[jira] Commented: (DERBY-3825) StoreStreamClob.getReader(charPos) performs poorly

["Kristian Waagan (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/DERBY-3825?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12637523#action_12637523 ] 

Kristian Waagan commented on DERBY-3825:
----------------------------------------

Just noticed I forgot the license header in the new test. I'll add it in the next rev.

> 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
>
>
> 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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