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From "Mamta A. Satoor (JIRA)" <j...@apache.org>
Subject [jira] Commented: (DERBY-269) Provide some way to update index cardinality statistics (e.g. reimplement update statistics)
Date Mon, 14 Jul 2008 21:32:31 GMT

    [ https://issues.apache.org/jira/browse/DERBY-269?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12613458#action_12613458
] 

Mamta A. Satoor commented on DERBY-269:
---------------------------------------

I spent time looking through selectivity.sql and tried converting the test cases into just
a sql file where we do not rely on the old functionality which is not supported anymore. The
existing selectivity.sql depends on the features like Object.methods eg runtimestatistics().rts.getEstimatedRowCount(),
runtimestatistics().getScanStatisticsText('TEMPLATE') inside of sql. 
eg
create view showstats as
select cast (conglomeratename as varchar(20)) indexname, 
	   cast (statistics.toString() as varchar(40)) stats,
	   creationtimestamp createtime, 
	   colcount ncols
from sys.sysstatistics, sys.sysconglomerates 
where conglomerateid = referenceid;

Such object lookup is not available in Derby. I will spend more time on it but it may not
work out with the curent Derby functionality.

I was wondering if community had any ideas/test cases which I can use for the new stored procedure.
I can do basic testing which shows that the stored procedure runs etc but it will be nice
to see the real impact of running the stored procedure on a query before and after the update
statistics runs. Thanks for any help with this.


> Provide some way to update index cardinality statistics (e.g. reimplement update statistics)
> --------------------------------------------------------------------------------------------
>
>                 Key: DERBY-269
>                 URL: https://issues.apache.org/jira/browse/DERBY-269
>             Project: Derby
>          Issue Type: New Feature
>          Components: SQL
>    Affects Versions: 10.0.2.0, 10.0.2.1, 10.1.1.0, 10.2.2.0, 10.3.1.4
>            Reporter: Stan Bradbury
>            Assignee: Mamta A. Satoor
>         Attachments: DERBY269_update_statistics_svndiff_ver1.txt, DERBY269_update_statistics_svnstat_ver1.txt
>
>
> Performance problems are being reported that can be resolved by updating the cardinality
statistics used by the optimizer.  Currently the only time the statistics are guaranteed to
be an up-to-date is when the index is first created on a fully populated table.  This is most
easily accomplished on an existing table by using the command: 
>    alter table <table-name> compress [sequential]  
> Compress table is an I/O intensive task.  A better way to achieve this would be to re-enable
parser support for the 'update statistics' command or re-implement the update in some other
fashion.

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