Package org.hibernate.id.enhanced

Class HiLoOptimizer

  • All Implemented Interfaces:
    Optimizer
    public class HiLoOptimizer
extends AbstractOptimizer
    Optimizer which applies a 'hilo' algorithm in memory to achieve optimization.

    A 'hilo' algorithm is simply a means for a single value stored in the database to represent a "bucket" of possible, contiguous values. The database value identifies which particular bucket we are on.

    This database value must be paired with another value that defines the size of the bucket; the number of possible values available. The incrementSize serves this purpose. The naming here is meant more for consistency in that this value serves the same purpose as the increment supplied to the PooledOptimizer.

    The general algorithms used to determine the bucket are:

    1. upperLimit = (databaseValue * incrementSize) + 1
    2. lowerLimit = upperLimit - incrementSize
    As an example, consider a case with incrementSize of 20. Initially the database holds 1:
    1. upperLimit = (1 * 20) + 1 = 21
    2. lowerLimit = 21 - 20 = 1
    From there we increment the value from lowerLimit until we reach the upperLimit, at which point we would define a new bucket. The database now contains 2, though incrementSize remains unchanged:
    1. upperLimit = (2 * 20) + 1 = 41
    2. lowerLimit = 41 - 20 = 21
    And so on...

    Note, 'value' always (after init) holds the next value to return

    • Constructor Detail

      • HiLoOptimizer

        public HiLoOptimizer​(java.lang.Class returnClass,
                     int incrementSize)
        Constructs a HiLoOptimizer
        Parameters:
        returnClass - The Java type of the values to be generated
        incrementSize - The increment size.

    • Method Detail

      • generate

        public java.io.Serializable generate​(AccessCallback callback)
        Description copied from interface: Optimizer
        Generate an identifier value accounting for this specific optimization. All known implementors are synchronized. Consider carefully if a new implementation could drop this requirement.
        Parameters:
        callback - Callback to access the underlying value source.
        Returns:
        The generated identifier value.

      • getLastSourceValue

        public IntegralDataTypeHolder getLastSourceValue()
        Description copied from interface: Optimizer
        A common means to access the last value obtained from the underlying source. This is intended for testing purposes, since accessing the underlying database source directly is much more difficult.
        Returns:
        The last value we obtained from the underlying source; null indicates we have not yet consulted with the source.

      • applyIncrementSizeToSourceValues

        public boolean applyIncrementSizeToSourceValues()
        Description copied from interface: Optimizer
        Are increments to be applied to the values stored in the underlying value source?
        Returns:
        True if the values in the source are to be incremented according to the defined increment size; false otherwise, in which case the increment is totally an in memory construct.

      • getLastValue

        public IntegralDataTypeHolder getLastValue()
        Getter for property 'lastValue'.

        Exposure intended for testing purposes.

        Returns:
        Value for property 'lastValue'.

      • getHiValue

        public IntegralDataTypeHolder getHiValue()
        Getter for property 'upperLimit'.

        Exposure intended for testing purposes.

        Returns:
        Value for property 'upperLimit'.