Bypassing Joins in Disjunctive Queries

نویسندگان

  • Michael Steinbrunn
  • Klaus Peithner
  • Guido Moerkotte
  • Alfons Kemper
چکیده

The bypass technique, which was formerly restricted to selections only KMPS94], is extended to join operations. Analogous to the selection case, the join operator may generate two output streams|the join result and its complement|whose subsequent operator sequence is optimized individually. By extending the bypass technique to joins, several problems have to be solved. (1) An algorithm for exhaustive generation of the search space for bypass plans has to be developed. (2) The search space for bypass plans is quite large. Hence, partial exploration strategies still resulting in suuciently eecient plans have to be developed. (3) Since the complement of a join can be very large, those cases where the complement can be restricted to the complement of the semijoin have to be detected. We attack all three problems. Especially, we present an algorithm generating the optimal bypass plan and one algorithm producing near optimal plans exploring the search space only partially. As soon as disjunctions occur, bypassing results in savings. Since the join operator is often more expensive than the selection, the savings for bypassing joins are even higher than those for selections only. We give a quantitative assessment of these savings on the basis of some example queries. Further, we evaluate the performance of the two bypass plan generating algorithms .

برای دانلود متن کامل این مقاله و بیش از 32 میلیون مقاله دیگر ابتدا ثبت نام کنید

ثبت نام

اگر عضو سایت هستید لطفا وارد حساب کاربری خود شوید

منابع مشابه

Designing Views to Optimize Real Queries

This paper considers the following problem: given a query workload, a database, and a set of constraints, design a set of views that give equivalent rewritings of the workload queries and globally minimize the evaluation costs of the workload on the database under the constraints. We refer to this problem as “view design for query performance,” or “view design” for short; sets of views that sat...

متن کامل

An optimization of disjunctive queries: union-pushdown

Most previous works on query optimization techniques deal with conjunctive queries only because the queries with disjunctive predicates are complex to optimize. Hence, for disjunctive queries, query optimizers based on these techniques generate plans using rather simple methods such as CNFand DNF-based optimization. However, the plans generated by these methods perform extremely poorly for cert...

متن کامل

Processing Inequality Queries

Bernstein and Goodman showed that natural inequality ( NI) queries can be processed efficiently by semijoins, if there are no multiple inequality join edges, nor cycles with one or zero doublet. In this paper procedures to hand1 e these cases efficiently are given. Multiple inequality join edges can be processed by multi-attribute inequality semijoins. Two procedures based on generalized semi-j...

متن کامل

A Tractable Class of Disjunctive Deductive Databases

In general, computing answers to queries in disjunctive deductive databases is CoNP-complete and therefore computationally infeasible. However, there are some tractable classes of disjunctive databases. In this paper, we present polynomial time algorithms to compute answers to queries in one such tractable class of disjunctive databases where at most two atoms are allowed in any disjunction.

متن کامل

Negative Hyper-resolution as Procedural Semantics of Disjunctive Logic Programs

We prove that negative hyper-resolution is a sound and complete procedure for answering queries in disjunctive logic programs. In our formulation, answers of queries are defined using disjunctive substitutions, which are more flexible than answer literals used in theorem

متن کامل

ذخیره در منابع من


  با ذخیره ی این منبع در منابع من، دسترسی به آن را برای استفاده های بعدی آسان تر کنید

برای دانلود متن کامل این مقاله و بیش از 32 میلیون مقاله دیگر ابتدا ثبت نام کنید

ثبت نام

اگر عضو سایت هستید لطفا وارد حساب کاربری خود شوید

عنوان ژورنال:

دوره   شماره 

صفحات  -

تاریخ انتشار 1995