Package org.apache.jackrabbit.oak.segment

Class Segment

java.lang.Object

org.apache.jackrabbit.oak.segment.Segment

public class Segment
extends Object

A list of records.

Record data is not kept in memory, but some entries are cached (templates, all strings in the segment).

This class includes method to read records from the raw bytes.

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static interface	Segment.RecordConsumer	A consumer of record data.

Field Summary

Fields

Modifier and Type	Field	Description
static int	MAX_SEGMENT_SIZE	Maximum segment size (in bytes)
static int	MEDIUM_LIMIT	The size limit for medium values.

Constructor Summary

Constructors

Constructor	Description
Segment(@NotNull SegmentIdProvider idProvider, @NotNull SegmentId id, @NotNull Buffer data)
Segment(@NotNull SegmentId id, @NotNull SegmentData data, @NotNull RecordNumbers recordNumbers, @NotNull SegmentReferences segmentReferences)

Method Summary

Modifier and Type	Method	Description
void	forEachRecord(Segment.RecordConsumer consumer)	Iterate over the records contained in this segment.
int	getAddress(int offset)	Convert an offset into an address.
@NotNull GCGeneration	getGcGeneration()	Determine the gc generation of this segment.
static GCGeneration	getGcGeneration(SegmentData data, UUID segmentId)	Determine the gc generation a segment from its data.
UUID	getReferencedSegmentId(int index)
int	getReferencedSegmentIdCount()
SegmentId	getSegmentId()
@Nullable String	getSegmentInfo()	Returns the segment meta data of this segment or null if none is present.
SegmentVersion	getSegmentVersion()
byte	readByte(int recordNumber)
byte	readByte(int recordNumber, int offset)
void	readBytes(int recordNumber, int position, byte[] buffer, int offset, int length)
Buffer	readBytes(int recordNumber, int position, int length)
int	size()
String	toString()
void	writeTo(OutputStream stream)

Methods inherited from class java.lang.Object

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

Field Detail

MAX_SEGMENT_SIZE

public static final int MAX_SEGMENT_SIZE

Maximum segment size (in bytes)

See Also:

Constant Field Values

MEDIUM_LIMIT

public static final int MEDIUM_LIMIT

The size limit for medium values. The variable length of medium values is encoded as two bytes with the highest bits of the first byte set to one and zero, which gives us 14 bits for encoding the length of the value. And since small values are never stored as medium ones, we can extend the size range to cover that many longer values.

See Also:

Constant Field Values

Constructor Detail

Segment

public Segment(@NotNull
               @NotNull SegmentIdProvider idProvider,
               @NotNull
               @NotNull SegmentId id,
               @NotNull
               @NotNull Buffer data)

Segment

public Segment(@NotNull
               @NotNull SegmentId id,
               @NotNull
               @NotNull SegmentData data,
               @NotNull
               @NotNull RecordNumbers recordNumbers,
               @NotNull
               @NotNull SegmentReferences segmentReferences)

Method Detail

getSegmentVersion

public SegmentVersion getSegmentVersion()

getSegmentId

public SegmentId getSegmentId()

getReferencedSegmentIdCount

public int getReferencedSegmentIdCount()

getReferencedSegmentId

public UUID getReferencedSegmentId(int index)

getGcGeneration

public static GCGeneration getGcGeneration(SegmentData data,
                                           UUID segmentId)

Determine the gc generation a segment from its data. Note that bulk segments don't have generations (i.e. stay at 0).

Parameters:

data - the data of the segment

segmentId - the id of the segment

Returns:

the gc generation of this segment or GCGeneration.NULL if this is bulk segment.

getGcGeneration

@NotNull
public @NotNull GCGeneration getGcGeneration()

Determine the gc generation of this segment. Note that bulk segments don't have generations (i.e. stay at 0).

Returns:

the gc generation of this segment or 0 if this is bulk segment.

getSegmentInfo

@Nullable
public @Nullable String getSegmentInfo()

Returns the segment meta data of this segment or null if none is present.

The segment meta data is a string of the format "{wid=W,sno=S,gc=G,t=T}" where:

• W is the writer id wid,
• S is a unique, increasing sequence number corresponding to the allocation order of the segments in this store,
• G is the garbage collection generation (i.e. the number of compaction cycles that have been run),
• T is a time stamp according to System.currentTimeMillis().

Returns:

the segment meta data

size

public int size()

readByte

public byte readByte(int recordNumber)

readByte

public byte readByte(int recordNumber,
                     int offset)

readBytes

public void readBytes(int recordNumber,
                      int position,
                      byte[] buffer,
                      int offset,
                      int length)

readBytes

public Buffer readBytes(int recordNumber,
                        int position,
                        int length)

toString

public String toString()

Overrides:

toString in class Object

writeTo

public void writeTo(OutputStream stream)
             throws IOException

Throws:

IOException

getAddress

public int getAddress(int offset)

Convert an offset into an address.

Parameters:

offset -

Returns:

the address corresponding the offset

forEachRecord

public void forEachRecord(Segment.RecordConsumer consumer)

Iterate over the records contained in this segment.

Parameters:

consumer - an instance of Segment.RecordConsumer.