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From "David Sitsky (JIRA)" <j...@apache.org>
Subject [jira] [Created] (DERBY-6975) Bug in SequenceUpdater.getCurrentValueAndAdvance - break used instead of continue
Date Tue, 31 Oct 2017 01:18:00 GMT
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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