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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