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From "Kristian Waagan (JIRA)" <j...@apache.org>
Subject [jira] Updated: (DERBY-2822) Add caching of store stream length in StoreStreamClob, if appropriate
Date Tue, 26 Aug 2008 14:44:44 GMT

     [ https://issues.apache.org/jira/browse/DERBY-2822?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Kristian Waagan updated DERBY-2822:
-----------------------------------

            Priority: Major  (was: Minor)
    Derby Categories: [Performance]

Increasing priority, as this issue may severely reduce performance.
As far as I can see, both user code and internal Derby code would benefit from caching the
length.

For instance, Clob.setString in the client driver causes the length to be obtained for validating
the input from the user. Worst case scenario is that ~2G characters are skipped to insert
one char.

> Add caching of store stream length in StoreStreamClob, if appropriate
> ---------------------------------------------------------------------
>
>                 Key: DERBY-2822
>                 URL: https://issues.apache.org/jira/browse/DERBY-2822
>             Project: Derby
>          Issue Type: Improvement
>          Components: JDBC
>    Affects Versions: 10.3.1.4
>            Reporter: Kristian Waagan
>         Attachments: derby-2822-1a-cacheCharLength.diff
>
>
> Currently StoreStreamClob reads the whole Clob stream, including decoding it, to find
the length of it. It also does this the second time the length is asked for.
> StoreStreamClob is the internal Clob representation for Clobs that are read-only. As
soon as the user updates the Clob, it is transferred to a modifiable Clob representation.
> It should be determined if it is safe to cache the length (both in bytes and in characters)
of the store stream to improve the performance and reduce the load on Derby for certain Clob
operations.
> To do this, the locking mechanism used for Clobs must be analyzed.
> If you have obtained a Clob object, is there a lock in place that stops others from changing
the content?
> For all isolation levels?
> What about scrollable result sets?
> Can the streamed content from store be changed under us, and thus invalidate a cached
length?

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