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https://issues.apache.org/jira/browse/DERBY-3825?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Kristian Waagan updated DERBY-3825:
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Attachment: derby-3825-2b-internalReader_repositioning.diff
Patch 2b addresses the following:
- added license to UTF8ReaderTest
- changed class comment in UTF8ReaderTest
- added DEBUG block with detailed EOFException
Regarding Knut Anders' comments (from top to bottom):
- Thanks for looking at the repositioning logic. It is a bit complex, but it
should be pretty well tested functionally. Can it be optimized?
- Regarding the poor performance you observed, I need to look into it. I will
create a new Jira for it. Implementing getInternalReader is one issue, but I
think there are more severe problems in this code path (it is using some
special reader objects). Hopefully the ClobAccessTest should demonstrate the
problem.
- I resolved the localization issue by throwing a detailed EOFException from
inside a debug block. I chose this over an assert, as an assert makes a test
fail (expects EOFException).
- I changed the comment, it was not very precise. I need a package-private
test because of StoreStreamClob, which is the only user of
UTF8Reader.reposition at the moment and I wanted a little bit more control than
what I get going through the JDBC API.
Thanks for looking at the patch!
Unless there are more comments on patch 2b, I expect to commit it shortly.
> StoreStreamClob.getReader(charPos) performs poorly
> --------------------------------------------------
>
> Key: DERBY-3825
> URL: https://issues.apache.org/jira/browse/DERBY-3825
> Project: Derby
> Issue Type: Bug
> Components: JDBC, Store
> Affects Versions: 10.5.0.0
> Reporter: Kristian Waagan
> Assignee: Kristian Waagan
> Attachments: derby-3825-0a-preview.diff,
> derby-3825-1a-reset_readpositioninbuffer.diff,
> derby-3825-2a-internalReader_repositioning.diff,
> derby-3825-2a-internalReader_repositioning.stat,
> derby-3825-2b-internalReader_repositioning.diff
>
>
> StoreStreamClob.getReader(charPos) performs poorly because it resets the
> underlying stream and skips data until it reached the requested character
> position. Not only does the data has to be skipped, it also has to be decoded
> (UTF-8).
> The problem is exposed through EmbedClob.getSubString, which causes extremely
> bad performance for the client driver because the locator based Clob
> implementation uses this method.
> For the record, there is another read buffer size issue that exaggerates the
> problem (it will probably be handled under DERBY-3769, and also DERBY-3818).
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