of the work it has done is saved. Once a commit signal is issued by the application (either through an API call, or by a container), this work is actually performed by the transaction processing engine that’s being used. If for some reason the commit fails due to an error scenario, or some other runtime exception occurs, we assume that the integrity of the transaction has been compromised and the transaction rolls back, removing any work done up to that point. When a rollback occurs, the transaction must be resubmitted. (continue reading…)

Preface

This work came out of an lack of consistent, cohesive documentation for beginners on transactions. Similar material does exist, but much of it suffers from either being hard to find, scattered and spotty, or not written at a basic enough level where prerequisite knowledge is not required in order to understand the material covered. Over the course of this series of articles, we’ll talk about what concepts you need to know in order to effectively and correctly make use of transactions in your applications. This series of articles is written as a set of core concepts to understanding the basics of transactions, and is intended for junior to intermediate level developers, but my hope is that others will benefit from this series as well. As always, feedback is greatly appreciated.

What is a transaction?

Etymology

The word transaction comes from the Latin word transactionem meaning “an agreement, accomplishment,” which itself comes from the past participle of the verb transigere, transactus, meaning “drove or carried through.”

Transactions defined

The word’s definition is typically related to business or economics, meaning a single business deal, or an exchange of goods between two parties. Most introductions to transactions use an example of debiting one bank account and crediting another. When we remove funds from one account, we need to make sure that they are deposited into the other. If something fails (sufficient funds do not exist in the account being debited, or the account being credited has been closed) then both accounts need to be returned to their original state before the exchange began. This is actually a very good example, but how does that apply to software?

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