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application (16 bit) | table (16 bit) | address (64 bit) |
Approaches
Mapping
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)
- Extensible
- Linear
- Consistent
B-Trees
- + Supports range queries on totally ordered keys
- +/- Allows several records from the same table to be returned with a single request
- May cause a server to become a hot spot
- Extensible
- Linear
- Consistent
- RP*
Hashing
- Simple
- Likely to spread the load better
- If a single request needs multiple records from a table, it's likely to require separate requests to multiple servers, which adds overhead
- Is this anymore true than with hashing?
Replication
Effects
- + Throughput
- + Mitgates hot spots
- + Latency
- Eliminates cross data center requests
- - Consistency
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