[jira] Commented: (DERBY-737) SYSCS_UTIL.SYSCS_COMPRESS_TABLE should create statistics if they do not exist

["Mike Matrigali (JIRA)" <de...@db.apache.org>]

    [ http://issues.apache.org/jira/browse/DERBY-737?page=comments#action_12359669 ] 

Mike Matrigali commented on DERBY-737:
--------------------------------------

I don't see any downside to creating the statistics whether they exist or not.  Not sure why the distinction was made.  
First try at this might be just removing the if in opensource/java/engine/org/apache/derby/impl/sql/execute/AlterTableConstantAction.java!updateIndex():

            if (td.statisticsExist(cd))
            {
                cCount = new CardinalityCounter(tc.openSortRowSource(sortIds[ind
ex]));
                updateStatistics = true;
            }
            else
                cCount = tc.openSortRowSource(sortIds[index]);


But life is probably not that easy.  Likely there is slightly more work to create the statistics row vs. updating it.  The work to insert the row can be
found in: 
opensource/java/engine/org/apache/derby/impl/sql/execute/CreateIndexConstantAction.java

> SYSCS_UTIL.SYSCS_COMPRESS_TABLE should create statistics if they do not exist
> -----------------------------------------------------------------------------
>
>          Key: DERBY-737
>          URL: http://issues.apache.org/jira/browse/DERBY-737
>      Project: Derby
>         Type: Improvement
>   Components: SQL
>     Versions: 10.0.2.0, 10.0.2.1, 10.1.1.0, 10.1.1.1, 10.1.1.2, 10.1.2.0, 10.1.2.1, 10.2.0.0, 10.1.3.0, 10.1.2.2, 10.0.2.2
>     Reporter: Kathey Marsden
>     Priority: Minor

>
> There must be an entry in the SYSSTATISTICS table in order for the cardinality statistics in SYSSTATISTICS to be created with SYSCS_UTIL.SYSCS_COMPRESS_TABLE 
> SYSCS_UTIL.SYSCS_COMPRESS_TABLE  should create statistics if they don't exist.  The only way to create them if the index was created on an empty table, seems to be to drop and recreate the index after the table has been loaded.
> The documentation will also need updating if this change is made.
> http://db.apache.org/derby/docs/10.1/tuning/ctunstats57373.html

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