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https://issues.apache.org/jira/browse/DERBY-3479?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12575373#action_12575373
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Knut Anders Hatlen commented on DERBY-3479:
-------------------------------------------

I noticed that other tests that depend on stable query plans (wisconsin and 
StalePlansTest) set derby.storage.checkpointInterval=100000. I tried to add 
this property to predicatePushdown_derby.properties, and that seemed to 
stabilize the test.

StalePlansTest contains some magic to flush the row count for the tables. I 
don't understand exactly what it does, in particular I don't understand why 
"select count(c1) from flusher" is needed to make the row count for other 
tables than flusher visible. Perhaps changing the concurrency/timing in the 
buffer manager somehow changes when the row count is flushed, and thereby it 
makes the optimizer choose a different plan?

> Changed/unexpected query plan when running test 'lang/predicatePushdown.sql'
> ----------------------------------------------------------------------------
>
>                 Key: DERBY-3479
>                 URL: https://issues.apache.org/jira/browse/DERBY-3479
>             Project: Derby
>          Issue Type: Bug
>          Components: Regression Test Failure
>    Affects Versions: 10.4.0.0
>         Environment: OS: Solaris 10 6/06 s10x_u2wos_09a X86 64bits - SunOS 
> 5.10 Generic_118855-14
> JVM: Sun Microsystems Inc., java version "1.6.0_04", Java(TM) SE Runtime 
> Environment (build 1.6.0_04-b12), Java HotSpot(TM) Client VM (build 10.0-b19, 
> mixed mode)
>            Reporter: Ole Solberg
>
> Seen in tinderbox since r631930.
> See e.g. 
> http://dbtg.thresher.com/derby/test/tinderbox_trunk16/jvm1.6/testing/testlog/SunOS-5.10_i86pc-i386/631932-derbyall_diff.txt
>  :
> *** Start: predicatePushdown jdk1.6.0_04 derbyall:derbylang 2008-02-28 
> 14:02:49 ***
> 9285 del
> <             Rows seen from the left = 20
> 9285a9285
> >             Rows seen from the left = 10
> 9297 del
> <                     Rows seen from the right = 20
> 9297a9297
> >                     Rows seen from the right = 10
> 9299 del
> <                     Rows returned = 20
> 9299a9299
> >                     Rows returned = 10
> .
> .
> .

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