Abstract. Ensuring the freshness of client data is a fundamental problem for
applications that rely on cloud infrastructure to store data and mediate sharing. Thialfi is a notification service developed at Google to simplify this task. Thialfi supports applications written in multiple programming languages and running on multiple platforms, e.g., browsers, phones, and desktops. Applications register their interest in a set of shared objects and receive notifications when those objects change. Thialfi servers run in multiple Google data centers for availability and replicate their state asynchronously. Thialfi’s approach to recovery emphasizes simplicity: all server state is soft, and clients drive recovery and assist in replication. A principal goal of our design is to provide a straightforward API and good semantics despite a variety of failures, including server crashes, communication failures, storage unavailability, and data center failures.
Some notes: Version updates come from the application server and as a result the application server should maintain the new version number for the objects it shares with the clients. This implies that Thialfi imposes a requirement for versioning objects whereas in many cases versioning may not be even needed.
They consider only 10% of the clients to be online most of the time and measurements are taken for cases where the number of clients is not really high, an increase in the number of clients would change the metrics (drastically?).
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