com.persistit.policy

Class JoinPolicy

java.lang.Object

com.persistit.policy.JoinPolicy

public class JoinPolicy
extends Object

Policies for determining the balance between left and right pages when rebalancing page content due to deletion.

Version:

1.0

Field Summary

Fields

Modifier and Type	Field and Description
static JoinPolicy	EVEN_BIAS Balance the allocation of spaces evenly between left and right pages.
static JoinPolicy	LEFT_BIAS Maximize the number of records in the left page, and minimize the number of records in the right page.
static JoinPolicy	RIGHT_BIAS Minimize the number of records in the left page, and maximize the number of records in the right page.

Constructor Summary

Constructors

Modifier	Constructor and Description
protected	JoinPolicy(int bias, String name)

Method Summary

Modifier and Type	Method and Description
boolean	acceptJoin(Buffer buffer, int virtualSize) Determines whether two pages will be permitted to be rejoined during a delete operation.
static JoinPolicy	forName(String name)
String	getName()
int	rebalanceFit(Buffer leftBuffer, Buffer rightBuffer, int kbOffset, int foundAt1, int foundAt2, int virtualSize, int leftSize, int rightSize, int capacity) Determines the quality of fit for a specified candidate join location within a page.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

LEFT_BIAS

public static final JoinPolicy LEFT_BIAS

Maximize the number of records in the left page, and minimize the number of records in the right page.

RIGHT_BIAS

public static final JoinPolicy RIGHT_BIAS

Minimize the number of records in the left page, and maximize the number of records in the right page.

EVEN_BIAS

public static final JoinPolicy EVEN_BIAS

Balance the allocation of spaces evenly between left and right pages.

Constructor Detail

JoinPolicy

protected JoinPolicy(int bias,
                     String name)

Method Detail

forName

public static JoinPolicy forName(String name)

rebalanceFit

public int rebalanceFit(Buffer leftBuffer,
                        Buffer rightBuffer,
                        int kbOffset,
                        int foundAt1,
                        int foundAt2,
                        int virtualSize,
                        int leftSize,
                        int rightSize,
                        int capacity)

Determines the quality of fit for a specified candidate join location within a page. Returns 0 if no join is possible, or a positive integer if a join is possible. The caller will call joinFit to evaluate several possible join locations, and will choose the one yielding the largest value of this method.

Parameters:

leftBuffer - The left Buffer>

rightBuffer - The right Buffer

kbOffset - The key block proposed as the new split point

foundAt1 - First key being deleted from left page

foundAt2 - First key not being deleted from right page

virtualSize - The total size of both pages

leftSize - Size the left page would have if split here

rightSize - Size the right page would have if split here

capacity - The total space available in a page (less overhead)

Returns:

A measure of "goodness of fit" This method should return the largest such measure for the best split point

acceptJoin

public boolean acceptJoin(Buffer buffer,
                          int virtualSize)

Determines whether two pages will be permitted to be rejoined during a delete operation.

Parameters:

buffer -

virtualSize -

Returns:

true if the buffer will accept content of the specified size

getName

public String getName()

Returns:

name of the policy