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From "A B (JIRA)" <j...@apache.org>
Subject [jira] Commented: (DERBY-2641) Convert lang/staleplans.sql to JUnit
Date Tue, 15 May 2007 16:44:16 GMT

    [ https://issues.apache.org/jira/browse/DERBY-2641?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12496049
] 

A B commented on DERBY-2641:
----------------------------

> I would say it is reasonable to expect a table scan in these cases since the table only
contains one row, but
> I don't know enough about this area to say whether it's a bug. If someone thinks it's
a bug, I will file a JIRA
> for it.

I took a quick look at this and noticed the following comment in the "estimateCost(...)" method
of FromBaseTable:

    /* we prefer index than table scan for concurrency reason, by a small
     * adjustment on estimated row count.  This affects optimizer's decision
     * especially when few rows are in table. beetle 5006. This makes sense
     * since the plan may stay long before we actually check and invalidate it.
     * And new rows may be inserted before we check and invalidate the plan.
     * Here we only prefer index that has start/stop key from predicates. Non-
     * constant start/stop key case is taken care of by selectivity later.
     */

I think this why the optimizer is choosing an index scan.  It seems intentional, so my guess
is that this is *not* a bug.  Probably the case that the comments in statelplans.sql were
not updated when the above comment (and associated code) was added...?

> Convert lang/staleplans.sql to JUnit
> ------------------------------------
>
>                 Key: DERBY-2641
>                 URL: https://issues.apache.org/jira/browse/DERBY-2641
>             Project: Derby
>          Issue Type: Improvement
>          Components: Test
>    Affects Versions: 10.3.0.0
>            Reporter: Knut Anders Hatlen
>         Assigned To: Knut Anders Hatlen
>            Priority: Minor
>         Attachments: derby-2641-1.diff, derby-2641-1.stat
>
>


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