[jira] Commented: (DERBY-1160) Need a documented way to tell for tables and indexes: a) the number of pages allocated b) the number of empty pages

["Bryan Pendleton (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/DERBY-1160?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12785049#action_12785049 ] 

Bryan Pendleton commented on DERBY-1160:
----------------------------------------

I took a closer look at the output from SYSCS_DIAG.SPACE_TABLE, and I think it already
includes this information. See the references to NUMFREEPAGES and ESTIMSPACESAVING
in the description at
http://db.apache.org/derby/javadoc/engine/org/apache/derby/diag/SpaceTable.html

I tried running SYSCS_DIAG.SPACE_TABLE on a few sample tables, and it looks like
the output in these columns is legitimate.

So perhaps all that is needed here is to update the documentation for the compress
table discussion (http://db.apache.org/derby/docs/10.5/adminguide/cadminspace21579.html)
to provide some text suggesting that SPACE_TABLE can be used to estimate whether
a COMPRESS_TABLE is worth running?

> Need a documented way to tell for tables and indexes: a) the number of pages allocated  b) the number of empty pages
> --------------------------------------------------------------------------------------------------------------------
>
>                 Key: DERBY-1160
>                 URL: https://issues.apache.org/jira/browse/DERBY-1160
>             Project: Derby
>          Issue Type: Improvement
>          Components: SQL
>            Reporter: Stan Bradbury
>
> Very active systems would benefit from a documented way to determine how many empty pages are allocated to an index or table in order to determine whether a COMPRESS_TABLE is worth running.

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