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https://issues.apache.org/jira/browse/DERBY-6011?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13551418#comment-13551418
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Mike Matrigali commented on DERBY-6011:
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All the deadlocks I have seen listed are happening on page 1. The the dataset
particularly small? If so I often worry about the optimizer deciding not to
use the index in some cases as it figures out it can get all the rows by just
reading a page of the base table. I think we have checked query plans, but
sometimes they change with execution, especially now with automatic
statistics gathering. It is usually not a problem with real world data sets of
more than a page, but often shows up in test cases where the data set has been
made minimal.
A quick scan of the deadlocks posted seem to all be 2 rows that are one after
the other in the base table. Need to look at the data set to understand if
this relates to the rows being
one after the other in the index (ie. are the rows inserted in index order?).
If so, then previous key locking is likely involved.
To debug one could see if the deadlocks still appear if we enable the trace
that prints all query plans to the log on execution. Or if there are not too
many queries could use hints to force the use of the index
> Derby performs very badly (seems to deadlock and timeout) in very simple
> multi-threaded tests
> ---------------------------------------------------------------------------------------------
>
> Key: DERBY-6011
> URL: https://issues.apache.org/jira/browse/DERBY-6011
> Project: Derby
> Issue Type: Bug
> Affects Versions: 10.7.1.1, 10.8.2.2, 10.9.1.0
> Environment: Lenovo laptop with SSD's, Windows 7, 64-bit, Sun JDK
> 1.6.xx
> Reporter: Karl Wright
> Attachments: derby.log, manifoldcf.log
>
>
> The Apache ManifoldCF project supports Derby as one of its underlying
> databases. Simple tests, however, demonstrate that Derby is apparently
> deadlocking and timing out repeatedly under multi-thread conditions. This
> problem is long-standing, and is not exhibited by any other database
> ManifoldCF supports, and makes a simple test take between 6x and 12x as long.
> There is a trivial test with demonstrates the problem vs. other databases.
> Please do the following (once you have java 1.6+, svn 1.7+, and ant 1.7+
> available):
> (1) Check out https://svn.apache.org/repos/asf/manifoldcf/trunk
> (2) Run the following ant target to download the dependencies: "ant
> make-core-deps"
> (3) Run the Derby test: "ant run-rss-tests-derby" . Note the time required -
> at least 180 seconds, can be up to 360 seconds.
> (4) Run the equivalent HSQLDB test: "ant run-rss-tests-HSQLDB". This test
> takes about 31 seconds to run.
> The output of the Derby test can be found in the directory
> "tests/rss/test-derby-output". Have a look at manifoldcf.log, where all
> long-running queries are reported. Derby.log is also included, which shows
> only that during the test's cleanup phase the database is deleted before it
> is shutdown, which is not pertinent to the performance issue.
> I am available to assist with ManifoldCF, if that seems to be required.
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