Monday, April 20, 2009

Scalling Out

Having multiple datacenters is becoming more important, both for better quality and fault tolerance. This article illustrate needs & problems of expanding a web service over multiple datacenters.

To solve cache consistency problem, they hacked MySQL to know when and what data is replicated - cache item is updated (actually deleted) when it is replicated.

Another problem they had was routing problem. As they allowed writing only on California databases, the user written to the database should remain on California until the entry is replicated to other datacenters to avoid confusion - and they picked 20 seconds for it.

Facebook's solutions looks practical enough, but far from general or formal solution. What if 3rd datacenter is coming? etc. Their solution only works for their settings and applications.

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