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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-3825-0a-preview.diff
'derby-3825-0a-preview.diff' is a preview patch. It is incomplete and not for
commit.
It introduces a new method for InternalClob: getInternalReader(charPos).
The idea is to keep only one such reader per clob that can be used internally -
that is not published to the user. The most prominent example is
Clob.getSubString().
There are two performance gains:
1) Repositioning capabilities (see below).
2) Less object creation (GC).
The repositioning functionality is added to UTF8Reader, and can be split into
three types - ordered after increasing cost:
a) Reposition within current character buffer (small hops forwards and
potentially backwards - in range 1 char to 8K chars)
b) Forward stream from current position (hops forwards)
c) Reset stream and skip data (hops backwards)
The more I work with this, the more I feel the functionality should be pushed
closer to store.
Preview patch ready for comments.
> 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
> Attachments: derby-3825-0a-preview.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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