When App Engine launched over two years ago, we offered a Datastore that was designed for quick, strongly consistent reads. It was based on a Master/Slave replication topology, designed for fast writes while still allowing applications to see data immediately after it was written. For the past six months, as you are probably aware, we’ve been struggling with some reliability issues with the App Engine Datastore. Over the course of the past few months, we’ve made major strides in fixing these issues. However, our experience with these issues has made us rethink some of our design assumptions. As we promised you in some of our outage reports earlier this year, we wanted to give you a more fundamental solution to the problem.
Today I’m proud to announce the availability of a new Datastore configuration option, the High Replication Datastore. The High Replication Datastore provides the highest level of availability for your reads and writes, at the cost of increased latency for writes and changes in consistency guarantees in the API. The High Replication Datastore 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 application will remain fully available during planned maintenance periods, as well as during most unplanned infrastructure issues. A more detailed comparison between these two options is available in our documentation.
From now on, when creating a new application, you will be able to select the Datastore configuration for your application. While the current Datastore configuration default remains Master/Slave, this may change in the future.
The datastore configuration option can not be changed once an application is created, and all existing applications today are using the Master/Slave configuration. To help existing apps migrate their data to an app using the High Replication Datastore, we are providing some migration tools to assist you. First, we have introduced an option in the Admin Console that allows an application to serve in read-only mode so that the data may be reliably copied between apps. Secondly, we are providing a migration tool with the Python SDK that allows you to copy from one app to another. Directions on how to use this tool for Python and Java apps is documented here.
Now, a word on pricing: Because the amount of data replication significantly increases with the High Replication datastore, the price of this datastore configuration is different. But because we believe that this new configuration offers a significantly improved experience for some applications, we wanted to make it available to you as soon as possible, even though we haven’t finalized the pricing details. Thus, we are releasing the High Replication Datastore with introductory pricing of 3x that of the Master/Slave Datastore until the end of July 2011. After July, we expect that pricing of this feature will change. We’ll let you know more about the pricing details as soon as they are available, and remember, you are always protected when pricing changes occur by our Terms of Service. Due to the higher cost, we thus recommend the High Replication Datastore primarily for those developers building critical applications on App Engine who want the highest possible level of availability for their application.
Thank you, everyone, for all the work you’ve put into building applications on App Engine for the past two years. We’re excited to have High Replication Datastore as the first of many exciting launches in the new year, and hope you’re excited about the other things we’ve got in store for App Engine in 2011.
9 comments:
The important factor for my apps is speed. Otherwise my users are left staring at their phones waiting. Cannot work out what replication does in this respect....
Congrats datastore team.... a major milestone!
I hope an offshoot of this is that eventually datastore backups could be simplified. One click backup from the dashboard is needed.
The current state of backing up via brittle scripts that gradually dump entity data is a big weak point.
It sounds an awesome feature. Keep up the good work, thanks.
Thanks for this update. The is one think I would like to comment. Why do you limit developers to use only one datastore per app? It mite be much better to include additional parameter in datastore API to allow developers to access data in both datastores. As application developer it's hard to tell before hand what replication method better for any specific application. Personally I prefer more reliable solution for any project. But in some large applications there mite be some critical data and some less important data.
Speaking about current implementation. It's really weird that we do not have any way to migrate to High Replication Datastore without creating new application. It mite look not a big issue from Google's point of view, but that makes a lot of troubles to those developers, who use appspot domain to host applications. New application name means new domain name, etc.
Invitations for other developers don't work with highly-replicated apps because of "~" in their app_id.
Good thing for the high availability.
But what about the transactions occurred during down time after every thing is up.
Valuable feature, but would be nice to have this ability within a single app instead at the app-level granularity.
For example, a common use case: apps using a freemium business model would like to offer users the ability to pay and get upgraded to 'highly available' (high replication datastore). This requires both datastores in 1 app and the ability to selectively transition current data to high replication mode.
If it had this ability, appengine could offer a unique and revenue-generating feature: platform-supported "freemium business model" ability that would appeal to app developers, CFO-types, and end users!
Another use case: apps might want to store critical data in high replication (like billing data) and the rest of their data in the normal master/slave datastore.
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