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https://issues.apache.org/jira/browse/DERBY-4241?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12717241#action_12717241
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Kristian Waagan commented on DERBY-4241:
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Committed patch 1a to trunk with revision 782600.
I'll wait a few more days with patch 2a, hoping that someone will have a look
at it.
> Improve transition from read-only to writable Clob representation
> -----------------------------------------------------------------
>
> Key: DERBY-4241
> URL: https://issues.apache.org/jira/browse/DERBY-4241
> Project: Derby
> Issue Type: Sub-task
> Components: JDBC
> Affects Versions: 10.5.1.1, 10.6.0.0
> Reporter: Kristian Waagan
> Assignee: Kristian Waagan
> Priority: Minor
> Attachments: derby-4241-1a-InternalClob.getLengthIfKnown.diff,
> derby-4241-2a-utf8AwareCopy.diff
>
>
> When a store stream Clob is going to be modified, it will be written out to
> the temporary area of Derby and represented as a TemporaryClob.
> The transfer of the data is done in a sub-optimal manner for two reasons;
> o for transfer of the complete Clob, the copy method operates on the byte
> level and we're not able to save the character length.
> o for transfer of parts of the Clob (i.e. truncation), we have to first
> decode the UTF-8 encoding to find the byte count and then transfer the same
> bytes.
> I intend to do the following two changes;
> 1) Add a getCharLengthIfKnow-method to InternalClob.
> 2) Add a UTF-8 aware copy method to LOBStreamControl.
> When a complete Clob is to be copied, code like this will be executed;
> cachedCharLength = internalClob.getLengthIfKnown();
> if (cachedCharLength > 0)
> // use existing byte-oriented copy method for best performance (copy
> until EOF)
> else
> cachedCharLength = control.copyUTF8Data()
> When parts of a Clob is to be copied, we always use the UTF-8 aware copy
> method, but we also do a cheap range check.
> cachedCharLength = internalClob.getLengthIfKnown();
> if (cachedCharLength > 0 && requestedLength > cachedCharLength)
> throw EOFException();
> if (cachedCharLength == requestedLength)
> // use existing byte-oriented copy method for best performance (copy
> until EOF)
> else
> cachedCharLength = control.copyUTF8Data(requestedLength);
> Adding the UTF-8 aware copy method was started under DERBY-4023, including
> comments on the first revision of a patch.
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