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From "Kristian Waagan (JIRA)" <j...@apache.org>
Subject [jira] Updated: (DERBY-3825) StoreStreamClob.getReader(charPos) performs poorly
Date Wed, 06 Aug 2008 14:42:44 GMT

     [ https://issues.apache.org/jira/browse/DERBY-3825?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel

Kristian Waagan updated DERBY-3825:

    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:
>            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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