com.persistit.policy

Class SplitPolicy

java.lang.Object

com.persistit.policy.SplitPolicy

public abstract class SplitPolicy
extends Object

Policies for determining the balance between left and right pages when insertion causes a page to split.

Field Summary

Fields

Modifier and Type	Field and Description
static SplitPolicy	EVEN_BIAS Allocate as records evenly between left and right pages
static SplitPolicy	LEFT_BIAS Allocate as many records as possible to the left page
static SplitPolicy	LEFT90_BIAS Allocate all records to the left page until it is about 90% full, then allocate remaining records to the right page.
static SplitPolicy	NICE_BIAS Allocate about 2/3 of records to the left and 1/3 to the right page
static SplitPolicy	PACK_BIAS Equivalent to LEFT90_BIAS or {RIGHT90_BIAS when records are being inserted in sequential key order, otherwise equivalent to NICE_BIAS
static SplitPolicy	RIGHT_BIAS Allocate as many records as possible to the right page
static SplitPolicy	RIGHT90_BIAS Allocate all records to the right page until it is about 90% full, then allocate remaining records to the right page.

Constructor Summary

Constructors

Constructor and Description
SplitPolicy()

Method Summary

Modifier and Type	Method and Description
static SplitPolicy	forName(String name)
abstract int	splitFit(Buffer buffer, int kbOffset, int insertAt, boolean replace, int leftSize, int rightSize, int currentSize, int virtualSize, int capacity, int splitBest, Exchange.Sequence sequence) Determines the quality of fit for a specified candidate split 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 SplitPolicy LEFT_BIAS

Allocate as many records as possible to the left page

RIGHT_BIAS

public static final SplitPolicy RIGHT_BIAS

Allocate as many records as possible to the right page

EVEN_BIAS

public static final SplitPolicy EVEN_BIAS

Allocate as records evenly between left and right pages

NICE_BIAS

public static final SplitPolicy NICE_BIAS

Allocate about 2/3 of records to the left and 1/3 to the right page

PACK_BIAS

public static final SplitPolicy PACK_BIAS

Equivalent to LEFT90_BIAS or {RIGHT90_BIAS when records are being inserted in sequential key order, otherwise equivalent to NICE_BIAS

LEFT90_BIAS

public static final SplitPolicy LEFT90_BIAS

Allocate all records to the left page until it is about 90% full, then allocate remaining records to the right page. Like LEFT_BIAS except this policy attempts to leave the left page 10% empty.

RIGHT90_BIAS

public static final SplitPolicy RIGHT90_BIAS

Allocate all records to the right page until it is about 90% full, then allocate remaining records to the right page. Like RIGHT_BIAS except this policy attempts to leave the right page 10% empty.

Constructor Detail

SplitPolicy

public SplitPolicy()

Method Detail

forName

public static SplitPolicy forName(String name)

splitFit

public abstract int splitFit(Buffer buffer,
                             int kbOffset,
                             int insertAt,
                             boolean replace,
                             int leftSize,
                             int rightSize,
                             int currentSize,
                             int virtualSize,
                             int capacity,
                             int splitBest,
                             Exchange.Sequence sequence)

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

Parameters:

buffer - the buffer being split.

kbOffset - offset of the proposed keyblock that will become the first key of the right sibling page.

insertAt - offset of the keyblock where the record insertion will occur.

replace - true if the record at kbOffset is being replaced

leftSize - size of the left sibling page that would result if the split were done at this candidate location.

rightSize - size of the right sibling page that would result if the split were done at this candidate location.

currentSize - size of the page prior to insertion.

virtualSize - size of the page that would result where the insertion to occur without splitting the page. (This is usually larger than the actual capacity of the buffer, which is why it needs to be split.)

capacity - Actual available bytes in a page.

splitBest - the previous best-fit result from this method, or 0 if there is no candidate split location yet.

sequence - current sequential insert state

Returns:

measure of goodness of fit.