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From Manjula G Kutty <manjula.ku...@gmail.com>
Subject Re: How do I tell whether a table has unused space or not?
Date Tue, 28 Mar 2006 19:44:23 GMT
Bryan Pendleton wrote:

> Recently, I had a table which was able to substantially
> benefit from compression. I determined that I had a problem
> by setting derby.logQueryPlan to TRUE, running a "select *"
> query against the table, and then viewing the page and
> row count statistics that were emitted in the query plan,
> where I saw that the optimizer was expecting to process many
> more pages than I thought needed to be in the table.
> Compressing the table made my problem go away, and the
> optimizer returned to choosing my desired query plans.
> But I am left with the desire for an easier way to figure
> out whether my table needs compression or not.
> I tried reading the manual, for example I found
> http://db.apache.org/derby/docs/10.1/adminguide/cadminspace21579.html
> but that page does not offer any clear way to tell whether a
> table needs to be compressed or not.
> What is the preferred way to decide whether a table has unused space?
> thanks,
> bryan
Hi Bryan,

I don't know this info will be useful for you or not. But in my case I 
used compress when i happen to see that even if I delete rows I'm not 
getting any space back. This was happening in my test where I kept the 
number of rows in the table to be more or less same by doing inserts and 
deletes. The db size kept on increasing, even though I was doing the 
deletes. Mike's fix for the jira issue 670 and the use of inplace 
compression solved most of the problem


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