java/engine/org/apache/derby/impl/sql/catalog/SequenceRange.java

/*

   Derby - Class org.apache.derby.impl.sql.catalog.SequenceRange

   Licensed to the Apache Software Foundation (ASF) under one or more
   contributor license agreements.  See the NOTICE file distributed with
   this work for additional information regarding copyright ownership.
   The ASF licenses this file to you under the Apache License, Version 2.0
   (the "License"); you may not use this file except in compliance with
   the License.  You may obtain a copy of the License at

      http://www.apache.org/licenses/LICENSE-2.0

   Unless required by applicable law or agreed to in writing, software
   distributed under the License is distributed on an "AS IS" BASIS,
   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   See the License for the specific language governing permissions and
   limitations under the License.

 */

package org.apache.derby.impl.sql.catalog;

import org.apache.derby.catalog.SequencePreallocator;

/**
 * <p>
 * Default Derby logic for determining how many values to pre-allocate for an
 * identity column or sequence.
 * </p>
 */
public  class   SequenceRange   implements  SequencePreallocator
{
    ///////////////////////////////////////////////////////////////////////////////////
    //
    // CONSTANTS
    //
    ///////////////////////////////////////////////////////////////////////////////////

    /**
     * Default number of values to pre-allocate. Other databases use a preallocation size
     * of 20 (see DERBY-4437). We boosted this to 100 in order to get better concurrency,
     * after fixing correctness problems in pre-allocation (see DERBY-5493).
     */
    private static final int DEFAULT_PREALLOCATION_COUNT = 100;

    ///////////////////////////////////////////////////////////////////////////////////
    //
    // STATE
    //
    ///////////////////////////////////////////////////////////////////////////////////

    private int _rangeSize;

    ///////////////////////////////////////////////////////////////////////////////////
    //
    // CONSTRUCTOR
    //
    ///////////////////////////////////////////////////////////////////////////////////

    /** <p>0-arg constructore needed to satisfy the SequencePreallocator contract.</p> */
    public  SequenceRange()
    {
        this( DEFAULT_PREALLOCATION_COUNT );
    }

    public  SequenceRange( int rangeSize )
    {
        if ( rangeSize <= 0 ) { rangeSize = DEFAULT_PREALLOCATION_COUNT; }
        
        _rangeSize = rangeSize;
    }

    ///////////////////////////////////////////////////////////////////////////////////
    //
    // SequencePreallocator BEHAVIOR
    //
    ///////////////////////////////////////////////////////////////////////////////////

    public  int nextRangeSize
        (
         String schemaName,
         String sequenceName
         )
    {
        return _rangeSize;
    }


}