Consistency Based Snapshot Management in Data Grids

Almost over the last 20 years grid technology has been developed to exploit unutilized computing capacity around the world. The two major application areas are solving computing intensive problems having less data (computational grid) or operating on large volumes of data (data grid). From a database perspective it is advisable to replicate data sets at different nodes in the grid before executing a single query. The query processor assigns a query to those nodes, which do not operate at full capacity and which have stored the appropriate replica. As the replica may be outdated usually a synchronization mechanism is necessary. This may be extremely expensive if full consistency between original data and replica is required. To avoid synchronization we follow the approach to store multiple versions of static snapshots. New versions of local data sets are distributed to the different nodes in the grid and added to the set of locally stored snapshots. Holding multiple versions of snapshots, the user has the possibility to combine snapshots taken at different points in time to get a more globally consistent , but possibly older view. The access to outdated snapshots is acceptable, if the user has knowledge about the degree of staleness or the degree of inconsistency if unsynchronized replicas are combined for a global view. This paper focuses on the quantification of the inconsistency and the snapshot management at inidividual members of a global data grid.