/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.hadoop.hbase;
import org.apache.hadoop.hbase.classification.InterfaceAudience;
/**
* The unit of storage in HBase consisting of the following fields:
* <br>
* <pre>
* 1) row
* 2) column family
* 3) column qualifier
* 4) timestamp
* 5) type
* 6) MVCC version
* 7) value
* </pre>
* <p>
* Uniqueness is determined by the combination of row, column family, column qualifier,
* timestamp, and type.
* </p>
* <p>
* 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.
* </p>
* <p>
* 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.
* </p>
* <p>
* 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[].
* </p>
* <p>
* 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.
* </p>
*/
@InterfaceAudience.Public
public interface Cell {
//1) Row
/**
* Contiguous raw bytes that may start at any index in the containing array. Max length is
* Short.MAX_VALUE which is 32,767 bytes.
* @return The array containing the row bytes.
*/
byte[] getRowArray();
/**
* @return Array index of first row byte
*/
int getRowOffset();
/**
* @return Number of row bytes. Must be < rowArray.length - offset.
*/
short getRowLength();
//2) Family
/**
* 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.
* @return the array containing the family bytes.
*/
byte[] getFamilyArray();
/**
* @return Array index of first family byte
*/
int getFamilyOffset();
/**
* @return Number of family bytes. Must be < familyArray.length - offset.
*/
byte getFamilyLength();
//3) Qualifier
/**
* Contiguous raw bytes that may start at any index in the containing array.
* @return The array containing the qualifier bytes.
*/
byte[] getQualifierArray();
/**
* @return Array index of first qualifier byte
*/
int getQualifierOffset();
/**
* @return Number of qualifier bytes. Must be < qualifierArray.length - offset.
*/
int getQualifierLength();
//4) Timestamp
/**
* @return 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.
*/
long getTimestamp();
//5) Type
/**
* @return The byte representation of the KeyValue.TYPE of this cell: one of Put, Delete, etc
*/
byte getTypeByte();
//6) SequenceId
/**
* 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
* {@link 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.
* @return seqId (always > 0 if exists), or 0 if it no longer exists
*/
long getSequenceId();
//7) Value
/**
* 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.
* @return The array containing the value bytes.
*/
byte[] getValueArray();
/**
* @return Array index of first value byte
*/
int getValueOffset();
/**
* @return Number of value bytes. Must be < valueArray.length - offset.
*/
int getValueLength();
/**
* Contiguous raw bytes representing tags that may start at any index in the containing array.
* @return the tags byte array
*/
byte[] getTagsArray();
/**
* @return the first offset where the tags start in the Cell
*/
int getTagsOffset();
/**
* 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 {@link 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.
*
* @return the total length of the tags in the Cell.
*/
int getTagsLength();
}