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application (16 bit) | table (16 bit) | address (64 bit) |
Approaches
Mapping
Tradeoff: Capacity, Throughput (via parallel requests) vs Latency (lookup time)
RAMCloud Address -> Physical storage location as quickly as possible (e.g. with as few requests and as little processing as possible).
Ideal: 0 network messages and O(1) address to host mapping time
Implies all clients are aware of mapping.
Complication: access-control requires highly-consistent mapping replication if control is on addresses (e.g. the application/table is part of the structured address).
DHT
- + Simple
- + Natural replication
- - Latency
- Address to shard mapping has log(# shards) time in general
- Can be mitgated for index space tradeoff using radix tree or tries
- How many levels is too deep? Even 2-3 in the face of cache misses?
- + Load sharing
- - More difficult to co-locate related data on a single machine
- Probably the case that we want to intentionally distrbute related data (more network overhead, but reduces latency because lookups happen on independent machines)
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