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https://issues.apache.org/jira/browse/CALCITE-3963?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17127240#comment-17127240
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Xiening Dai commented on CALCITE-3963:
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Thanks for your reply, Julian.
I don't feel that current RelSet can be modeled as semigroups. What would be
the binary operation that satisfies associative property in RelSet?
My approach actually is pretty straightforward. I use the first RelNode in the
set by default to report RelSubset statistics, with two exceptions MultiJoin
and TableScan (for MV). Following the same approach, I update the other meta
handlers, and it works fine. We no longer need the hacks put in previously
(such as CALCITE-1018), and there's no more ambiguities around RelSubset stats
calculation. See latest patch - https://github.com/apache/calcite/pull/1992
I'd suggest we move forward with current approach. If there's a need in the
future for a fold operation across RelSubset, we could still update meta
handler to do so. But at this point, I don't see it is necessary.
> Maintain logical properties at RelSet (equivalent group) instead of RelNode
> ---------------------------------------------------------------------------
>
> Key: CALCITE-3963
> URL: https://issues.apache.org/jira/browse/CALCITE-3963
> Project: Calcite
> Issue Type: Bug
> Reporter: Xiening Dai
> Assignee: Xiening Dai
> Priority: Major
> Time Spent: 0.5h
> Remaining Estimate: 0h
>
> Currently the logical properties (such as row count, distinct row count, etc)
> are maintained at RelNode level. This creates a number of meta data
> consistency problems, e.g. CALCITE-1048, CALCITE-2166.
> In theory, all RelNodes in a RelSet should share the same logical properties
> per definition of relational equivalence. So it makes more sense to keep
> logical properties at RelSet level, rather than the RelNode. And such
> properties shouldn't change when new sub set is created or subset's best is
> changed.
> Specifically I think below build in metadata should fall into the logical
> properties category -
> Selectivity
> UniqueKeys
> ColumnUniqueness
> RowCount
> MaxRowCount
> MinRowCount
> DistinctRowCount
> Size (averageRowSize, averageColumnSize)
>
>
>
>
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