features: skip result-set producers with an empty dependency#562
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cportele wants to merge 1 commit into
Open
features: skip result-set producers with an empty dependency#562cportele wants to merge 1 commit into
cportele wants to merge 1 commit into
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A multi-query that uses result sets materializes them level by level: each producer runs once, and its members are inlined into the consuming filters. A producer whose own filter references another result set that materialized to no members - in a boolean position that forces the filter false - can only ever return an empty set itself, yet it was still issued as a query. Evaluate the producer filter against the sets materialized so far with a three-valued (true/false/indeterminate) pass over AND/OR/NOT before running it: when the result is provably false, record the empty set and skip the query. The evaluation is conservative - any leaf not pinned to false by an empty set is indeterminate - so a producer is skipped only when boolean algebra guarantees an empty result, and the output is unchanged. This is a statement-count reduction that grows with the share of branches that are empty for a request. A skipped producer would otherwise resolve to a constant-false predicate (1 = 0) that the database discards without scanning a table, so no per-row or dataset-size cost is avoided.
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A multi-query that uses result sets materializes them level by level: each producer runs once, and its members are inlined into the consuming filters. A producer whose own filter references another result set that materialized to no members - in a boolean position that forces the filter false - can only ever return an empty set itself, yet it was still issued as a query.
Evaluate the producer filter against the sets materialized so far with a three-valued (true/false/indeterminate) pass over AND/OR/NOT before running it: when the result is provably false, record the empty set and skip the query. The evaluation is conservative - any leaf not pinned to false by an empty set is indeterminate - so a producer is skipped only when boolean algebra guarantees an empty result, and the output is unchanged.
This is a statement-count reduction that grows with the share of branches that are empty for a request. A skipped producer would otherwise resolve to a constant-false predicate (1 = 0) that the database discards without scanning a table, so no per-row or dataset-size cost is avoided.