David Sitsky created DERBY-6975:
-----------------------------------
Summary: Bug in SequenceUpdater.getCurrentValueAndAdvance - break
used instead of continue
Key: DERBY-6975
URL: https://issues.apache.org/jira/browse/DERBY-6975
Project: Derby
Issue Type: Bug
Components: SQL
Affects Versions: 10.14.1.0
Reporter: David Sitsky
I have an application that sporadically gets this exception when inserting a
lot of rows using a sequence generator.
{noformat}
Caused by: ERROR 40XL1: A lock could not be obtained within the time requested
at
org.apache.derby.iapi.error.StandardException.newException(StandardException.java)
at
org.apache.derby.iapi.error.StandardException.newException(StandardException.java)
at
org.apache.derby.impl.sql.catalog.SequenceUpdater.tooMuchContentionException(SequenceUpdater.java)
at
org.apache.derby.impl.sql.catalog.SequenceUpdater.getCurrentValueAndAdvance(SequenceUpdater.java)
at
org.apache.derby.impl.sql.catalog.DataDictionaryImpl.getCurrentValueAndAdvance(DataDictionaryImpl.java)
at
org.apache.derby.impl.sql.execute.BaseActivation.getCurrentValueAndAdvance(BaseActivation.java)
at
org.apache.derby.impl.sql.execute.InsertResultSet.getSetAutoincrementValue(InsertResultSet.java)
at
org.apache.derby.impl.sql.execute.BaseActivation.getSetAutoincrementValue(BaseActivation.java)
at
org.apache.derby.exe.ac560740aax015fx6bc1x68cax000002339e626a.e0(ac560740aax015fx6bc1x68cax000002339e626a.java)
at
org.apache.derby.impl.services.reflect.DirectCall.invoke(DirectCall.java)
at
org.apache.derby.impl.sql.execute.RowResultSet.getNextRowCore(RowResultSet.java)
at
org.apache.derby.impl.sql.execute.NormalizeResultSet.getNextRowCore(NormalizeResultSet.java)
at
org.apache.derby.impl.sql.execute.DMLWriteResultSet.getNextRowCore(DMLWriteResultSet.java)
at
org.apache.derby.impl.sql.execute.InsertResultSet.getNextRowCore(InsertResultSet.java)
at
org.apache.derby.impl.sql.execute.InsertResultSet.open(InsertResultSet.java)
at
org.apache.derby.impl.sql.GenericPreparedStatement.executeStmt(GenericPreparedStatement.java)
at
org.apache.derby.impl.sql.GenericPreparedStatement.execute(GenericPreparedStatement.java)
... 25 more
{noformat}
When I look at the code in question, it comes down to this method:
{code}
/**
* <p>
* Get the next sequence number managed by this generator and advance the
number. Could raise an
* exception if the legal range is exhausted and wrap-around is not allowed.
* Only one thread at a time is allowed through here. We do not want a race
between the
* two calls to the sequence generator: getCurrentValueAndAdvance() and
allocateNewRange().
* </p>
*
* @param returnValue This value is stuffed with the new sequence number.
*/
public synchronized void getCurrentValueAndAdvance
( NumberDataValue returnValue ) throws StandardException
{
//
// We may have to try to get a value from the Sequence Generator twice.
// The first attempt may fail because we need to pre-allocate a new
chunk
// of values.
//
for ( int i = 0; i < 2; i++ )
{
//
// We try to get a sequence number. The SequenceGenerator method is
synchronized
// so only one writer should be in there at a time. Lock contention
is possible if
// someone has selected from SYSSEQUENCES contrary to our advice.
In that case,
// we raise a TOO MUCH CONTENTION exception.
//
long[] cvaa = _sequenceGenerator.getCurrentValueAndAdvance();
int status = (int) cvaa[ SequenceGenerator.CVAA_STATUS ];
long currentValue = cvaa[ SequenceGenerator.CVAA_CURRENT_VALUE ];
long lastAllocatedValue = cvaa[
SequenceGenerator.CVAA_LAST_ALLOCATED_VALUE ];
long numberOfValuesAllocated = cvaa[
SequenceGenerator.CVAA_NUMBER_OF_VALUES_ALLOCATED ];
switch ( status )
{
case SequenceGenerator.RET_OK:
returnValue.setValue( currentValue );
return;
case SequenceGenerator.RET_MARK_EXHAUSTED:
updateCurrentValueOnDisk( currentValue, null );
returnValue.setValue( currentValue );
return;
case SequenceGenerator.RET_ALLOCATE_NEW_VALUES:
if ( updateCurrentValueOnDisk( currentValue, lastAllocatedValue
) )
{
_sequenceGenerator.allocateNewRange( currentValue,
numberOfValuesAllocated );
}
break;
default:
throw unimplementedFeature();
}
}
//
// If we get here, then we failed to allocate a new sequence number
range.
//
throw tooMuchContentionException();
}
{code}
If I understand the intent of this code, in the
SequenceGenerator.RET_ALLOCATE_NEW_VALUES case, we allocate a new sequence
generator range and then we are meant to re-execute the loop again to use it,
however since "break" is used we break out of the for loop and throw the
exception.
It seems if we replace "break" with 'continue" this will work as expected?
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