[ http://issues.apache.org/jira/browse/DERBY-125?page=all ]
Bryan Pendleton updated DERBY-125:
----------------------------------
Attachment: svn_jan_22_2006.diff
Attached is the latest patch proposal, updated to the latest trunk,with all
conflicts resolved and derbyall passing. There are two changes in this patch
proposal relative to the previous one:
- I've changed the regression test to use the new test devised by Army. I've
verified that the test fails before the patch to DDMWriter, and succeeds after
it. Although I agree that the test is a bit delicate, it is much better to have
a test which clearly demonstrates the problem.
- I've improved the comments in finalizeDssLength() a bit to explain my
changes a bit better, and also included a pointer to this bug report for those
future historians who desire to study the bug in more detail.
Kathey, Dyre, Army: thank you very much for your feedback on the previous
proposals and on the questions I raised. My preference is to treat your
suggestions independently, and to open separate JIRA entries to track resolving
these questions in the future:
- Improving DDMWriter traces to make them easier to read in the presence of
continuations and chaining
- Modifying the client to process the length portion of DSS Continuation
Headers, compatibly with previous releases
- Under SanityManager control, pre-filling the DDMWriter buffer with special
non-zero data to reveal memory corruption problems more readily
- Investigating performance issues in large object handling with respect to
both memory usage and number of data copies
Thanks again to everybody who has helped me with the investigations into this
bug.
> Network Server can send DSS greater than 32K to client, which breaks DRDA
> protocol.
> -----------------------------------------------------------------------------------
>
> Key: DERBY-125
> URL: http://issues.apache.org/jira/browse/DERBY-125
> Project: Derby
> Type: Bug
> Components: Network Server
> Reporter: A B
> Assignee: Bryan Pendleton
> Attachments: changes.html, offByOne.jar, repro.java, svn_jan_12_2006.status,
> svn_jan_22_2006.diff
>
> BACKGROUND:
> DRDA protocol, which is the protocol used by Derby Network Server, dictates
> that all DSS objects "with data greater than 32,763 bytes" should be broken
> down into multiple "continuation" DSSes.
> PROBLEM:
> When Network Server receives a "prepareStatement" call that has a very large
> number of parameters, it can end up sending a reply DSS that is greater than
> 32K long to the client; doing so breaks DRDA protocol.
> REPRODUCTION:
> Note that this reproduction does NOT cause a protocol exception against the
> JCC driver--without further investigation, it would appear JCC doesn't mind
> that the DSS is too long. However, other DRDA clients (such as the DB2 ODBC
> client) will see that the data is too long and will fail because of it.
> To reproduce, one can create a simple table and then prepare a statement such
> as:
> SELECT id FROM t1 WHERE id in ( ?, ?, [ ... lots and lots of param markers
> ... ], ?)
> Note that JCC uses deferred prepare by default; when connecting, one must
> append the "deferPrepares=false" attribute to the end of the URL in order to
> reproduce the problem (that or just try to execute the statement, since
> preparation will be done at execution time). When doing the prepare, I added
> a line in the "flush" method of org.apache.derby.impl.drda.DDMWriter.java to
> see how large the reply DSS was, and for cases where the number of parameter
> markers was high, the number of bytes in the single DSS would surpass 32K,
> and thus break protocol.
> NOTES:
> Network Server correctly uses continuation DSSes for LOBs and for result set
> data (data returned as the result of a query) that is greater than 32K. The
> problem appears to be in "other" cases, such as for the prepareStatement call
> described above.
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