Abstract: A database system is operable to generate query output based on executing a plurality of operators of a query operator execution flow for a query. Executing each operator can include generating a set of output query rows based on processing a set of input query rows, maintaining execution tracking data for the each operator that includes at least one counter tracking at least one event type, and generating a set of execution tracking rows based on sampling the execution tracking data. The query output includes a final set of rows corresponding to a query resultant and a final set of execution tracking rows generated by at least one final operator based on an aggregation of a plurality of sets of execution tracking rows generated by the plurality of operators.

Abstract: A database system is operable to determine a query that includes a join expression for execution. A set of input rows are dispersed for processing via a plurality of parallelized join processes in conjunction with executing the join expression based on identifying a first proper subset of the set of input rows based on a null-handling strategy. First rows in the first proper subset are dispersed for processing across the plurality of parallelized join processes in accordance with the null-handling strategy. second rows in a set difference between the set of input rows and the first proper subset are dispersed across the plurality of parallelized join processes in accordance with a join key-based assignment strategy. The set of input rows are processed via the plurality of parallelized join processes.

Abstract: A database system is operable to determine a query for execution. The database system can execute a left join operation for the query based on receiving a plurality of left input rows, and forwarding all of the plurality of left input rows are forwarded. It is determined whether any right input rows match with each given left input row based on a hash map. When one right input row is identified as matching with the given left input row, a value of right input row is copied and emitted in conjunction with the given left input row. When no right input rows are identified as matching with the given left input row, a null value is emitted in conjunction with the given left input row.