On the optimal nesting order for computing N-relational joins
ACM Transactions on Database Systems (TODS)
Predicate migration: optimizing queries with expensive predicates
SIGMOD '93 Proceedings of the 1993 ACM SIGMOD international conference on Management of data
Experiences building the open OODB query optimizer
SIGMOD '93 Proceedings of the 1993 ACM SIGMOD international conference on Management of data
SIGMOD '94 Proceedings of the 1994 ACM SIGMOD international conference on Management of data
Optimizing disjunctive queries with expensive predicates
SIGMOD '94 Proceedings of the 1994 ACM SIGMOD international conference on Management of data
Query execution techniques for caching expensive methods
SIGMOD '96 Proceedings of the 1996 ACM SIGMOD international conference on Management of data
Optimization of queries with user-defined predicates
ACM Transactions on Database Systems (TODS)
Optimization and Evaluation of Disjunctive Queries
IEEE Transactions on Knowledge and Data Engineering
Optimization of Nonrecursive Queries
VLDB '86 Proceedings of the 12th International Conference on Very Large Data Bases
Advanced Query Processing in Object Bases Using Access Support Relations
VLDB '90 Proceedings of the 16th International Conference on Very Large Data Bases
Optimizing Boolean Expressions in Object-Bases
VLDB '92 Proceedings of the 18th International Conference on Very Large Data Bases
Bypassing Joins in Disjunctive Queries
VLDB '95 Proceedings of the 21th International Conference on Very Large Data Bases
Optimization of Queries with User-defined Predicates
VLDB '96 Proceedings of the 22th International Conference on Very Large Data Bases
Optimization of Queries Including ADT Functions
Proceedings of the Second International Symposium on Database Systems for Advanced Applications
Factorizing complex predicates in queries to exploit indexes
Proceedings of the 2003 ACM SIGMOD international conference on Management of data
On the optimal ordering of maps, selections, and joins under factorization
BNCOD'06 Proceedings of the 23rd British National Conference on Databases, conference on Flexible and Efficient Information Handling
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The query optimizer of a database system is confronted with two aspects when handling user-defined functions (UDFs) in query predicates: the vast differences in evaluation costs between UDFs (and other functions) and multiple calls of the same (expensive) UDF. The former is dealt with by ordering the evaluation of the predicates optimally, the latter by identifying common subexpressions and thereby avoiding costly recomputation. Current approaches order n predicates optimally (neglecting factorization) in O(n log n). Their result may deviate significantly from the optimal solution under factorization. We formalize the problem of finding optimal orderings under factorization and prove that it is NP-hard. Furthermore, we show how to improve on the run time of the brute-force algorithm (which computes all possible orderings) by presenting different enhanced algorithms. Although in the worst case these algorithms obviously still behave exponentially, our experiments demonstrate that for real-life examples their performance is much better.