Understanding gmail
Wednesday, February 24, 2010
10:03 AM
Understanding gmail
Your mail messages are stored "in the cloud". 
Each message has a unique ID that serves as its key. 
There is no concept of message locality; two "adjacent" messages in your mailbox may be stored across the world from one another. 
The convenient human concept of locality (i.e., that messages are a stream) is constructed by MapReduce. 