[jira] Commented: (DERBY-3788) Provide a zero-admin way of updating the statisitcs of an index

["Mamta A. Satoor (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/DERBY-3788?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12621910#action_12621910 ] 

Mamta A. Satoor commented on DERBY-3788:
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I am looking to see if the statistics do not exist for an index during a query compile phase, then try to create them while compiling the query. But trying to create statistics during query compilation throw following exception. 
ERROR XCL21: You are trying to execute a Data Definition statement (CREATE, DROP, or ALTER) while preparing a different statement. This is not allowed. It can happen if you execute a Data Definition statement from within a static initializer of a Java class that is being used from within a SQL statement.

The exception is being thrown from DataDictionaryImpl.startWriting(LanguageConnectionContext) through following piece of code
/*
** Don't allow DDL if we're binding a SQL statement.
*/
if (lcc.getBindCount() != 0)
{
throw StandardException.newException(SQLState.LANG_DDL_IN_BIND);
}

My question is can we disable this say when statistics are getting updated while a query is getting executed? Is there any other way of achieving creating statistics on fly when we know that we are going to need them during the execution of the current query? Appreciate any feedack.

> 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
>
> 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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