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https://issues.apache.org/jira/browse/DERBY-3788?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12649820#action_12649820
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Mamta A. Satoor commented on DERBY-3788:
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Thanks again for your time, Knut. I will try to address some of the questions
in this comment. I am planning on taking next week as vacation so will get back
on this task after that.
1)In this jira entry, missing statisitcs will be detected when the user
executes a select. I had originally just for the sake of trying attempted to
create the statistics in the select thread when I find that the statistics are
missing. But executing an update inside of a select processing caused problem
because data dictionary was not in write mode. Because of that, I couldn't
update the statistics during the select processing. One very simple example
where one will find missing statistics is as follows
create table t1 (c11 int, c12 char);
create index i1 on t1(c11);
insert into t1 values (1,'1'),(2,'2'),(3,'3');
select * from sys.sysstatistics;
My goal is to fire the statistics in background when user executes say
following sql
select * from t1 where c11=1;
2)As for the calls to setting the context and unsetting, I think you are right.
I will remove them and see how it goes.
> 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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