Dag, et al. if I may add a bit of color to what's happening...
I've done lots of various tests (unfortunately, still unable to distill it down
to an easy-to-reproduce tester).
And what I discovered is baffling...
The issue seems to occur (with 100% certainty) under the following
circumstances:
(1) two db connections - one to Derby (in-memory only mode) and Oracle
(2) a prepared statement is executed (such as "select * from <table>") against
Derby
(3) Oracle is queried for tables with:
final ResultSet resultSet = databaseMetaData.getTables(null, null, null, new
String[]{"TABLE"});
(4) if the result set from (2) is iterated over AFTER the (3) then Derby fails
with the described NPE; however, if it is iterated over BEFORE (3), then OK!
It may also be worth noting that my resultsets are made "rewindable", i.e. with:
statement = connection.prepareStatement(
sql,
ResultSet.TYPE_SCROLL_INSENSITIVE,
ResultSet.CONCUR_READ_ONLY);
Finally: although I am completely perplexed as to what's causing this problem,
I found a work-around which, in my estimation, will have minimal impact: at a
particular point in my code (but effectively before calling getTables() in
(3)), the result set from (2) is iterated to the first record and then rewound:
(not exact code, but that's what effectively is occurring):
If (resultSet.next()) {
resultSet.beforeFirst();
}
As odd as it sounds, it seems to have fixed the issue...
I am planning to return to this as time allows. Then I may be able to create a
stand-alone tester.
But if you have any thoughts as to what might be going on, I would be most
appreciative.
Regards,
Pavel.
-----Original Message-----
From: Dag Wanvik [mailto:dag.wan...@oracle.com]
Sent: Monday, December 10, 2012 3:15 PM
To: derby-user@db.apache.org
Subject: Re: NPE
On 10.12.2012 19:21, Pavel Bortnovskiy wrote:
> I upgraded to 10.9.1.0 and rerun with debug libraries (please disregard my
> previous message).
>
> Mon Dec 10 13:19:44 EST 2012
> Thread[DatabasePublisher[BOND_WRITER],5,main] (XID = 289), (SESSIONID = 5),
> (DATABASE = memory:test), (DRDAID = null), Failed Statement is: select *
> from READER java.lang.NullPointerException
> at
> org.apache.derby.impl.store.access.conglomerate.GenericScanController.reopenAfterEndTransaction(GenericScanController.java:1048)
> at
It looks like "container" is null, cf. the line 1048:
case SCAN_HOLD_INIT:
***> reusableRecordIdSequenceNumber =
container.getReusableRecordIdSequenceNumber();
i.e. has been closed, cf the assignment just above:
ContainerHandle container = open_conglom.reopen();
The call to reopen just returns null if OpenConglomerate has been closed
somehow.
Smells like a race condition of sorts, maybe some missing synchronization in
the Derby code.
If you are able to post a self contained repro program, although this might be
tricky if this is indeed a race, this would increase your chances of having
this fixed soon..
Thanks,
Dag
In any case the NullPointerException shoudln't be seen by the application
code, so this is a bug.
> org.apache.derby.impl.store.access.conglomerate.GenericScanController.fetchRows(GenericScanController.java:622)
> at
> org.apache.derby.impl.store.access.heap.HeapScan.fetchNextGroup(HeapScan.java:322)
> at
> org.apache.derby.impl.sql.execute.BulkTableScanResultSet.reloadArray(BulkTableScanResultSet.java:353)
> at
> org.apache.derby.impl.sql.execute.BulkTableScanResultSet.getNextRowCore(BulkTableScanResultSet.java:308)
> at
> org.apache.derby.impl.sql.execute.ProjectRestrictResultSet.getNextRowCore(ProjectRestrictResultSet.java:261)
> at
> org.apache.derby.impl.sql.execute.ScrollInsensitiveResultSet.getNextRowFromSource(ScrollInsensitiveResultSet.java:801)
> at
> org.apache.derby.impl.sql.execute.ScrollInsensitiveResultSet.getNextRowCore(ScrollInsensitiveResultSet.java:518)
> at
> org.apache.derby.impl.sql.execute.BasicNoPutResultSetImpl.getNextRow(BasicNoPutResultSetImpl.java:478)
> at
> org.apache.derby.impl.jdbc.EmbedResultSet.movePosition(EmbedResultSet.java:432)
> at
> org.apache.derby.impl.jdbc.EmbedResultSet.next(EmbedResultSet.java:376)
> at QueryResults$1.hasNext(QueryResults.java:268)
> at DatabasePublisher.process(DatabasePublisher.java:318)
> at java.lang.Thread.run(Thread.java:662)
>
> -----Original Message-----
> From: Rick Hillegas [mailto:rick.hille...@oracle.com]
> Sent: Monday, December 10, 2012 1:05 PM
> To: derby-user@db.apache.org
> Subject: Re: NPE
>
> Hi Pavel,
>
> Can you reproduce this problem with the debug version of Derby? That would
> give us line numbers in the stack trace.
>
> Thanks,
> -Rick
>
> On 12/10/12 9:23 AM, Pavel Bortnovskiy wrote:
>> Hello:
>>
>> While testing my application, which uses Derby in memory-only mode, I
>> get NPE inside Derby under "mysterious" circumstances.
>>
>> At this point, I can't even figure out what's triggering it and where
>> this could happen, but let me preempt my troubleshooting with some
>> stack traces. Perhaps someone, with good knowledge of Derby's code,
>> may offer some explanation. Here are some stack traces:
>>
>> Mon Dec 10 12:12:36 EST 2012 Thread[DatabasePublisher[WRITER],5,main]
>> (XID = 235), (SESSIONID = 5), (DATABASE = memory:test), (DRDAID =
>> null), Failed Statement is: select * from READER
>>
>> java.lang.NullPointerException
>>
>> at
>> org.apache.derby.impl.store.access.conglomerate.GenericScanController.
>> reopenAfterEndTransaction(Unknown
>> Source)
>>
>> at
>> org.apache.derby.impl.store.access.conglomerate.GenericScanController.
>> fetchRows(Unknown
>> Source)
>>
>> at
>> org.apache.derby.impl.store.access.heap.HeapScan.fetchNextGroup(Unkno
>> w
>> n Source)
>>
>> at
>> org.apache.derby.impl.sql.execute.BulkTableScanResultSet.reloadArray(
>> U
>> nknown
>> Source)
>>
>> at
>> org.apache.derby.impl.sql.execute.BulkTableScanResultSet.getNextRowCo
>> r
>> e(Unknown
>> Source)
>>
>> at
>> org.apache.derby.impl.sql.execute.ProjectRestrictResultSet.getNextRow
>> C
>> ore(Unknown
>> Source)
>>
>> at
>> org.apache.derby.impl.sql.execute.ScrollInsensitiveResultSet.getNextR
>> o
>> wFromSource(Unknown
>> Source)
>>
>> at
>> org.apache.derby.impl.sql.execute.ScrollInsensitiveResultSet.getNextR
>> o
>> wCore(Unknown
>> Source)
>>
>> at
>> org.apache.derby.impl.sql.execute.BasicNoPutResultSetImpl.getNextRow(
>> U
>> nknown
>> Source)
>>
>> at org.apache.derby.impl.jdbc.EmbedResultSet.movePosition(Unknown
>> Source)
>>
>> at org.apache.derby.impl.jdbc.EmbedResultSet.next(Unknown Source)
>>
>> at QueryResults$1.hasNext(QueryResults.java:268)
>>
>> at DatabasePublisher.process(DatabasePublisher.java:318)
>>
>> at java.lang.Thread.run(Thread.java:662)
>>
>> or
>>
>> 2012-12-10 12:12:36,537 [DatabasePublisher[WRITER]] ERROR
>> QueryResults
>> - Unable to execute ResultSet.next() for Statement ""select * from
>> READER" [DERBY]"
>>
>> java.sql.SQLException: Java exception: ': java.lang.NullPointerException'.
>>
>> at
>> org.apache.derby.impl.jdbc.SQLExceptionFactory40.getSQLException(Unkn
>> o
>> wn
>> Source)
>>
>> at org.apache.derby.impl.jdbc.Util.newEmbedSQLException(Unknown
>> Source)
>>
>> at org.apache.derby.impl.jdbc.Util.javaException(Unknown Source)
>>
>> at
>> org.apache.derby.impl.jdbc.TransactionResourceImpl.wrapInSQLException
>> (
>> Unknown
>> Source)
>>
>> at
>> org.apache.derby.impl.jdbc.TransactionResourceImpl.handleException(Un
>> k
>> nown
>> Source)
>>
>> at org.apache.derby.impl.jdbc.EmbedConnection.handleException(Unknown
>> Source)
>>
>> at org.apache.derby.impl.jdbc.ConnectionChild.handleException(Unknown
>> Source)
>>
>> at
>> org.apache.derby.impl.jdbc.EmbedResultSet.closeOnTransactionError(Unk
>> n
>> own
>> Source)
>>
>> at org.apache.derby.impl.jdbc.EmbedResultSet.movePosition(Unknown
>> Source)
>>
>> at org.apache.derby.impl.jdbc.EmbedResultSet.next(Unknown Source)
>>
>> at QueryResults$1.hasNext(QueryResults.java:268)
>>
>> at DatabasePublisher.process(DatabasePublisher.java:318)
>>
>> at java.lang.Thread.run(Thread.java:662)
>>
>> Caused by: java.sql.SQLException: Java exception: ':
>> java.lang.NullPointerException'.
>>
>> at
>> org.apache.derby.impl.jdbc.SQLExceptionFactory.getSQLException(Unknow
>> n
>> Source)
>>
>> at
>> org.apache.derby.impl.jdbc.SQLExceptionFactory40.wrapArgsForTransport
>> A
>> crossDRDA(Unknown
>> Source)
>>
>> ... 14 more
>>
>> Caused by: java.lang.NullPointerException
>>
>> at
>> org.apache.derby.impl.store.access.conglomerate.GenericScanController.
>> reopenAfterEndTransaction(Unknown
>> Source)
>>
>> at
>> org.apache.derby.impl.store.access.conglomerate.GenericScanController.
>> fetchRows(Unknown
>> Source)
>>
>> at
>> org.apache.derby.impl.store.access.heap.HeapScan.fetchNextGroup(Unkno
>> w
>> n Source)
>>
>> at
>> org.apache.derby.impl.sql.execute.BulkTableScanResultSet.reloadArray(
>> U
>> nknown
>> Source)
>>
>> at
>> org.apache.derby.impl.sql.execute.BulkTableScanResultSet.getNextRowCo
>> r
>> e(Unknown
>> Source)
>>
>> at
>> org.apache.derby.impl.sql.execute.ProjectRestrictResultSet.getNextRow
>> C
>> ore(Unknown
>> Source)
>>
>> at
>> org.apache.derby.impl.sql.execute.ScrollInsensitiveResultSet.getNextR
>> o
>> wFromSource(Unknown
>> Source)
>>
>> at
>> org.apache.derby.impl.sql.execute.ScrollInsensitiveResultSet.getNextR
>> o
>> wCore(Unknown
>> Source)
>>
>> at
>> org.apache.derby.impl.sql.execute.BasicNoPutResultSetImpl.getNextRow(
>> U
>> nknown
>> Source)
>>
>> ... 6 more
>>
>> One more thing I can share is that this seems to also be a timing
>> problem - if the code is executed slowly, line-by-line in the
>> debugger, then this problem doesn't occur. But if run at full speed,
>> then these exceptions are thrown. The problem is not intermittent and
>> easily reproduced 100% of the time on my end.
>>
>> Any thoughts would be greatly appreciated.
>>
>> Pavel.
>>
>>
>>
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