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https://issues.apache.org/jira/browse/DERBY-3934?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Kristian Waagan updated DERBY-3934:
-----------------------------------
Attachment: derby-3934-4a-getinternalreader_cachedlength.diff
Patch 'derby-3934-4a-getinternalreader_cachedlength.diff' improves the
performance of Clob.getSubString when the Clob is represented by a
TemporaryClob.
The main change in the patch is the implementation of
TemporaryClob.getInternalReader(long).
The second important change is that TemporaryClob now caches the character
length. When the contents are changed, the length is either reset or updated
accordingly if possible.
I also added some length to verify that the length is correctly updated on Clob
modifications.
On my machine I see the following durations (one iteration) for
ClobAccessTest.testFetchLargeClobPieceByPieceModified:
trunk ~76'000 ms
with patch 4a ~600 ms
So with the patch the test completes in less than 1% of the time used by trunk.
This is saved CPU time.
Regressing tests are running.
Patch ready for review.
> Improve performance of reading modified Clobs
> ---------------------------------------------
>
> Key: DERBY-3934
> URL: https://issues.apache.org/jira/browse/DERBY-3934
> Project: Derby
> Issue Type: Improvement
> Components: JDBC
> Affects Versions: 10.5.0.0
> Reporter: Kristian Waagan
> Assignee: Kristian Waagan
> Attachments: derby-3934-1a-clob_replace_test.diff,
> derby-3934-2a-intclob_new_methods.diff,
> derby-3934-3a-clobupdreader_utf8reader.diff,
> derby-3934-3a-clobupdreader_utf8reader.stat,
> derby-3934-4a-getinternalreader_cachedlength.diff
>
>
> The performance of reading modified Clobs is poor, which is demonstrated by
> running a test program selecting a 10 MB Clob and then getting the contents
> using getSubString:
> - unmodified Clob (StoreStreamClob) : ~1 300 ms
> - modified Clob (TemporaryClob): ~156 000 ms
> In this case, the Clob was modified by changing the first character.
> A number of subtasks will be created to handle the various issues, which will
> be related to both performance and code cleanup.
> For a brief overview, see
> http://www.nabble.com/Suggestion-for-improving-ClobUpdatableReader-and-related-code-to20308303.html
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