com.bigdata.btree.raba.codec

Class FixedLengthValueRabaCoder

java.lang.Object

com.bigdata.btree.raba.codec.FixedLengthValueRabaCoder

All Implemented Interfaces:

IRabaCoder, Externalizable, Serializable

public class FixedLengthValueRabaCoder
extends Object
implements IRabaCoder, Externalizable

This class does not offer any compression. It merely stores byte[][] whose individual elements have a fixed length specified in the constructor in a manner suitable for fast random access. This is useful if the values are a fixed length, application specific coding is either not obvious or not desired, and you wish to emphasize speed of data access over compression. This class only supports B+Tree values.

Binary Format

 version : byte
 size    : int32
 nulls   : BytesUtil.bitFlagByteLength(size)
 values  : size * len
 

where

size

The #of elements in the IRaba.

nulls

A vector of bit flags identifying null values. The length of the vector is rounded up to the nearest whole byte based on size.

len

The fixed length of each non-null value as specified to the constructor.

values

The uncompressed representation of each fixed length value. In order to avoid the overhead of an offset map, null values occupy the same space in the array as non-null values.

Author:

Bryan Thompson

See Also:

Serialized Form

Constructor Summary

Constructors

Constructor and Description
FixedLengthValueRabaCoder() De-serialization ctor.
FixedLengthValueRabaCoder(int len) Designated constructor.

Method Summary

Methods

Modifier and Type	Method and Description
ICodedRaba	decode(AbstractFixedByteArrayBuffer data) Return an IRaba which can access the coded data.
AbstractFixedByteArrayBuffer	encode(IRaba raba, DataOutputBuffer buf) Encode the data.
ICodedRaba	encodeLive(IRaba raba, DataOutputBuffer buf) Encode the data, returning an ICodedRaba.
int	getLength() The required length for all non-null values.
boolean	isDuplicateKeys() Return true iff this IRabaCoder supports duplicate keys.
boolean	isKeyCoder() No.
boolean	isValueCoder() Yes.
void	readExternal(ObjectInput in)
void	writeExternal(ObjectOutput out)

Methods inherited from class java.lang.Object

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

Constructor Detail

FixedLengthValueRabaCoder

public FixedLengthValueRabaCoder()

De-serialization ctor.

FixedLengthValueRabaCoder

public FixedLengthValueRabaCoder(int len)

Designated constructor.

Parameters:

len - The length of the byte[] value for each non-null tuple. IRabas having values with a different length will result in a runtime exception when they are encoded.

Method Detail

isKeyCoder

public final boolean isKeyCoder()

No.

Specified by:

isKeyCoder in interface IRabaCoder

isValueCoder

public final boolean isValueCoder()

Yes.

Specified by:

isValueCoder in interface IRabaCoder

isDuplicateKeys

public boolean isDuplicateKeys()

Description copied from interface: IRabaCoder

Return true iff this IRabaCoder supports duplicate keys.

Specified by:

isDuplicateKeys in interface IRabaCoder

See Also:

Stochastic Results With Analytic Query Mode

getLength

public final int getLength()

The required length for all non-null values.

writeExternal

public void writeExternal(ObjectOutput out)
                   throws IOException

Specified by:

writeExternal in interface Externalizable

Throws:

IOException

readExternal

public void readExternal(ObjectInput in)
                  throws IOException,
                         ClassNotFoundException

Specified by:

readExternal in interface Externalizable

Throws:

IOException

ClassNotFoundException

encodeLive

public ICodedRaba encodeLive(IRaba raba,
                    DataOutputBuffer buf)

Encode the data, returning an ICodedRaba. Implementations of this method should be optimized for the very common use case where the caller requires immediate access to the coded data record. In that case, many of the IRabaCoder implementations can be optimized by passing the underlying decoding object directly into an alternative constructor for the ICodedRaba. The byte[] slice for the coded data record is available from ICodedRaba.data().

This method covers the vast major of the use cases for coding data, which is to code B+Tree keys or values for a node or leaf that has been evicted from the AbstractBTree's write retention queue. The common use case is to wrap a coded record that was read from an IRawStore. The IndexSegmentBuilder is a special case, since the coded record will not be used other than to write it on the disk.

Instances of this class will reject IRaba instances having non- null values whose length is not the length specified to the constructor.

Specified by:

encodeLive in interface IRabaCoder

Throws:

UnsupportedOperationException - if the IRaba has a non-null value with a length other than the length specified to the constructor.

encode

public AbstractFixedByteArrayBuffer encode(IRaba raba,
                                  DataOutputBuffer buf)

Description copied from interface: IRabaCoder

Encode the data.

Note: Implementations of this method are typically heavy. While it is always valid to IRabaCoder.encode(IRaba, DataOutputBuffer) an IRaba , DO NOT invoke this arbitrarily on data which may already be coded. The ICodedRaba interface will always be implemented for coded data.

Specified by:

encode in interface IRabaCoder

Parameters:

raba - The data.

buf - A buffer on which the coded data will be written.

Returns:

A slice onto the post-condition state of the caller's buffer whose view corresponds to the coded record. This may be written directly onto an output stream or the slice may be converted to an exact fit byte[].

decode

public ICodedRaba decode(AbstractFixedByteArrayBuffer data)

Description copied from interface: IRabaCoder

Return an IRaba which can access the coded data. In general, implementations SHOULD NOT materialize a backing byte[][]. Instead, the implementation should access the data in place within the caller's buffer. Frequently used fields MAY be cached, but the whole point of the IRabaCoder is to minimize the in-memory footprint for the B+Tree by using a coded (aka compressed) representation of the keys and values whenever possible.

Specified by:

decode in interface IRabaCoder

Parameters:

data - The record containing the coded data.

Returns:

A view of the coded data.