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https://issues.apache.org/jira/browse/DERBY-1260?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Dag H. Wanvik updated DERBY-1260:
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Derby Categories: [Performance]
> Investigate impact of infinite cost estimates on arithmetic
> operations/comparisons in the optimizer.
> ----------------------------------------------------------------------------------------------------
>
> Key: DERBY-1260
> URL: https://issues.apache.org/jira/browse/DERBY-1260
> Project: Derby
> Issue Type: Task
> Affects Versions: 10.2.1.6
> Reporter: A B
> Priority: Minor
>
> For large, deeply nested queries and/or queries with a high number of FROM
> tables/expressions with high row count estimates, the the resultant cost
> estimates can be multiplied--sometimes many times over--throughout the
> optimization process, which means that the overall query estimate can climb
> to a very large number very quickly. If the query is big enough, this can
> actually cause the optimizer to reach an estimated cost of INFINITY.
> That said, the current optimizer logic for costing and comparing access paths
> does not expect--and therefore does not account for--infinite cost estimates.
> As a result the optimizer does comparisons of, and basic arithmetic with,
> cost estimates and row counts that, when applied to estimtes of Infinity, can
> give unexpected results. One specific example of this is DERBY-1259.
> I'm filing this issue for the task of investigating the optimizer code more
> closely to see what other issues might exist when infinite cost estimates
> come into play.
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