[CSC2231] Paper Review: Distributed Schedule Management in the Tiger Video Fileserver

Tiger is a video server built from a cluster of commodity hardware.
Tiger load-balances its machines (cubs) by having different cubs to
serve different parts of a video file (blocks). Tiger also uses a
technique called "coherent hallucination", which allow cubs to maintain
partial and possible inconsistent video delivery schedule. Coherent
hallucination is powerful because it limits the amount of states kept at
each cub while keeping the global schedule consistent.

I find this work kind of similar to P2P file sharing in terms of storage
requirement, but the video delivery has real-time requirements. To meet
real-time deadlines is a hard problem, as most of the effort discussed
in the paper is contributed to this problem. Tiger attempts to solve
this problem by having each cub well aware of the upcoming schedule of
delivery so that there is enough time to react to problems such as cub
failures.

Although the idea of coherent hallucination is important to this work, I
find it more than trivial. At a particular moment in time, each cub's
schedule may look different. This is because cub i has a block-play-time
amount of lead time ahead of cub i+1; in other words, the schedule of
cub i+1 is in sync with the schedule of cub i block-play-time before, as
if the schedule is time-travelling between cubs. If the blocks of
different videos are not stored in the same cub order, then this
technique probably will not work because there is no such
time-travelling effect to keep these partial schedules consistent.
Received on Thu Dec 01 2005 - 09:53:34 EST