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From "Kristian Waagan (JIRA)" <j...@apache.org>
Subject [jira] Commented: (DERBY-3907) Save useful length information for Clobs in store
Date Mon, 13 Oct 2008 15:34:44 GMT

    [ https://issues.apache.org/jira/browse/DERBY-3907?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12639080#action_12639080

Kristian Waagan commented on DERBY-3907:

[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:
>            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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