Title: Write Caching with Reduced Durability
Tim Blackman
Sun Labs


Online games and virtual worlds can benefit from the consistency
guarantees provided by transactions, but their unique requirements
present a challenge when the size of the simulated worlds forces them to
be spread across multiple servers.  In particular, transactions in such
systems require very low latency and perform many writes, but do not
require full durability.  These special characteristics motivate
exploring a new approach to achieving scalability when implementing the
transaction system.

The approach requires that data and the computations that modify it be
clustered together on the same node.  Each node's commit updates are
streamed to a central storage point, but local transactions can proceed
without waiting for a network round trip for acknowledgement.  Only if
another node needs this node's data does the system need to wait for
confirmation that commit updates have been made persistent in a central
location.  So long as there is good locality of data and computation,
this approach promises to provide single-node performance while
permitting scaling to multiple nodes.  This approach takes advantage of
the high network bandwidth currently available to achieve low latency
without placing the requirement for low latency on to the network.  In
addition, individual nodes do not maintain data needed for long-term
storage, so they can be discarded if they fail, with only minor
consequences to users.