Tableau Software, Inc.

Manuel Then

Jan Finis

Tobias Muehlbauer

Thomas Neumann

Adrian Vogelsgesang

Richard Lee Cole

Alfons Kemper

Viktor Leis

Sebastian Hofstetter

Moritz Kaufmann

Michael Haubenschild

Richard Wesley

Pawel Terlecki

A method implements optimization of database queries by computing domain cardinality estimates. A client sends a database query to a server. The method parses the query to identify data columns. For each of the data columns, the method computes a lower bound and an upper bound of distinct data values using a pre-computed table size. The method also computes a patch factor by applying a pre-computed function to a ratio between a number of distinct data values that appear exactly once in a data sample and a number of distinct data values in the sample. Based on the patch factor, the lower bound, and the upper bound, the method computes an estimate of distinct values for each of the data columns. The method subsequently generates an execution plan for the query according to the computed estimates, executes the execution plan, and returns a result set to the client.

Computing domain cardinality estimates for optimizing database query execution

A database engine includes one or more computing devices, each having one or more processors and memory. The memory stores programs configured for execution by the processors. The database engine receives a database query from a client, and parses the database query to build a query operator tree. The query operator tree includes a plurality of query operators. The database engine performs one or more optimization passes on the query operator tree, including a deduplication optimization pass, to form an optimized execution plan. The deduplication optimization pass includes determining that a first query operator is equivalent to a second query operator during a traversal of the query operator tree, and replacing the second query operator with a link to reuse results from the first query operator. The database engine executes the optimized execution plan to retrieve a result set from the database and returns the result set to the client.

Elimination of query fragment duplication in complex database queries

A database engine receives a database query that specifies retrieving data from a data source. The database engine parses the query to build an operator tree that includes a TableScan operator configured to scan a table from the data source to produce outputs corresponding to a single data field from the table, and includes a GroupBy operator that groups rows of the table according to the data field. The database engine generates and executes code corresponding to the operator tree to retrieve a result set. When the TableScan operator is a child of the GroupBy operator and the outputs are independent of duplicate input rows from the table, execution of the TableScan operator comprises, for each storage block of rows from the table: determining a storage compression scheme for encoding the data field and, for certain encodings, using the encoding to produce the outputs without duplication of rows.

Optimizing domain queries for relational databases

A database engine receives a human-readable database query that includes a plurality of conditional expressions. The database engine parses the database query to build an operator tree that includes a subtree corresponding to each of the conditional expressions. The database engine identifies a subexpression that appears in two or more of the conditional expressions. The subexpression is executed conditionally. The database engine hoists the subexpression outside of the conditional expression so that it is executed unconditionally. The database engine modifies the operator tree to specify computation of a value for the subexpression a first time and to reuse the computed value when the subexpression is subsequently encountered. The database engine executes the modified operator tree to form a result set corresponding to the database query, thereby evaluating the subexpression only a single time for each row of input data and returns the result set.

Elimination of common subexpressions in complex database queries

A database engine receives a database query from a client. The database engine parses the database query to build a query operator tree that includes a plurality of query operators. The database engine performs one or more optimization passes on the query operator tree, including a deduplication optimization pass, to form an optimized execution plan. The deduplication optimization pass includes: creating a list of query operators via a first traversal of the query operator tree, determining a first query operator that is equivalent to a second query operator, based on a hash map, via a second traversal of the query operator tree, and substituting, via a third traversal of the query operator tree, the second query operator with a tree node that links to the first query operator. The database engine executes the optimized execution plan to retrieve a result set from the database, and returns the result set.

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Munich, Germany

Manuel Then