Google made available a new Datastore configuration option, “High Replication Datastore,” that provides the highest level of availability for reads and writes, at the cost of increased latency for writes and changes in consistency guarantees in the API.
“HRD increases the number of data centers that maintain replicas of your data by using the Paxos algorithm to synchronize that data across datacenters in real time. One of the most significant benefits is that all functionality of your app will remain fully available during planned maintenance periods, as well as during most unplanned infrastructure issues,” stated Google.
“From now on, when creating a new app, you’ll be able to select Datastore configuration. While the current default is Master/Slave, may change in future.
Dc option cann’t be changed once an app is created, all existing apps today are using Master/Slave. To help migrate to an app using HRD, we’re providing migration tools: First, an option in Admin Console allows an app to serve in read-only mode so that the data may be reliably copied between apps. Secondly, a migration tool with Python SDK that copies from one app to another,” explained Google.
HRD is currently avilable with introductory pricing of 3x that of Master/Slave Datastore until the end of July 2011.