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Abstract: Many database applications perform complex data retrieval and update tasks.Nested queries, and queries that invoke user-defined functions, which arewritten using a mix of procedural and SQL constructs, are often used in suchapplications. A straight-forward evaluation of such queries involves repeatedexecution of parameterized sub-queries or blocks containing queries andprocedural code.An important problem that arises while optimizing nested queries as well asqueries with joins, aggregates and set operations is the problem of finding anoptimal sort order from a factorial number of possible sort orders. We showthat even a special case of this problem is NP-Hard, and present practicalheuristics that are effective and easy to incorporate in existing queryoptimizers.We also consider iterative execution of queries and updates inside complexprocedural blocks such as user-defined functions and stored procedures.Parameter batching is an important means of improving performance as it enablesset-orientated processing. The key challenge to parameter batching lies inrewriting a given procedure-function to process a batch of parameter values. Wepropose a solution, based on program analysis and rewrite rules, to automatethe generation of batched forms of procedures and replace iterative databasecalls within imperative loops with a single call to the batched form.We present experimental results for the proposed techniques, and the resultsshow significant gains in performance.

Autor: Ravindra Guravannavar

Fuente: https://arxiv.org/

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