What is Inter-Query Parallelism

Horizontal data partitioning is the process of splitting access objects into set of disjoint rows. It was first introduced in the end of 70’s and beginning of the 80’s (Ceri et al., 1982) for logically designing databases in order to improve the query performance by eliminating unnecessary accesses to non-relevant data. It knew a large success (in the beginning of the 80’s) in designing homogeneous distributed databases (Ceri et al., 1982; Ceri et al., 1984; Özsu et al., 1999) and parallel databases (DeWitt et al., 1992; Valduriez, 1993). In distributed environment, horizontal partitioning decomposes global tables into horizontal fragments, where each partition may be spread over multiple nodes. End users at the node can perform local queries/transactions on the partition transparently (the fragmentation of data across multiple sites/processors is not visible to the users.). This increases performance for sites that have regular transactions involving certain views of data, whilst maintaining availability and security. In parallel database context (Rao et al., 2002), horizontal partitioning has been used in order to speed up query performance in a sharednothing parallel database system (DeWitt et al., 1992). This will be done by both intra-query and intra-query parallelisms (Valduriez, 1993). It also facilitates the exploitation of the inputs/outputs bandwidth of the disks by reading and writing data in parallel. In this paper, we use fragmentation and partitioning words interchangeably.