FAS - A Freshness-Sensitive Coordination Middleware for a Cluster of OLAP Components
||FAS - A Freshness-Sensitive Coordination Middleware for a Cluster of OLAP Components
||U. Röhm, K. Böhm, H.-J. Schek, H. Schuldt
||Proceedings of the 28th International Conference on Very Large Data Bases (VLDB2002)Hong Kong, China
Data warehouses offer a compromise between freshness of data
and query evaluation times. However, a fixed preference ratio
between these two variables is too undifferentiated. With our
approach, clients submit a query together with an explicit
'freshness limit' as a new Quality-of-Service parameter.
Our architecture is a cluster of databases. The contribution
of this article is the design, implementation, and evaluation
of a coordination middleware. It schedules and routes updates
and queries to cluster nodes, aiming at a high throughput of
OLAP queries. The core of the middleware is a new protocol
called FAS (Freshness-Aware Scheduling) with the following
(1) The requested freshness limit of queries is always met, and
(2) data accessed within a transaction is consistent, independent
of its freshness.
Our evaluation shows that FAS has the following nice properties:
OLAP query-evaluation times are close (within 10%) to the ones
of an idealistic setup with no updates. FAS allows to effectively
trade 'up-to-dateness' for query performance. Even when all
queries request fresh data, FAS clearly outperforms synchronous
replication. Finally, mean response times are independent of
the cluster size (up to 128 nodes).
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