[
https://issues.apache.org/jira/browse/DERBY-2822?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12643196#action_12643196
]
Knut Anders Hatlen commented on DERBY-2822:
-------------------------------------------
I think this patch is OK. It wasn't immediately clear to me that it was correct
to set the variable once and never update it or invalidate it, but it seems
like the StoreStreamClob object isn't changed when the underlying Clob changes,
even without your patch, so it looks safe to me.
> 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?
--
This message is automatically generated by JIRA.
-
You can reply to this email to add a comment to the issue online.
