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https://issues.apache.org/jira/browse/DRILL-7457?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Paul Rogers updated DRILL-7457:
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Summary: Join assignment is random when table costs are identical (was:
Join assignment is random when table costa are identical)
> Join assignment is random when table costs are identical
> --------------------------------------------------------
>
> Key: DRILL-7457
> URL: https://issues.apache.org/jira/browse/DRILL-7457
> Project: Apache Drill
> Issue Type: Bug
> Reporter: Paul Rogers
> Priority: Minor
>
> Create a simple test: a join between two identical scans, call them t1 and
> t2. Ensure that the scans report the same cost. Capture the logical plan.
> Repeat the exercise several times. You will see that Drill randomly assigns
> t1 to the left side or right side.
> Operationally this might not make a difference. But, in tests, it means that
> trying to compare an "actual" and "golden" plan is impossible as the plans
> are unstable.
> Also, if only the estimates are the same, but the table size differs, then
> runtime performance will randomly be better on some query runs than others.
> Better is to fall back to SQL statement table order if the two tables are
> otherwise identical in cost.
> This may be a Calcite issue rather than a Drill issue.
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