Julian Hyde created OPTIQ-357:
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Summary: Run heuristic join algorithm several times with noise
Key: OPTIQ-357
URL: https://issues.apache.org/jira/browse/OPTIQ-357
Project: Optiq
Issue Type: Bug
Reporter: Julian Hyde
Assignee: Julian Hyde
The heuristic join algorithm (OptimizeBushyJoinRule) is a greedy algorithm and
is therefore (I surmise) prone to fall into local minima. If this behavior is
observed, a solution would be to run the algorithm several times with some
random noise added to the cost function. (Or randomly with small probability
taking the 2nd or 3rd best edge rather than the 1st best edge at each step.)
Compare the distinct generated plans according to a cost function, and pick the
best (or perhaps best N).
We should wait until we have some cases of the algorithm producing sub-optimal
plans before we proceed with this.
Note that the algorithm is also susceptive to bad cost estimates (especially in
join selectivity) and this won't help with those.
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