CDDTA-JOIN: One-Pass OLAP Algorithm for Column-Oriented Databases

Abstract

Row-store commonly uses a volcano-style “once-a-tuple” pipeline processor for processing efficiency but looses the I/O efficiency when only a small part of columns are accessed in a wide table. The academic column-store usually uses “once-a-column” style processing for I/O and cache efficiency but it has to suffer multi-pass column scan for complex query. This paper focuses on how to achieve the maximal gains from storage models for both pipeline processing efficiency and column processing efficiency. Based on the “address-value” mapping for surrogate key in dimension table, we can map incremental primary keys as offset addresses, so the foreign keys in fact table can be utilized as native join index for dimensional tuples. We use predicate vector as bitmap vector filters for dimensions to enable star-join as pipeline operator and pre-generate hash aggregators for aggregat based on the column. Using these approaches, star-join and pre-grouping can be completed in one-pass scan on dimensional attributes in fact table, and the following aggregate column scanning responses for the sparse accessing aggregation. We can gain both I/O efficiency for vector processing and CPU efficiency for pipeline aggregating. We perform the experiments for both simulated algorithm based on the column and the commercial column-store database.