Join Synopses for Approximate Query Answering

In large data warehousing environments, it is often advantageous to provide fast, approximate answers to complex aggregate queries based on statistical summaries of the full data. In this paper, we demonstrate the difficulty of providing good approximate answers for join-queries using only statistics (in particular, samples) from the base relations. We propose join synopses as an effective solution for this problem and show how precomputing just one join synopsis for each relation suffices to significantly improve the quality of approximate answers for arbitrary queries with foreign key joins. We present optimal strategies for allocating the available space among the various join synopses when the query work load is known and identify heuristics for the common case when the work load is not known. We also present efficient algorithms for incrementally maintaining join synopses in the presence of updates to the base relations. Our extensive set of experiments on the TPCD benchmark ...

• Type: Conference
• Year: 1999
• Where: SIGMOD
• Authors: Swarup Acharya, Phillip B. Gibbons, Viswanath Poosala, Sridhar Ramaswamy
• Keywords: Approximate Answers, Base Relations, Database, Join Synopses, SIGMOD 1999