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From "Harshvardhan Gupta (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (DERBY-6940) Enhance derby statistics for more accurate selectivity estimates.
Date Wed, 21 Jun 2017 19:20:00 GMT

     [ https://issues.apache.org/jira/browse/DERBY-6940?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Harshvardhan Gupta updated DERBY-6940:
--------------------------------------
    Description: 
Derby should collect extra statistics during index build time, statistics refresh time which
will help optimizer make more precise selectivity estimates and chose better execution paths.

We eventually want to utilize the new statistics to make better selectivity estimates / cost
estimates that will help find the best query plan. Currently Derby keeps two type of stats
- the total row count and the number of unique values.

We are initially extending the stats to include null count, the minimum value and maximum
value associated with each of the columns of an index. This would be useful in selectivity
estimates for operators such as [ IS NULL, <, <=, >, >= ] , all of which currently
rely on hardwired selectivity estimates.

  was:Derby should collect extra statistics during index build time, statistics refresh time
which will help optimizer make more precise selectivity estimates and chose better execution
paths.


> Enhance derby statistics for more accurate selectivity estimates.
> -----------------------------------------------------------------
>
>                 Key: DERBY-6940
>                 URL: https://issues.apache.org/jira/browse/DERBY-6940
>             Project: Derby
>          Issue Type: Sub-task
>          Components: SQL
>            Reporter: Harshvardhan Gupta
>            Assignee: Harshvardhan Gupta
>            Priority: Minor
>         Attachments: DERBY-6940_2.diff, DERBY-6940_3.diff, derby-6940.diff
>
>
> Derby should collect extra statistics during index build time, statistics refresh time
which will help optimizer make more precise selectivity estimates and chose better execution
paths.
> We eventually want to utilize the new statistics to make better selectivity estimates
/ cost estimates that will help find the best query plan. Currently Derby keeps two type of
stats - the total row count and the number of unique values.
> We are initially extending the stats to include null count, the minimum value and maximum
value associated with each of the columns of an index. This would be useful in selectivity
estimates for operators such as [ IS NULL, <, <=, >, >= ] , all of which currently
rely on hardwired selectivity estimates.



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