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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 Tue, 20 Jun 2017 16:37:00 GMT

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

Harshvardhan Gupta updated DERBY-6940:
    Attachment: DERBY-6940_2.diff

I am attaching an updated diff which now collects extra statistics whenever an index is created
/ altered. There are 3 ways for statistics update - 

1) Creating a new index.
2) Altering an Index.
3) Explicitly calling SYSCS_UPDATE_STATISTICS system procedure.

The current patch collects statistics in all the above cases. I am currently working on upgrade
logic post which we can look at ways to utilise the extra statistics in selectivity estimates.

While a soft upgrade can be performed by turning off extra statistics collection and turning
off reading and writing to store. However, we can go about multiple ways regarding the hard
upgrade strategy.

Options - 
1) We update all the existing indexes and add extra statistics during upgrade time.
2) We wait for user to explicitly call UPDATE_STATISTICS / Alter index system procedure before
collecting and writing to store extra statistics.

I would like to know what the community thinks is the best way, also please share if you have
any other strategy in mind.

> 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.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

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