[IGNITE-16430] Calcite engine. Sorted index spool with sorting can't be planned

• Type: Improvement
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Labels: calcite2-required calcite3-required
• Assignee: Unassigned
• Reporter: Aleksey Plekhanov
• Created: 30/Jan/22 08:58
• Updated: 31/Jan/22 13:10

Description

Currently, we have code in FilterSpoolMergeToSortedIndexSpoolRule that creates a sorted spool even if the input collation is empty. In this case, collation is created by index condition and the new sort node is inserted before the spool. But such a plan can never be chosen as the best plan since when we calculate the cumulative cost for the nested loop correlated join, we multiply left side rows count to right side commutative cost not taking into account rewind cost. Currently, cumulative cost for filter + spool = CPU: n + n, memory: 0 + n, for sorted spool + sort = CPU: log n + n*log n, memory: n + n. So, the cost for filter + spool will always be better than the cost for sorted spool + sort and sorted spool + sort never can be chosen. But for example, for sorted spool with sort rewind CPU cost is only log n since sorting is required only once and rewind CPU cost of filter + spool is n + n. So, starting from some iteration count cost of iterations * rewind cost + cumulative cost will be better than iterantions * cumulative cost, and sorted spool + sort will be chosen in this case.

Issue Links

• is part of: IGNITE-12248 Apache Calcite based query execution engine