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From Bryan Pendleton <bpendle...@amberpoint.com>
Subject Re: drop column functionality
Date Mon, 21 Aug 2006 17:07:13 GMT
> 1. Dropping the column seems very slow for large tables. 

This is good to know. I don't think anybody has really experimented with
this yet. Can you quantify "very slow" with some real measurements
you've taken? Do you think it would be reasonable to treat this as
a follow-on improvement to the DERBY-1489 changes, or do you feel that
the performance is so bad that DERBY-1489 is unusable as is?

I guess my assumption was that DROP COLUMN usage in large database
scenarios would be rare, and that it would be more common for people
to want to use DROP COLUMN during their initial application development,
when tables are typically smaller. But perhaps this is a bad assumption?

If you think this would be reasonable to treat as a follow-on
improvement, then please open a new JIRA issue for it, describe
it as well as you can with the data you can provide, and link
the new issue to DERBY-1489 so that we know they're related.

> 2. I'm reluctant to use the SVN trunk in my application, preferring a 
> stable release. Are there any plans for when this patch will get into a 
> stable release.

In general, I think the process is something like:
  - the community reviews the DERBY-1489 changes (that's underway now)
  - those changes get committed to the trunk
  - those changes could appear in future release branches, or could be
    back-ported to patch release of prior release branches.

I think we typically would *not* back-port a new feature to a prior
release branch, so the DERBY-1489 changes would probably next appear
in a stable release in the next release after they are committed to
the trunk.

However, I believe there's nothing that prevents you from constructing
this yourself. You can take the 10.1 source code, and apply the trunk
patch for DROP COLUMN to it, and create your own version of Derby which
is "10.1 with DROP COLUMN functionality". I believe that the DERBY-1489
changes can be successfully applied to the 10.1 source base without too
much work.

> 3. The version from trunk does not appear able to read databases created 
> with the release. Has the database file syntax changed?

I'm hoping one of the other developers can help with this question.
I think that this is on purpose, to avoid accidentally mixing releases
that may differ in major ways, but I think there is a configuration
flag that you can set that will authorize the trunk code to open and
read a previous-release database.

Can anybody help us out here? How can Tim use some of his 10.1 databases
in experimenting with a patched release built from the trunk?



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