Partial read from peer-to-peer databases

In this paper we propose Scoop, a mechanism to implement the “partial read operation” for peer-to-peer databases. A peer-to-peer database is a database that its relations are horizontally fragmented and distributed among the nodes of a peer-to-peer network. The partial read operation is a data retrieval operation required for approximate query processing in peer-to-peer databases. A partial read operation answers to β-queries: given β ∈ [0, 1] and a relation R, a fraction β of the tuples in R must be retrieved from the database to answer a β-query. Despite the simplicity of the β-query, due to the distributed, evolving and autonomous nature of the peer-to-peer databases correct and efficient implementation of the partial read operation is challenging. Scoop is designed based on an epidemic dissemination algorithm. We model the epidemic dissemination as a percolation problem and by rigorous percolation analysis tune Scoop per-query and on-the-fly to answer β-queries correctly and efficiently. We prove the correctness of Scoop by theoretical analysis, and verify the efficiency of Scoop in terms of query cost and query time via extensive simulation.