Caching multidimensional queries using chunks

ABSTRACT

Caching has been proposed (and implemented) by OLAP systems in order to reduce response times for multidimensional queries. Previous work on such caching has considered table level caching and query level caching. Table level caching is more suitable for static schemes. On the other hand, query level caching can be used in dynamic schemes, but is too coarse for “large” query results. Query level caching has the further drawback for small query results in that it is only effective when a new query is subsumed by a previously cached query. In this paper, we propose caching small regions of the multidimensional space called “chunks”. Chunk-based caching allows fine granularity caching, and allows queries to partially reuse the results of previous queries with which they overlap. To facilitate the computation of chunks required by a query but missing from the cache, we propose a new organization for relational tables, which we call a “chunked file.” Our experiments show that for workloads that exhibit query locality, chunked caching combined with the chunked file organization performs better than query level caching. An unexpected benefit of the chunked file organization is that, due to its multidimensional clustering properties, it can significantly improve the performance of queries that “miss” the cache entirely as compared to traditional file organizations.

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INDEX TERMS

Primary Classification:
  H. Information Systems
  H.2 DATABASE MANAGEMENT
      H.2.7 Database Administration
          Subjects: Data warehouse and repository

Additional Classification:
  G. Mathematics of Computing
  G.4 MATHEMATICAL SOFTWARE
      Subjects: Algorithm design and analysis

  H. Information Systems
  H.2 DATABASE MANAGEMENT
      H.2.1 Logical Design
          Subjects: Data models
      H.2.4 Systems
          Subjects: Query processing

General Terms:
Algorithms, Experimentation, Measurement