Abstract: Methods, systems, and apparatus, including computer programs encoded on computer storage media, for dynamic partition selection. One of the methods includes receiving a representation of a query plan generated for a query, wherein the query plan includes a dynamic scan operator that represents a first computing node obtaining tuples of one or more partitions of a table from storage and transferring the tuples to a second computing node that executes a parent operator of the dynamic scan operator. A partition selector operator is generated corresponding to the dynamic scan operator. A location in the query plan is determined for the partition selector operator. A modified query plan is generated having the partition selector operator at the determined location.

Abstract: Methods, systems, and apparatus, including computer programs encoded on computer storage media, for dynamic partition selection. One of the methods includes receiving a representation of a query plan generated for a query, wherein the query plan includes a dynamic scan operator that represents a first computing node obtaining tuples of one or more partitions of a table from storage and transferring the tuples to a second computing node that executes a parent operator of the dynamic scan operator. A partition selector operator is generated corresponding to the dynamic scan operator. A location in the query plan is determined for the partition selector operator. A modified query plan is generated having the partition selector operator at the determined location.

Abstract: Methods, systems, and apparatus, including computer programs encoded on computer storage media, for dynamic partition selection. One of the methods includes receiving a representation of a query plan generated for a query, wherein the query plan includes a dynamic scan operator that represents a first computing node obtaining tuples of one or more partitions of a table from storage and transferring the tuples to a second computing node that executes a parent operator of the dynamic scan operator. A partition selector operator is generated corresponding to the dynamic scan operator. A location in the query plan is determined for the partition selector operator. A modified query plan is generated having the partition selector operator at the determined location.

Abstract: Query optimizer accuracy is tested by measuring the actual execution times on a database of each of a plurality of alternative query plans for each of a plurality of queries, first ranking the plans by the actual execution times, then ranking the plans by estimated execution times, and correlating the two rankings by computing a rank correlation metric. The rank correlation metric is normalized so that different optimizers can be objectively compared.

Abstract: Methods, systems, and apparatus, including computer programs encoded on computer storage media, for generating query plans for queries that include common table expressions. One of the methods includes receiving a query that includes a common table expression (CTE), wherein the CTE signifies that a system can compute a result for the query using a query plan that includes a CTE producer operator and a corresponding CTE consumer operator. A first query plan that includes a CTE producer operator and a corresponding CTE consumer operator and a second query plan that inlines an instance of the CTE consumer operator are generated. Respective costs are computed for the first query plan and the second query plan, and a result for the query is computed using the second query plan if the second query plan has a lower cost.

Abstract: Methods, systems, and apparatus, including computer programs encoded on computer storage media, for generating query plans for queries that include common expressions. One of the methods includes receiving an initial query plan generated for a query that includes multiple common expressions; identifying two or more matching subtrees of the initial query plan; generating an alternative query plan that includes a CTE producer operator and having an instance of one of the matching subtrees as one or more descendant operators of the CTE producer operator, including replacing at least one instance of a matching subtree in the initial query plan with a CTE consumer operator corresponding to the CTE producer operator; computing respective costs for the initial query plan and the alternative query plan; selecting the alternative query plan based on the cost for the alternative query plan; and computing a result for the query using the alternative query plan instead of the initial query plan.