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https://issues.apache.org/jira/browse/DERBY-3907?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12639080#action_12639080
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Kristian Waagan commented on DERBY-3907:
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[Upgrade issues]
Thanks for the information on the upgrade issue, Mike.
I think it sounds smart to follow existing patterns. Having never written this
type of code, I'll need some more time and more pieces of advice when I start
working on it.
So to sum it up (correct me if I got this wrong):
a) Support hard/soft upgrade
b) Use new format in new tables (in newly created databases and in hard
upgraded databases)
c) Leave data as it is at hard upgrade and support both formats for the
"stream header"
Is the format id stored per table only, or per row?
Besides from the lower level format id code, I see that changes must be done in
various other classes (i.e. ReaderToUTF8Stream and SQLClob).
I'm not sure, but I think some of the newly added classes (10.3 and later) must
be reviewed too, as they reset the stream to do positioning. Currently a reset
means to position the UTF-8 stream from store at position 2 to skip the two
length bytes.
> Save useful length information for Clobs in store
> -------------------------------------------------
>
> Key: DERBY-3907
> URL: https://issues.apache.org/jira/browse/DERBY-3907
> Project: Derby
> Issue Type: Improvement
> Components: JDBC, Store
> Affects Versions: 10.5.0.0
> Reporter: Kristian Waagan
> Assignee: Kristian Waagan
>
> The store should save useful length information for Clobs. This allows the
> length to be found without decoding the whole data stream.
> The following thread raised the issue on what information to store, and also
> contains some background information:
> http://www.nabble.com/Storing-length-information-for-CLOB-on-disk-tp19197535p19197535.html
> The information to store, and the exact format of it, is still to be
> discussed/determined.
> Currently two bytes are set aside for length information, which is inadequate.
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