Holos - OLAP Storage

OLAP Storage

Holos Server provided an array of different, but compatible, storage mechanisms for its multi-cube architecture: memory, disk, SQL. It was therefore the first product to provide "hybrid OLAP" (HOLAP). It provided a very versatile mechanism for joining cubes, irrespective of their storage technology, dimensionality, or meta-data, and this was eventually given a US patent (called COA—Compound OLAP Architecture U.S. Patent 6,289,352U.S. Patent 6,490,593). One novel aspect of this was a 'stack' feature that allowed read/write cubes to be stacked over read-only cubes. Read operations to the overall virtual cube then visited both 'racks' (top first, and then the bottom), whereas write operations only affected the top. The resulting valve-like mechanism found many applications in data sharing, what-if forecasting, and aggregation of slow SQL-based data. Since the overhead of the joining was small, it was not uncommon to have stacks 7 levels deep, and joining terabytes of real OLAP data. Around about V8.5, Holos Server implemented a hierarchical lock manager, allowing nesting of fine and coarse-grain OLAP locks, and full transaction control.