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From "Dag H. Wanvik (JIRA)" <j...@apache.org>
Subject [jira] Updated: (DERBY-1260) Investigate impact of infinite cost estimates on arithmetic operations/comparisons in the optimizer.
Date Mon, 29 Jun 2009 23:45:47 GMT

     [ https://issues.apache.org/jira/browse/DERBY-1260?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Dag H. Wanvik updated DERBY-1260:
---------------------------------

    Component/s: SQL

> 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
>          Components: SQL
>    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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