Amazon SimpleDB Consistency Enhancements

Amazon SimpleDB Consistency Enhancements.

Abstract
This document outlines the new strong consistency features in SimpleDB - consistent read and conditional put/delete. It also demonstrates how they can be used to program key database application scenarios such as persistent application state, concurrency control, item counter, and conditional update/delete.

Contents
Consistent read
Consistent read vs. eventually consistent read
- Scenario 1: no R/W or W/W overlap
- Scenario 2: R/W overlap
- Scenario 3: W/W overlap
Conditional put and delete
- Conditional put
- Conditional delete
- API changes
Sample usage scenarios
- Persistant application state
- Optimistic concurrency control
- Counters
- Delete item if an attribute matches a certain value
- Insert an item only if it does not exist
Conclusion
Appendix: List of static and dynamic errors for conditional put and delete
- Static Errors
- Dynamic Errors