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From "Kristian Waagan (JIRA)" <j...@apache.org>
Subject [jira] Created: (DERBY-2822) Add caching of store stream length in StoreStreamClob, if appropriate
Date Thu, 14 Jun 2007 22:21:26 GMT
Add caching of store stream length in StoreStreamClob, if appropriate
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                 Key: DERBY-2822
                 URL: https://issues.apache.org/jira/browse/DERBY-2822
             Project: Derby
          Issue Type: Improvement
          Components: JDBC
    Affects Versions: 10.3.0.0
            Reporter: Kristian Waagan
            Priority: Minor


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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