org.apache.hadoop.hbase

Interface Cell

All Known Subinterfaces:

ExtendedCell

All Known Implementing Classes:

ByteBufferCell, ByteBufferKeyOnlyKeyValue, ByteBufferKeyValue, IndividualBytesFieldCell, KeyValue, KeyValue.KeyOnlyKeyValue, NoTagsByteBufferKeyValue, NoTagsKeyValue, SizeCachedKeyValue, SizeCachedNoTagsKeyValue

@InterfaceAudience.Public
public interface Cell

The unit of storage in HBase consisting of the following fields:

 1) row
 2) column family
 3) column qualifier
 4) timestamp
 5) type
 6) MVCC version
 7) value
 

Uniqueness is determined by the combination of row, column family, column qualifier, timestamp, and type.

The natural comparator will perform a bitwise comparison on row, column family, and column qualifier. Less intuitively, it will then treat the greater timestamp as the lesser value with the goal of sorting newer cells first.

Cell implements Comparable<Cell> which is only meaningful when comparing to other keys in the same table. It uses CellComparator which does not work on the -ROOT- and hbase:meta tables.

In the future, we may consider adding a boolean isOnHeap() method and a getValueBuffer() method that can be used to pass a value directly from an off-heap ByteBuffer to the network without copying into an on-heap byte[].

Historic note: the original Cell implementation (KeyValue) requires that all fields be encoded as consecutive bytes in the same byte[], whereas this interface allows fields to reside in separate byte[]'s.

Method Summary

Modifier and Type	Method and Description
byte[]	getFamilyArray() Contiguous bytes composed of legal HDFS filename characters which may start at any index in the containing array.
byte	getFamilyLength()
int	getFamilyOffset()
byte[]	getQualifierArray() Contiguous raw bytes that may start at any index in the containing array.
int	getQualifierLength()
int	getQualifierOffset()
byte[]	getRowArray() Contiguous raw bytes that may start at any index in the containing array.
short	getRowLength()
int	getRowOffset()
long	getSequenceId() A region-specific unique monotonically increasing sequence ID given to each Cell.
byte[]	getTagsArray() Contiguous raw bytes representing tags that may start at any index in the containing array.
int	getTagsLength() HBase internally uses 2 bytes to store tags length in Cell.
int	getTagsOffset()
long	getTimestamp()
byte	getTypeByte()
byte[]	getValueArray() Contiguous raw bytes that may start at any index in the containing array.
int	getValueLength()
int	getValueOffset()

Method Detail

getRowArray

byte[] getRowArray()

Contiguous raw bytes that may start at any index in the containing array. Max length is Short.MAX_VALUE which is 32,767 bytes.

Returns:

The array containing the row bytes.

getRowOffset

int getRowOffset()

Returns:

Array index of first row byte

getRowLength

short getRowLength()

Returns:

Number of row bytes. Must be < rowArray.length - offset.

getFamilyArray

byte[] getFamilyArray()

Contiguous bytes composed of legal HDFS filename characters which may start at any index in the containing array. Max length is Byte.MAX_VALUE, which is 127 bytes.

Returns:

the array containing the family bytes.

getFamilyOffset

int getFamilyOffset()

Returns:

Array index of first family byte

getFamilyLength

byte getFamilyLength()

Returns:

Number of family bytes. Must be < familyArray.length - offset.

getQualifierArray

byte[] getQualifierArray()

Contiguous raw bytes that may start at any index in the containing array.

Returns:

The array containing the qualifier bytes.

getQualifierOffset

int getQualifierOffset()

Returns:

Array index of first qualifier byte

getQualifierLength

int getQualifierLength()

Returns:

Number of qualifier bytes. Must be < qualifierArray.length - offset.

getTimestamp

long getTimestamp()

Returns:

Long value representing time at which this cell was "Put" into the row. Typically represents the time of insertion, but can be any value from 0 to Long.MAX_VALUE.

getTypeByte

byte getTypeByte()

Returns:

The byte representation of the KeyValue.TYPE of this cell: one of Put, Delete, etc

getSequenceId

long getSequenceId()

A region-specific unique monotonically increasing sequence ID given to each Cell. It always exists for cells in the memstore but is not retained forever. It will be kept for HConstants.KEEP_SEQID_PERIOD days, but generally becomes irrelevant after the cell's row is no longer involved in any operations that require strict consistency.

Returns:

seqId (always > 0 if exists), or 0 if it no longer exists

getValueArray

byte[] getValueArray()

Contiguous raw bytes that may start at any index in the containing array. Max length is Integer.MAX_VALUE which is 2,147,483,647 bytes.

Returns:

The array containing the value bytes.

getValueOffset

int getValueOffset()

Returns:

Array index of first value byte

getValueLength

int getValueLength()

Returns:

Number of value bytes. Must be < valueArray.length - offset.

getTagsArray

byte[] getTagsArray()

Contiguous raw bytes representing tags that may start at any index in the containing array.

Returns:

the tags byte array

getTagsOffset

int getTagsOffset()

Returns:

the first offset where the tags start in the Cell

getTagsLength

int getTagsLength()

HBase internally uses 2 bytes to store tags length in Cell. As the tags length is always a non-negative number, to make good use of the sign bit, the max of tags length is defined as TagUtil.MAX_TAGS_LENGTH, which is 2 * Short.MAX_VALUE + 1 = 65535. As a result, the return type is int, because a short is not capable of handling that. Please note that even if the return type is int, the max tags length is far less than Integer.MAX_VALUE.

Returns:

the total length of the tags in the Cell.