Windows PowerShell Cookbook, 2nd Edition

Chapter 30. Transactions

Introduction

Transactions describe a system’s ability to support tentative or multistep changes. When you make changes within the context of a transaction, the system provides four main guarantees:

Isolation

To observers not participating in the transaction, the commands inside the transaction have not impacted the system.

Atomicity

Once you decide to finalize (commit) a transaction, either all of the changes take effect or none of them do.

Consistency

Errors caused during a transaction that would cause an inconsistent system state are dealt with in order to bring the system back to a consistent state.

Durability

Once the system has informed you of the transaction’s successful completion, you can be certain that the changes are permanent.

As a real-world example of a transaction, consider a money transfer between two bank accounts. This might happen in two stages: subtract the money from the first account, and then add the money to the second account. In this situation, you have the exact same goals for robustness and correctness:

Isolation

While the money transfer is taking place (but has not yet completed), the balance of both bank accounts appears unchanged.

Atomicity

At some point in the process, it’s possible that we’ve subtracted the money from the first account but haven’t added it yet to the second account. When we process the money transfer, it’s critical that the system never show this intermediate state. Either all of the changes take effect or none of them ...