org.mapdb

Class BTreeKeySerializer<K>

java.lang.Object

org.mapdb.BTreeKeySerializer<K>

Type Parameters:

K - type of key

Direct Known Subclasses:

BTreeKeySerializer.BasicKeySerializer, BTreeKeySerializer.Tuple2KeySerializer, BTreeKeySerializer.Tuple3KeySerializer, BTreeKeySerializer.Tuple4KeySerializer, BTreeKeySerializer.Tuple5KeySerializer, BTreeKeySerializer.Tuple6KeySerializer

public abstract class BTreeKeySerializer<K>
extends Object

Custom serializer for BTreeMap keys which enables [Delta encoding](https://en.wikipedia.org/wiki/Delta_encoding). Keys in BTree Nodes are sorted, this enables number of tricks to save disk space. For example for numbers we may store only difference between subsequent numbers, for string we can only take suffix, etc...

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	BTreeKeySerializer.BasicKeySerializer Basic Key Serializer which just writes data without applying any compression.
static class	BTreeKeySerializer.Tuple2KeySerializer<A,B> Applies delta compression on array of tuple.
static class	BTreeKeySerializer.Tuple3KeySerializer<A,B,C> Applies delta compression on array of tuple.
static class	BTreeKeySerializer.Tuple4KeySerializer<A,B,C,D> Applies delta compression on array of tuple.
static class	BTreeKeySerializer.Tuple5KeySerializer<A,B,C,D,E> Applies delta compression on array of tuple.
static class	BTreeKeySerializer.Tuple6KeySerializer<A,B,C,D,E,F> Applies delta compression on array of tuple.

Field Summary

Fields

Modifier and Type	Field and Description
static BTreeKeySerializer	BASIC
static BTreeKeySerializer<String>	STRING Applies delta packing on java.lang.String.
static BTreeKeySerializer.Tuple2KeySerializer	TUPLE2 Tuple2 Serializer which uses Default Serializer from DB and expect values to implement Comparable interface.
static BTreeKeySerializer.Tuple3KeySerializer	TUPLE3 Tuple3 Serializer which uses Default Serializer from DB and expect values to implement Comparable interface.
static BTreeKeySerializer.Tuple4KeySerializer	TUPLE4 Tuple4 Serializer which uses Default Serializer from DB and expect values to implement Comparable interface.
static BTreeKeySerializer<Integer>	ZERO_OR_POSITIVE_INT Applies delta packing on java.lang.Integer.
static BTreeKeySerializer<Long>	ZERO_OR_POSITIVE_LONG Applies delta packing on java.lang.Long.

Constructor Summary

Constructors

Constructor and Description
BTreeKeySerializer()

Method Summary

Modifier and Type	Method and Description
abstract Object[]	deserialize(DataInput in, int start, int end, int size) Deserializes keys for single BTree Node.
abstract Comparator<K>	getComparator() Some key serializers may only work with they own comparators.
static byte[]	leadingValuePackRead(DataInput in, byte[] previous, int ignoreLeadingCount) Read previously written data from leadingValuePackWrite() method.
static void	leadingValuePackWrite(DataOutput out, byte[] buf, byte[] previous, int ignoreLeadingCount) This method is used for delta compression for keys.
abstract void	serialize(DataOutput out, int start, int end, Object[] keys) Serialize keys from single BTree Node.

Methods inherited from class java.lang.Object

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

Field Detail

BASIC

public static final BTreeKeySerializer BASIC

ZERO_OR_POSITIVE_LONG

public static final BTreeKeySerializer<Long> ZERO_OR_POSITIVE_LONG

Applies delta packing on java.lang.Long. All keys must be non negative. Difference between consequential numbers is also packed itself, so for small diffs it takes only single byte per number.

ZERO_OR_POSITIVE_INT

public static final BTreeKeySerializer<Integer> ZERO_OR_POSITIVE_INT

Applies delta packing on java.lang.Integer. All keys must be non negative. Difference between consequential numbers is also packed itself, so for small diffs it takes only single byte per number.

STRING

public static final BTreeKeySerializer<String> STRING

Applies delta packing on java.lang.String. This serializer splits consequent strings to two parts: shared prefix and different suffix. Only suffix is than stored.

TUPLE2

public static final BTreeKeySerializer.Tuple2KeySerializer TUPLE2

Tuple2 Serializer which uses Default Serializer from DB and expect values to implement Comparable interface.

TUPLE3

public static final BTreeKeySerializer.Tuple3KeySerializer TUPLE3

Tuple3 Serializer which uses Default Serializer from DB and expect values to implement Comparable interface.

TUPLE4

public static final BTreeKeySerializer.Tuple4KeySerializer TUPLE4

Tuple4 Serializer which uses Default Serializer from DB and expect values to implement Comparable interface.

Constructor Detail

BTreeKeySerializer

public BTreeKeySerializer()

Method Detail

serialize

public abstract void serialize(DataOutput out,
                               int start,
                               int end,
                               Object[] keys)
                        throws IOException

Serialize keys from single BTree Node.

Parameters:

out - output stream where to put ata

start - where data start in array. Before this index all keys are null

end - where data ends in array (exclusive). From this index all keys are null

keys - array of keys for single BTree Node

Throws:

IOException

deserialize

public abstract Object[] deserialize(DataInput in,
                                     int start,
                                     int end,
                                     int size)
                              throws IOException

Deserializes keys for single BTree Node. To

Parameters:

in - input stream to read data from

start - where data start in array. Before this index all keys are null

end - where data ends in array (exclusive). From this index all keys are null

size - size of array which should be returned

Returns:

array of keys for single BTree Node

Throws:

IOException

getComparator

public abstract Comparator<K> getComparator()

Some key serializers may only work with they own comparators. For example delta-packing stores increments between numbers and requires ascending order. So Key Serializer may provide its own comparator.

Returns:

comparator which must be used with this method. `null` if comparator is not strictly required.

leadingValuePackRead

public static byte[] leadingValuePackRead(DataInput in,
                                          byte[] previous,
                                          int ignoreLeadingCount)
                                   throws IOException

Read previously written data from leadingValuePackWrite() method. author: Kevin Day

Throws:

IOException

leadingValuePackWrite

public static void leadingValuePackWrite(DataOutput out,
                                         byte[] buf,
                                         byte[] previous,
                                         int ignoreLeadingCount)
                                  throws IOException

This method is used for delta compression for keys. Writes the contents of buf to the DataOutput out, with special encoding if there are common leading bytes in the previous group stored by this compressor. author: Kevin Day

Throws:

IOException