Multi-dimensional Queries in P2P Systems

Applications

Photo-sharing (photographs tagged with metadata)

Multi-player online games (locate objects and other users)

System’s Components

Partitioning Strategy (distribute data across nodes)

Routing Strategy (transmit a query to the relevant nodes)

SCRAP: SPACE-FILLING CURVES WITH RANGE PARTITIONING

Partitioning Strategy

Data are mapped into a single dimension e.g. (0100,0101) -> 01000101

Single-dimensional data are range-partitioned across a dynamic set of nodes

Routing Strategy

Multi-dimensional range query is converted to a set of 1-d range queries

Route each of 1-d range queries (Skip graph: A Chord-like connection between the nodes, which promises O(logn) messages)

Desiderata

Locality: Nearby data points in the multi-dimensional space are also adjacent in the single dimension

Load Balance: Management of neighboring ranges Node with empty partition splits the

range of heavily loaded node

Desiderata Minimal metadata : Each node

knows only partition boundaries of itself and its neighbors

Low state : O(logn) links per node Routing load balance : Achieved due

to the symmetric nature of skip graphs

Query routing : O(logn) hops for each 1-d

Questions?