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From "Mamta A. Satoor (JIRA)" <j...@apache.org>
Subject [jira] Commented: (DERBY-3788) Provide a zero-admin way of updating the statisitcs of an index
Date Mon, 01 Dec 2008 19:35:44 GMT

    [ https://issues.apache.org/jira/browse/DERBY-3788?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12652114#action_12652114
] 

Mamta A. Satoor commented on DERBY-3788:
----------------------------------------

My understanding of DERBY-3892 is as follows
1)A query is exectued and the best plan for it is picked up based on the current data in the
database
2)The data changes quite a bit which makes the plan chosen for the query not an optimal plan
but during the next execution of the query, we continue to use the plan chosen in step 1).


Based on the above understanding of DERBY-3892, the current work going on for DERBY-3788 is
not going to fix DERBY-3892. This jira entry will go and build the statistics if during the
query compilation it is found that the required statistics do not exist. Hope this answers
your question about DERBY-3892, Dag.

> Provide a zero-admin way of updating the statisitcs of an index
> ---------------------------------------------------------------
>
>                 Key: DERBY-3788
>                 URL: https://issues.apache.org/jira/browse/DERBY-3788
>             Project: Derby
>          Issue Type: New Feature
>          Components: Performance
>    Affects Versions: 10.5.0.0
>            Reporter: Mamta A. Satoor
>            Assignee: Mamta A. Satoor
>         Attachments: DERBY3788_patch1_diff.txt, DERBY3788_patch1_stat.txt, DERBY3788_patch2_diff.txt,
DERBY3788_patch2_stat.txt, DERBY_3788_Mgr.java, DERBY_3788_Repro.java
>
>
> DERBY-269 provided a manual way of updating the statistics using the new system stored
procedure SYSCS_UTIL.SYSCS_UPDATE_STATISTICS. It will be good for Derby to provide an automatic
way of updating the statistics without requiring to run the stored procedure manually. There
was some discussion on DERBY-269 about providing the 0-admin way. I have copied it here for
reference.
> *********************
> Kathey Marsden - 22/May/05 03:53 PM 
> Some sort of zero admin solution for updating statistics would be prefferable to the
manual 'update statistics' 
> *********************
> *********************
> Mike Matrigali - 11/Jun/08 12:37 PM 
> I have not seen any other suggestions, how about the following zero admin solution? It
is not perfect - suggestions welcome. 
> Along with the statistics storing, save how many rows were in the table when exact statistics
were calculated. This number is 0 if none have been calculated because index creation happened
on an empty table. At query compile time when we look up statistics we automatically recalculate
the statistics at certain threshholds - say something like row count growing past next threshhold
: 10, 100, 1000, 100000 - with upper limit being somewhere around how many rows we can process
in some small amount of time - like 1 second on a modern laptop. If we are worried about response
time, maybe we background queue the stat gathering rather than waiting with maybe some quick
load if no stat has ever been gathered. The background gathering could be optimized to not
interfere with locks by using read uncommitted. 
> I think it would be useful to also have the manual call just to make it easy to support
customers and debug issues in the field. There is proably always some dynamic data distribution
change that in some case won't be picked up by the automatic algorithm. Also just very useful
for those who have complete control of the create ddl, load data, run stats, deliver application
process. 
> *********************

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