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From Rick Hillegas <Richard.Hille...@Sun.COM>
Subject Re: What happens during a database upgrade?
Date Wed, 27 May 2009 13:35:05 GMT
David Goulden wrote:
> Good day,
> We would like to update our derby version from to due to
> the newer version's much improved performance with large CLOBS. However our
> client is very conservative and would like to be sure the upgrade won't
> cause any issues.
> Can anyone tell me what changes are made to a database when derby performs
> an upgrade? What is the best way to verify that the upgrade hasn't caused
> any changes to the data?
> Many thanks,
> David
Hi David,

The 10.4 -> 10.5 upgrade changes some of the system metadata on disk but 
does not alter any user data. However, if you yourself rewrite your 
CLOBs after the upgrade, the on disk format will change. That is because 
10.5 adds some extra header information to on disk CLOBs in order to 
deliver the performance improvements you want. I don't believe that you 
will see the performance improvements until you update your CLOBs yourself.

You might try the following experiment:

1) Copy your 10.4 database to a temporary location.

2) Hard-upgrade that copy.

3) Rewrite a couple of your CLOBs by, for example, using a vacuous 
update statement:

    update myTable set clobColumn = clobColumn where keyColumn = ?

4) Verify that you are seeing better performance for the CLOBs you have 
rewritten. Also verify that your application still functions properly on 
those CLOBs.

Kristian, who improved CLOBs for 10.5, may want to comment further.

Hope this helps,

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