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Posted to derby-dev@db.apache.org by "Mamta A. Satoor (JIRA)" <ji...@apache.org> on 2013/06/25 07:06:23 UTC
[jira] [Updated] (DERBY-1906) Investigate appropriateness of
current optimizer timeout mechanism.
[ https://issues.apache.org/jira/browse/DERBY-1906?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Mamta A. Satoor updated DERBY-1906:
-----------------------------------
Urgency: Normal
Labels: derby_triage10_11 (was: )
> Investigate appropriateness of current optimizer timeout mechanism.
> -------------------------------------------------------------------
>
> Key: DERBY-1906
> URL: https://issues.apache.org/jira/browse/DERBY-1906
> Project: Derby
> Issue Type: Task
> Components: SQL
> Affects Versions: 10.1.3.2, 10.2.1.6, 10.3.1.4
> Reporter: A B
> Labels: derby_triage10_11
>
> The Derby optimizer timeout mechanism is based on the assumption that cost estimates calculated by the optimizer represent the number of milliseconds the optimizer thinks it will take for the query to execute. In order for this to be effective the cost estimates need to be relatively accurate--or else, as described in DERBY-1905, the timeout mechanism becomes pretty ineffective pretty quickly.
> While it is true that incorrect cost estimates are perhaps the biggest cause of inefficient optimizer timeout, I can't help but wonder if there might be some other way to handle optimizer timeout that is not so dependent on the correctness of a costEstimate-to-milliseconds mapping. Maybe, for example, an algorithm based on delta's between query plan cost estimates would be more appropriate?
> I do not know what alternatives exist or which, if any, would be more "right" for Derby than a millisecond-based approach, but I think it's worth searching out and/or coming up with algorithms/ideas that might prove more effective for Derby optimizer timeout--especially when dealing with very deeply-nested queries that have large FROM lists, such as those attached to DERBY-1777.
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