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From Dyre.Tjeldv...@Sun.COM
Subject Re: FW: Advice on *very* badly performing query
Date Tue, 04 Dec 2007 17:56:19 GMT
Matt Doran <matt.doran@papercut.com> writes:

> That did it!!!  From 22 minutes down to less than a second.  :)
>
> I'm kinda embarassed that I didn't figure it myself.  

Don't be. It is not obvious.

> I had not idea
> that derby didn't keep any stats up-to-date without performing that
> operation explicitly.  Ideally it would keep this up-to-date itself.
> The sys.sysstatistics didn't have any rows in it until I ran the
> compress table operation.

Agreed, but strangely I cannot recall many users actually requesting
this. Maybe people just suffer silently? 

Anyway, thank you for what I would call an exemplary
bug-report/question! Even though you use Hibernate you took the time
to identfy the actual SQL causing the problem, identified a minimal
repro and provided query plans.

> It really needs to be made more prominent in the documentation.
> i.e. once your database is loaded with representative data, perform
> the compress op for optimal performance.

Agreed. Any thoughts on where it would be good to mention it? If
you want, you can file a Jira issue about this.

> In the mean-time, we've added a maintenance task to our application to
> do this operation periodically.

-- 
dt

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