Julian Hyde created CALCITE-794:
-----------------------------------
Summary: 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
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().
--
This message was sent by Atlassian JIRA
(v6.3.4#6332)
