Maryann Xue created CALCITE-830:
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Summary: VolcanoPlanner may have inconsistent state and may not
pick the cheapest plan if stats (e.g. row count) is not monotonic increasing
with cost
Key: CALCITE-830
URL: https://issues.apache.org/jira/browse/CALCITE-830
Project: Calcite
Issue Type: Bug
Reporter: Maryann Xue
Assignee: Julian Hyde
An example can be:
select i.item_id, o.quantity from orderTable o join (select distinct item_id
from itemTable) i on o.item_id = i.item_id
where item_id is the primary key of itemTable and thus is unique (distinct).
The AggregateRemoveRule will be applied for the subquery "select distinct
item_id from itemTable", and generates a cheaper sub-tree equivalent to "select
item_id from itemTable". However the original Rel sub-tree gives a smaller
rowCount (it shouldn't have, but let's say it's an independent issue) than the
new Rel sub-tree (after applying AggregateRemoveRule). By picking the new Rel
sub-tree as the new best of the child subset, the parent RelNode "Join" now has
a higher cost, but this change is not reflected in its own enclosing subset,
which then causes inconsistency.
Please see the attached log:
line 27099 ~ 27100:
{code}
rel#221:Subset#5.PHOENIX_CLIENT.[0], best=rel#220,
importance=0.4984472052723946
rel#220:PhoenixToClientConverter.PHOENIX_CLIENT.[0](input=rel#50:Subset#5.PHOENIX_SERVERJOIN.[0]),
rowcount=525.0, cumulative cost={153.3897966465855 rows, 6 2.0 cpu, 0.0
io}
{code}
line 27092 ~ 27093:
{code}
rel#50:Subset#5.PHOENIX_SERVERJOIN.[0], best=rel#49,
importance=0.4984472052723946
rel#49:PhoenixServerJoin.PHOENIX_SERVERJOIN.[[0]](left=rel#47:Subset#1.PHOENIX_SERVER.[0],right=rel#48:Subset#4.PHOENIX_CLIENT.[],condition==($1,
$3),joinTyp e=inner), rowcount=525.0, cumulative cost={193.63272822430963
rows, 62.0 cpu, 0.0 io}
{code}
rel#220 has a lower cumulative cost than its input rel#50.
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