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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 closed DERBY-3825.
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Closing the issue.
Note that getReader is still rather low-performant, compared to what it could
have been. Again the cause is positioning. The trick I used for
getInternalReader cannot be used, because the reader from getReader is passed
out to the user and cannot be shared.
Given the current requirements and limitations, a possible optimization is to
remember one or more byte/char position and then be able to skip bytes instead
of chars. The latter requires decoding, the former doesn't.
On the other side, if a user just obtains one reader and keeps reading from it,
the initial positioning cost doesn't matter that much.
The problem with getSubString has been resolved by the patches committed.
> 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
> Fix For: 10.4.2.1, 10.5.0.0
>
> 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,
> derby-3825-3a-simplification.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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