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From "Knut Anders Hatlen (JIRA)" <j...@apache.org>
Subject [jira] Updated: (DERBY-4977) XPLAIN reports negative EXECUTE_TIME for some parts of a join
Date Tue, 18 Jan 2011 10:37:44 GMT

     [ https://issues.apache.org/jira/browse/DERBY-4977?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Knut Anders Hatlen updated DERBY-4977:
--------------------------------------

    Attachment: timing.sql

> XPLAIN reports negative EXECUTE_TIME for some parts of a join
> -------------------------------------------------------------
>
>                 Key: DERBY-4977
>                 URL: https://issues.apache.org/jira/browse/DERBY-4977
>             Project: Derby
>          Issue Type: Bug
>          Components: SQL
>    Affects Versions: 10.7.1.1
>            Reporter: Knut Anders Hatlen
>            Priority: Minor
>         Attachments: timing.sql
>
>
> I see that if I execute a join against the system tables with XPLAIN and statistics timing
enabled, some of the rows in SYSXPLAIN_RESULTSET_TIMINGS have negative values in the EXECUTE_TIME
column.
> Here are the contents of the SYSXPLAIN_RESULTSET_TIMINGS after two runs with the attached
repro script:
> ij> select execute_time from my_schema.sysxplain_resultset_timings;
> EXECUTE_TIME        
> --------------------
> -1                  
> 0                   
> 0                   
> -6                  
> 9                   
> 16                  
> 6 rows selected
> ij> select execute_time from my_schema.sysxplain_resultset_timings;
> EXECUTE_TIME        
> --------------------
> -1                  
> 1                   
> 0                   
> -7                  
> 10                  
> 15                  
> 6 rows selected
> Note the two rows with negative values in both of the examples.

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