Aleksey Plekhanov created IGNITE-16430:
------------------------------------------
Summary: Calcite engine. Sorted index spool with sorting can be
planned
Key: IGNITE-16430
URL: https://issues.apache.org/jira/browse/IGNITE-16430
Project: Ignite
Issue Type: Improvement
Reporter: Aleksey Plekhanov
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.
--
This message was sent by Atlassian Jira
(v8.20.1#820001)
