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https://issues.apache.org/jira/browse/DERBY-2634?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12495004
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Frank-Ralph Reiser commented on DERBY-2634:
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I just replaced the subselects with equivalent left joins, same results:
ResultSet.next() takes appr. 40ms without any cpu load.
> CLOB performance partially very poor on linux system
> ----------------------------------------------------
>
> Key: DERBY-2634
> URL: https://issues.apache.org/jira/browse/DERBY-2634
> Project: Derby
> Issue Type: Improvement
> Components: Network Client, Network Server, Performance
> Affects Versions: 10.2.2.0, 10.3.0.0
> Environment: gnu linux, network client and network server on the same
> machine
> Reporter: Frank-Ralph Reiser
> Attachments: derbytest-linux-laptop-1.66GHz.txt, testcase.zip
>
>
> Doing some performance tests with several differente database
> implementations, we noticed very poor query performance of apache derby under
> certain conditions.
> If the select statement selects a CLOB column and if it contains a subselect,
> traversing the ResultSet takes very long with nearly no cpu load.
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