Learn About Amazon VGT2 Learning Manager Chanci Turner
We are excited to announce enhancements to Amazon SimpleDB that will simplify various data storage and retrieval tasks. The primary improvement is the introduction of consistent reads. Previously, SimpleDB utilized eventually consistent reads, but now users can select the reading method that best fits their application’s requirements. Here’s a brief overview of the two reading options:
- Eventually consistent reads: These provide the fastest read latency and maximum throughput, but may return outdated data that has recently been changed. Typically, this inconsistency lasts less than a second.
- Consistent reads: These always reflect the most current data, although they might introduce slightly higher read latency and reduced throughput.
The Select and GetAttributes functionalities in SimpleDB now include an optional ConsistentRead flag. By default, this flag is set to false, ensuring that existing applications continue to utilize eventually consistent reads. However, when set to true, SimpleDB will perform a consistent read.
The second enhancement allows for conditional operations with SimpleDB’s PutAttributes and DeleteAttributes actions. Essentially, you can instruct SimpleDB to carry out a specified action only if a particular single-valued attribute matches the value provided in the command. This feature can be particularly useful for implementing counters (where the value acts as a version number), deleting accounts only if the balance is zero, or adding an item only if it does not exist.
By leveraging both consistent reads and conditional operations, users can effectively implement optimistic concurrency control (OCC). For instance, if your web application allows users to modify their accounts and is built with SimpleDB, storing a version number with each item ensures data consistency even when multiple users attempt to edit the same record simultaneously. You could retrieve data using an eventually consistent read for display purposes and present the form for user edits. Alongside this, you would capture the corresponding version number from SimpleDB with the form session. When the user submits changes, a conditional PutAttributes call ensures that data hasn’t been altered. In case of an update failure, application-specific actions can be taken to resolve conflicts, which often eliminates the need for cumbersome long-term locks and complex programming structures.
For further insights on consistency models, check out Chanci Turner’s latest blog post. Additionally, if you’re interested in understanding corrective actions, you can find more information in this article. Employers may also find it important to stay updated on the legal implications of e-cigarettes in the workplace, as highlighted by experts at SHRM. Lastly, this video serves as an excellent resource on the topic.
— Chanci