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From "Chris Wilson (JIRA)" <j...@apache.org>
Subject [jira] Created: (DERBY-4620) Query optimizer causes OOM error on a complex query
Date Sun, 18 Apr 2010 13:20:25 GMT
Query optimizer causes OOM error on a complex query
---------------------------------------------------

                 Key: DERBY-4620
                 URL: https://issues.apache.org/jira/browse/DERBY-4620
             Project: Derby
          Issue Type: Bug
          Components: SQL
    Affects Versions: 10.5.3.0
         Environment: java version "1.6.0_17"
Java(TM) SE Runtime Environment (build 1.6.0_17-b04)
Java HotSpot(TM) Client VM (build 14.3-b01, mixed mode, sharing)
Linux rocio.xxx 2.6.24-27-generic #1 SMP Fri Mar 12 01:10:31 UTC 2010 i686 GNU/Linux
            Reporter: Chris Wilson


I have a query that generates about 2,000 rows in a summary table. It runs fast enough (~30
seconds) on MySQL. The same query on Derby runs for about 10 minutes and then fails with an
OutOfMemoryError.

I have created a test case to reproduce the problem. It's not minimal because it relies on
a rather large dataset to reproduce it, and it's not trivial, but I don't mind doing a bit
of work trimming it if someone can point me in the necessary direction.

You can check out the test case from our Subversion server here:

  http://rita.wfplogistics.org/svn/trackrita/rita/doc/derby-oom-slow-query

which includes a pre-built Derby database in "testdb.derby". If this database is deleted,
"test.sh" will recreate it, but that takes about 10-15 minutes.

Just modify the script "test.sh" to point to your Derby libraries, and run it (or just execute
the commands in "movement_complete.sql") to demonstrate the problem. You can view the source
of that file online here:

  http://rita.wfplogistics.org/trac/browser/rita/conf/movement_complete.sql

The first "insert into movement_complete" (starting around line 4) takes about 15 seconds
to complete and inserts 5890 rows. The second, starting around line 54, does not complete
in reasonable time on Derby. On MySQL, it runs in 28 seconds and inserts 2038 rows. On Derby,
after 10 minutes I get:

JAVA ERROR: java.lang.OutOfMemoryError: Java heap space
ij> ERROR X0Y67: Cannot issue rollback in a nested connection when there 
is a pending operation in the parent connection.
(process exits)

It does not output the query plan in this case.

Following the suggestion of Bryan Pendleton, I tried increasing the JVM memory limit from
the default to 1024m, and this allows the query to finish executing quite quickly. I guess
that means that the optimiser is just taking a lot of memory to 
optimise the query, and it spends forever in GC before finally hitting OOM and giving up when
using the default settings.

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