xiong duan created CALCITE-7053:
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Summary: In HepPlanner, move down the collectGarbage to
topological order for better optimizer performance
Key: CALCITE-7053
URL: https://issues.apache.org/jira/browse/CALCITE-7053
Project: Calcite
Issue Type: Bug
Reporter: xiong duan
According to the java comment in HepPlanner#getGraphIterator:
{code:java}
// Make sure there's no garbage, because topological sort
// doesn't start from a specific root, and rules can't
// deal with firing on garbage.
// FIXME jvs 25-Sept-2006: I had to move this earlier because
// of FRG-215, which is still under investigation. Once we
// figure that one out, move down to location below for
// better optimizer performance.
{code}
Based on the current implementation, I haven't found the reason why the
depth-first order requires garbage collection every time. Since it always
starts the search from a specific
Vertex, the issue mentioned the FRG-215 -
I haven't found any description or information about this problem. Therefore,
this PR attempts to delegate the collectGarbage operation to the topological
order.
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