org.apache.jackrabbit.oak.plugins.segment

Class Segment

java.lang.Object

org.apache.jackrabbit.oak.plugins.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.

Field Summary

Fields

Modifier and Type	Field and Description
static int	BLOB_ID_SMALL_LIMIT Maximum size of small blob IDs.
static int	MAX_SEGMENT_SIZE Maximum segment size.
static int	MEDIUM_LIMIT The size limit for medium values.
static int	RECORD_ALIGN_BITS The number of bytes (or bits of address space) to use for the alignment boundary of segment records.
static int	REF_COUNT_OFFSET

Constructor Summary

Constructors

Constructor and Description
Segment(SegmentTracker tracker, SegmentId id, ByteBuffer data)
Segment(SegmentTracker tracker, SegmentId id, ByteBuffer data, SegmentVersion version)

Method Summary

Methods

Modifier and Type	Method and Description
static int	align(int address, int boundary) Align an address on the given boundary
static int	decode(short offset) Decode a 4 byte aligned segment offset.
static short	encode(int offset) Encode a segment offset into a 4 byte aligned address packed into a short.
long	getCacheSize()
List<SegmentId>	getReferencedIds()
int	getRootCount()
int	getRootOffset(int index)
RecordType	getRootType(int index)
SegmentId	getSegmentId()
String	getSegmentInfo() Returns the segment meta data of this segment or null if none is present.
int	size()
String	toString()
void	writeTo(OutputStream stream) Writes this segment to the given output stream.

Methods inherited from class java.lang.Object

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

Field Detail

RECORD_ALIGN_BITS

public static final int RECORD_ALIGN_BITS

The number of bytes (or bits of address space) to use for the alignment boundary of segment records.

See Also:

Constant Field Values

MAX_SEGMENT_SIZE

public static final int MAX_SEGMENT_SIZE

Maximum segment size. Record identifiers are stored as three-byte sequences with the first byte indicating the segment and the next two the offset within that segment. Since all records are aligned at four-byte boundaries, the two bytes can address up to 256kB of record data.

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

BLOB_ID_SMALL_LIMIT

public static final int BLOB_ID_SMALL_LIMIT

Maximum size of small blob IDs. A small blob ID is stored in a value record whose length field contains the pattern "1110" in its most significant bits. Since two bytes are used to store both the bit pattern and the actual length of the blob ID, a maximum of 2^12 values can be stored in the length field.

See Also:

Constant Field Values

REF_COUNT_OFFSET

public static final int REF_COUNT_OFFSET

See Also:

Constant Field Values

Constructor Detail

Segment

public Segment(SegmentTracker tracker,
       SegmentId id,
       ByteBuffer data)

Segment

public Segment(SegmentTracker tracker,
       SegmentId id,
       ByteBuffer data,
       SegmentVersion version)

Method Detail

decode

public static int decode(short offset)

Decode a 4 byte aligned segment offset.

Parameters:

offset - 4 byte aligned segment offset

Returns:

decoded segment offset

encode

public static short encode(int offset)

Encode a segment offset into a 4 byte aligned address packed into a short.

Parameters:

offset - segment offset

Returns:

encoded segment offset packed into a short

align

public static int align(int address,
        int boundary)

Align an address on the given boundary

Parameters:

address - address to align

boundary - boundary to align to

Returns:

n = address + a such that n % boundary == 0 and 0 <= a < boundary.

getSegmentId

public SegmentId getSegmentId()

getRootCount

public int getRootCount()

getRootType

public RecordType getRootType(int index)

getRootOffset

public int getRootOffset(int index)

getSegmentInfo

@CheckForNull
public 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

getReferencedIds

public List<SegmentId> getReferencedIds()

size

public int size()

getCacheSize

public long getCacheSize()

writeTo

public void writeTo(OutputStream stream)
             throws IOException

Writes this segment to the given output stream.

Parameters:

stream - stream to which this segment will be written

Throws:

IOException - on an IO error

toString

public String toString()

Overrides:

toString in class Object