Investigate impact of infinite cost estimates on arithmetic
operations/comparisons in the optimizer.
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Key: DERBY-1260
URL: http://issues.apache.org/jira/browse/DERBY-1260
Project: Derby
Type: Task
Components: Performance
Versions: 10.2.0.0
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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