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Common functionality for HBase
/*
* 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.io.encoding;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.nio.ByteBuffer;
import org.apache.hadoop.hbase.classification.InterfaceAudience;
import org.apache.hadoop.hbase.Cell;
import org.apache.hadoop.hbase.KeyValue.KVComparator;
import org.apache.hadoop.hbase.io.hfile.HFileContext;
/**
* Encoding of KeyValue. It aims to be fast and efficient using assumptions:
*
* - the KeyValues are stored sorted by key
* - we know the structure of KeyValue
* - the values are always iterated forward from beginning of block
* - knowledge of Key Value format
*
* It is designed to work fast enough to be feasible as in memory compression.
*/
@InterfaceAudience.Private
public interface DataBlockEncoder {
// TODO: This Interface should be deprecated and replaced. It presumes hfile and carnal knowledge of
// Cell internals. It was done for a different time. Remove. Purge.
/**
* Starts encoding for a block of KeyValues. Call
* {@link #endBlockEncoding(HFileBlockEncodingContext, DataOutputStream, byte[])} to finish
* encoding of a block.
* @param encodingCtx
* @param out
* @throws IOException
*/
void startBlockEncoding(HFileBlockEncodingContext encodingCtx, DataOutputStream out)
throws IOException;
/**
* Encodes a KeyValue.
* @param cell
* @param encodingCtx
* @param out
* @return unencoded kv size written
* @throws IOException
*/
int encode(Cell cell, HFileBlockEncodingContext encodingCtx, DataOutputStream out)
throws IOException;
/**
* Ends encoding for a block of KeyValues. Gives a chance for the encoder to do the finishing
* stuff for the encoded block. It must be called at the end of block encoding.
* @param encodingCtx
* @param out
* @param uncompressedBytesWithHeader
* @throws IOException
*/
void endBlockEncoding(HFileBlockEncodingContext encodingCtx, DataOutputStream out,
byte[] uncompressedBytesWithHeader) throws IOException;
/**
* Decode.
* @param source Compressed stream of KeyValues.
* @param decodingCtx
* @return Uncompressed block of KeyValues.
* @throws IOException If there is an error in source.
*/
ByteBuffer decodeKeyValues(DataInputStream source, HFileBlockDecodingContext decodingCtx)
throws IOException;
/**
* Return first key in block. Useful for indexing. Typically does not make
* a deep copy but returns a buffer wrapping a segment of the actual block's
* byte array. This is because the first key in block is usually stored
* unencoded.
* @param block encoded block we want index, the position will not change
* @return First key in block.
*/
ByteBuffer getFirstKeyInBlock(ByteBuffer block);
/**
* Create a HFileBlock seeker which find KeyValues within a block.
* @param comparator what kind of comparison should be used
* @param decodingCtx
* @return A newly created seeker.
*/
EncodedSeeker createSeeker(KVComparator comparator,
HFileBlockDecodingContext decodingCtx);
/**
* Creates a encoder specific encoding context
*
* @param encoding
* encoding strategy used
* @param headerBytes
* header bytes to be written, put a dummy header here if the header
* is unknown
* @param meta
* HFile meta data
* @return a newly created encoding context
*/
HFileBlockEncodingContext newDataBlockEncodingContext(
DataBlockEncoding encoding, byte[] headerBytes, HFileContext meta);
/**
* Creates an encoder specific decoding context, which will prepare the data
* before actual decoding
*
* @param meta
* HFile meta data
* @return a newly created decoding context
*/
HFileBlockDecodingContext newDataBlockDecodingContext(HFileContext meta);
/**
* An interface which enable to seek while underlying data is encoded.
*
* It works on one HFileBlock, but it is reusable. See
* {@link #setCurrentBuffer(ByteBuffer)}.
*/
interface EncodedSeeker {
/**
* Set on which buffer there will be done seeking.
* @param buffer Used for seeking.
*/
void setCurrentBuffer(ByteBuffer buffer);
/**
* Does a deep copy of the key at the current position. A deep copy is
* necessary because buffers are reused in the decoder.
* @return key at current position
*/
ByteBuffer getKeyDeepCopy();
/**
* Does a shallow copy of the value at the current position. A shallow
* copy is possible because the returned buffer refers to the backing array
* of the original encoded buffer.
* @return value at current position
*/
ByteBuffer getValueShallowCopy();
/**
* @return the KeyValue object at the current position. Includes memstore
* timestamp.
*/
Cell getKeyValue();
/** Set position to beginning of given block */
void rewind();
/**
* Move to next position
* @return true on success, false if there is no more positions.
*/
boolean next();
/**
* Moves the seeker position within the current block to:
*
* - the last key that that is less than or equal to the given key if
*
seekBefore is false
* - the last key that is strictly less than the given key if
* seekBefore is true. The caller is responsible for loading the
* previous block if the requested key turns out to be the first key of the
* current block.
*
* @param key byte array containing the key
* @param offset key position the array
* @param length key length in bytes
* @param seekBefore find the key strictly less than the given key in case
* of an exact match. Does not matter in case of an inexact match.
* @return 0 on exact match, 1 on inexact match.
*/
@Deprecated
int seekToKeyInBlock(
byte[] key, int offset, int length, boolean seekBefore
);
/**
* Moves the seeker position within the current block to:
*
* - the last key that that is less than or equal to the given key if
*
seekBefore is false
* - the last key that is strictly less than the given key if
* seekBefore is true. The caller is responsible for loading the
* previous block if the requested key turns out to be the first key of the
* current block.
*
* @param key - Cell to which the seek should happen
* @param seekBefore find the key strictly less than the given key in case
* of an exact match. Does not matter in case of an inexact match.
* @return 0 on exact match, 1 on inexact match.
*/
int seekToKeyInBlock(Cell key, boolean seekBefore);
/**
* Compare the given key against the current key
* @param comparator
* @param key
* @param offset
* @param length
* @return -1 is the passed key is smaller than the current key, 0 if equal and 1 if greater
*/
public int compareKey(KVComparator comparator, byte[] key, int offset, int length);
public int compareKey(KVComparator comparator, Cell key);
}
}