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https://issues.apache.org/jira/browse/CALCITE-794?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Julian Hyde updated CALCITE-794:
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Fix Version/s: next
> Detect cycles when computing statistics
> ---------------------------------------
>
> Key: CALCITE-794
> URL: https://issues.apache.org/jira/browse/CALCITE-794
> Project: Calcite
> Issue Type: Bug
> Reporter: Julian Hyde
> Assignee: Julian Hyde
> Fix For: next
>
>
> The graph of RelNodes is allowed to be cyclic. This causes problems when
> evaluating certain metadata, for example RelMetataQuery.areColumnsUnique.
> While computing the value for RelNode r, it might recurse through say a
> Project and hit r again. This causes a stack overflow.
> We solve this by adding a map or set of active RelNodes. The map is stored
> within RelMetadataQuery, which can now be instantiated, and its methods are
> no longer static. The first call should instantiate a RelMetadataQuery, but
> all subsequent calls for metadata (perhaps several kinds of metadata) will
> use the same RelMetadataQuery instance, hence the same map.
> Also add a RelMetadataQuery argument to the static "handler" methods in
> RelMdColumnUniqueness and similar classes.
> This is a breaking change for people who have written a metadata handler, and
> might be subtle to detect, because the methods are invoked via reflection.
> For code that is just using RelMetadataQuery methods, the change is still
> breaking, but the break points and remedy will be obvious: the methods are no
> longer static, so they need to change RelMetadataQuery.foo() to
> RelMetadataQuery.instance().foo().
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