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From "Dag H. Wanvik (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (DERBY-6011) Derby performs very badly (seems to deadlock and timeout) in very simple multi-threaded tests
Date Mon, 07 Jan 2013 03:08:12 GMT

    [ https://issues.apache.org/jira/browse/DERBY-6011?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13545596#comment-13545596
] 

Dag H. Wanvik commented on DERBY-6011:
--------------------------------------

The threads are grabbing locks on rows in JOBQUEUE in different order (#17, 18), hence the
deadlock. Why they do, is the question to answer here. It could be the order in which the
application issues the queries, or the way the Derby executes them, possibly involving indexes.

Some questions: 

In this query, "SELECT id,status,checktime FROM jobqueue WHERE dochash=? AND jobid=? FOR UPDATE":

does this select a single row or multiple rows? If it is a single row, does the same thread's
transaction access multiple such rows, i.e. use multiple of these queries in the same transaction?.
If they do, are those accesses guaranteed to be in the same order (say, ascending on id)?.
Are there other SQL statements on JOBQUEUE that could require write locks on these row active
at this time?

                
> 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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