Handle cardinality estimation for disjoint inner and outer joins #3848
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Dandandan
approved these changes
Oct 17, 2022
alamb
approved these changes
Oct 18, 2022
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Thanks @isidentical |
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Which issue does this PR close?
Closes #3802 .
Rationale for this change
When we know for a fact that an inner join is disjoint, we can estimate the cardinality of an inner join with (at least) one disjoint column as
0. From there, we can derive the cardinality of a left/right and full outer joins.What changes are included in this PR?
We now take an
is_exactflag inestimate_join_cardinalitywhich is onlytruewhen both left and right are originating directly from table providers (which might change in the future if we collect more statistics during materialization points both in DF and Ballista, and somehow adaptively optimize the parent plans according to that). If thatis_exactflag is true and if we identify a disjoint column when calculating the inner join cardinality, we now infer the cardinality of an inner join as 0.Since the cardinality of left/right/full outer joins can be derived from the inner join's cardinality (e.g. a disjoint left outer join would result with the number of rows from the left side), this PR also adds support for inferring their cardinality.
Are there any user-facing changes?
No.