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https://issues.apache.org/jira/browse/DERBY-5124?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13005629#comment-13005629
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Knut Anders Hatlen commented on DERBY-5124:
-------------------------------------------
The NPE happens in the logging:
// Log some information.
log(asBackgroundTask, td,
"wrote stats for index " +
dd.getConglomerateDescriptor(index).getDescriptorName() +
" (" + index + "): rows=" + numRows +
", card=" + cardToStr(cardinality));
Presumably dd.getConglomerateDescriptor() returns null because the index
doesn't exist anymore.
> NPE or assert failure printed when dropping table while statistics are
> written out
> ----------------------------------------------------------------------------------
>
> Key: DERBY-5124
> URL: https://issues.apache.org/jira/browse/DERBY-5124
> Project: Derby
> Issue Type: Bug
> Components: Services
> Affects Versions: 10.8.0.0
> Reporter: Knut Anders Hatlen
>
> To find out what would happen if a table was dropped while its statistics
> were being written to disk, I put a breakpoint in
> IndexStatisticsImpl.writeUpdatedStats() right after the call to
> dropStatisticsDescriptors(), started an ij session in the debugger and
> executed some statements to make the istat code kick in. When the breakpoint
> was hit, I dropped the table being updated in ij, before letting the istat
> thread continue.
> With insane jars, the following NPE was printed on the ij console:
> Exception in thread "index-stat-thread" java.lang.NullPointerException
> at
> org.apache.derby.impl.services.daemon.IndexStatisticsDaemonImpl.writeUpdatedStats(IndexStatisticsDaemonImpl.java:556)
> at
> org.apache.derby.impl.services.daemon.IndexStatisticsDaemonImpl.updateIndexStatsMinion(IndexStatisticsDaemonImpl.java:486)
> at
> org.apache.derby.impl.services.daemon.IndexStatisticsDaemonImpl.generateStatistics(IndexStatisticsDaemonImpl.java:323)
> at
> org.apache.derby.impl.services.daemon.IndexStatisticsDaemonImpl.processingLoop(IndexStatisticsDaemonImpl.java:759)
> at
> org.apache.derby.impl.services.daemon.IndexStatisticsDaemonImpl.run(IndexStatisticsDaemonImpl.java:675)
> at java.lang.Thread.run(Thread.java:662)
> Apart from the stack trace being printed, nothing bad happened. The istat
> thread was able to recover, and the ij session was unaffected too.
> Using a debug build, I got an assert failure instead:
> Exception in thread "index-stat-thread"
> org.apache.derby.shared.common.sanity.AssertFailure: ASSERT FAILED
> transaction not pristine
> at
> org.apache.derby.shared.common.sanity.SanityManager.THROWASSERT(SanityManager.java:162)
> at
> org.apache.derby.shared.common.sanity.SanityManager.THROWASSERT(SanityManager.java:147)
> at
> org.apache.derby.impl.services.daemon.IndexStatisticsDaemonImpl.processingLoop(IndexStatisticsDaemonImpl.java:810)
> at
> org.apache.derby.impl.services.daemon.IndexStatisticsDaemonImpl.run(IndexStatisticsDaemonImpl.java:675)
> at java.lang.Thread.run(Thread.java:662)
> The assert failure prevented some cleanup from happening, so the istat thread
> seemed to hold on to a lock on SYSSTATISTICS, so the following statement
> would keep failing in ij after on:
> ij> select * from sys.sysstatistics;
> STATID |REFERENCEID
> |TABLEID |CREATIONTIMESTAMP
> |&|VALID|COLCOUNT |STATISTICS
> --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
> ERROR 40XL1: A lock could not be obtained within the time requested
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