Review for Gemini (OSDI'12)

The problem that data consistency is hard to maintain in a large scale system. However, the synchronization of concurrent actions across the data center introduces large overhead.

Basically, there are two kinds of solutions. First one like Amazon's Dynamo, it sacrifices the data consistency level, but has low latency across the cluster. The second is like Yahoo's PNUTS, which can achieve strong data consistency but with high latency during data updates.

The problem that Gemini wants to tickle is to make a trade-off between the data consistency level and latency. Basically, Gemini allows multiple level of consistency to be co-existed. They propose so-called "RedBlue" strategy. More precisely, Blue operations execute locally and lazily, with low constancy level. Red operations are serialized and immediate require cross-site coordination.

The difference of Gemini from other related works are listed on the figure above.

Personally, I think Gemini will be influential within 10 years since it can reasonably balance the data consistency level and scalability.