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https://issues.apache.org/jira/browse/DERBY-3818?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12619937#action_12619937
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Kristian Waagan commented on DERBY-3818:
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Insert performance is acceptable.
The problem is the select. We fetch the Clob piece by piece. Again we're hit by
the problem I tried to solve with DERBY-3769.
The limit for what we can transfer in one go is not 32672 characters, it seems
to be 32672 bytes. So Derby ends up advancing the stream too far, and has to
reset the stream and skip the data until correctly positioned again. Probably
we obtain a substring of 32672 characters, call String.getBytes(UTF8) and then
selects the first 32672 bytes of the resulting byte array. The rest is
discarded.
Data is going over the line as UTF-8.
The next problem hit is the naive repositioning algorithm, which we cannot
avoid by adjusting the buffer size. This is the same issue as for Blob
(DERBY-3766). I'll log a Jira for this, and maybe upload a patch for review
before I go on vacation.
I haven't spent a lot of time investigating this, but a simple experiment (with
some other unfinished code as well) brought the time on my machine down to 60
seconds, running both the embedded and the client suite.
> client Insert/retrieval of 18MB Clob is extremely slow in MultiByteClobTest
> -----------------------------------------------------------------------------
>
> Key: DERBY-3818
> URL: https://issues.apache.org/jira/browse/DERBY-3818
> Project: Derby
> Issue Type: Bug
> Components: JDBC, Network Client
> Affects Versions: 10.5.0.0
> Reporter: Kathey Marsden
>
> In the test memory.MultiByteClobTest that was added for DERBY-3741, the
> client version of the test took 525000ms vs 9578ms for embedded, so I
> disabled the client test for now. The client test should be analyzed to
> determine why Clob handling is so slow. I am not sure if the problem is on
> the insert, the retrieval or both. Once this issue is resolved it would be
> good to enable the test for client.
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