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From "Mike Matrigali (JIRA)" <j...@apache.org>
Subject [jira] Updated: (DERBY-3955) test lang/selectivity.sql can be revived
Date Tue, 24 Mar 2009 19:28:50 GMT

     [ https://issues.apache.org/jira/browse/DERBY-3955?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Mike Matrigali updated DERBY-3955:
----------------------------------


I am not sure what is going on here, but thought I would bring up the store part of this equation
-- which might make
sense of your test cases.
Store maintains an "estimated" row count of a table, it does not guarantee that it matches
the exact count of 
rows in the table and often it does not.  This count is updated either when the store thinks
the number has been
changed by 10% or when a dirty page leaves the cache.  So the number can vary depending on
what state the cache
is in before the test is run.

Note the counts I am talking about are the raw counts on the individual tables, where the
counts you are looking at
come from doing additional math on those numbers - that math is in the optimizer.

There are some points in the code where the sql layer of the system "knows" that it has just
done a scan of every
row in the table so it knows the exact count of the table and it updates the store's estimate
through a store interface.
I think this is triggered by a full index or base table scan.  But would be reasonable to
do a create index and update
statistic time also.  

I also believe creating an index after data is added to the table does the same thing as what
update statistics does, if
there is only one index on the table.  The cardinality statistics are only gathered on existing
indexes.

> test lang/selectivity.sql can be revived
> ----------------------------------------
>
>                 Key: DERBY-3955
>                 URL: https://issues.apache.org/jira/browse/DERBY-3955
>             Project: Derby
>          Issue Type: Test
>          Components: Test
>            Reporter: Myrna van Lunteren
>            Assignee: Kathey Marsden
>            Priority: Minor
>         Attachments: DERBY-3955.diff1, derby-3955_sanityCheck_dont_commit_diff.txt, oldSelectivity.java
>
>
> One test that was contributed during the IBM contribution of derby code was not runnable
at the time - lang/selectivity.sql.
> This test is still there, and I think might have some valuable regression tests if it
gets adapted to the current functionality in Derby.
> Ideally too, it should get converted to junit, or at least be made to run through the
langScripts junit suite.

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