hadoop SequenceFile介绍
2017-07-23 10:57
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SequenceFile是一个由二进制序列化过的key/value的字节流组成的文本存储文件。
基于压缩类型CompressType,共有三种
There are three
based on the CompressType used
to compress key/value pairs:
在SequenceFile里有Writer的实现,源码如下:
存入的文本文件内容如下:
key value
100 One, two, buckle my shoe
99 Three, four, shut the door
98 Five, six, pick up sticks
97 Seven, eight, lay them straight
96 Nine, ten, a big fat hen
95 One, two, buckle my shoe
94 Three, four, shut the door
93 Five, six, pick up sticks
92 Seven, eight, lay them straight
91 Nine, ten, a big fat hen
90 One, two, buckle my shoe
89 Three, four, shut the door
88 Five, six, pick up sticks
87 Seven, eight, lay them straight
86 Nine, ten, a big fat hen
85 One, two, buckle my shoe
84 Three, four, shut the door
83 Five, six, pick up sticks
82 Seven, eight, lay them straight
81 Nine, ten, a big fat hen
80 One, two, buckle my shoe
79 Three, four, shut the door
78 Five, six, pick up sticks
77 Seven, eight, lay them straight
76 Nine, ten, a big fat hen
75 One, two, buckle my shoe
74 Three, four, shut the door
73 Five, six, pick up sticks
72 Seven, eight, lay them straight
71 Nine, ten, a big fat hen
70 One, two, buckle my shoe
69 Three, four, shut the door
68 Five, six, pick up sticks
67 Seven, eight, lay them straight
66 Nine, ten, a big fat hen
65 One, two, buckle my shoe
64 Three, four, shut the door
63 Five, six, pick up sticks
62 Seven, eight, lay them straight
61 Nine, ten, a big fat hen
60 One, two, buckle my shoe
59 Three, four, shut the door
58 Five, six, pick up sticks
57 Seven, eight, lay them straight
56 Nine, ten, a big fat hen
55 One, two, buckle my shoe
54 Three, four, shut the door
53 Five, six, pick up sticks
52 Seven, eight, lay them straight
51 Nine, ten, a big fat hen
50 One, two, buckle my shoe
49 Three, four, shut the door
48 Five, six, pick up sticks
47 Seven, eight, lay them straight
46 Nine, ten, a big fat hen
45 One, two, buckle my shoe
44 Three, four, shut the door
43 Five, six, pick up sticks
42 Seven, eight, lay them straight
41 Nine, ten, a big fat hen
40 One, two, buckle my shoe
39 Three, four, shut the door
38 Five, six, pick up sticks
37 Seven, eight, lay them straight
36 Nine, ten, a big fat hen
35 One, two, buckle my shoe
34 Three, four, shut the door
33 Five, six, pick up sticks
32 Seven, eight, lay them straight
31 Nine, ten, a big fat hen
30 One, two, buckle my shoe
29 Three, four, shut the door
28 Five, six, pick up sticks
27 Seven, eight, lay them straight
26 Nine, ten, a big fat hen
25 One, two, buckle my shoe
24 Three, four, shut the door
23 Five, six, pick up sticks
22 Seven, eight, lay them straight
21 Nine, ten, a big fat hen
20 One, two, buckle my shoe
19 Three, four, shut the door
18 Five, six, pick up sticks
17 Seven, eight, lay them straight
16 Nine, ten, a big fat hen
15 One, two, buckle my shoe
14 Three, four, shut the door
13 Five, six, pick up sticks
12 Seven, eight, lay them straight
11 Nine, ten, a big fat hen
10 One, two, buckle my shoe
9 Three, four, shut the door
8 Five, six, pick up sticks
7 Seven, eight, lay them straight
6 Nine, ten, a big fat hen
5 One, two, buckle my shoe
4 Three, four, shut the door
3 Five, six, pick up sticks
2 Seven, eight, lay them straight
1 Nine, ten, a big fat hen
把以上java 打成jar,执行hadoop jar sfile.jar /test/numbers.seq 1 1代表不压缩
hadoop fs -get hdfs:///test/numbers1.seq /usr/test/ 取出刚刚生成的文件,我们用UE打开看一下
0x53 0x45 0x51
这是SequenceFile Format的magic header「SEQ」,用来区别文本是否是「SequenceFile Format」。
0x06
版本编号,目前最新版为「SEQ6」
以上代码源码如下:
0x20
0x65........0x65
这部份是keyClassName(Key的类名),而第1个Byte(0x20)用来表示此字串的长度,此范例为org.apache.hadoop.io.IntWritable
以上代码源码如下:
0x19
0x6F ..... 0x74
这部份是valueClassName(Value的类名),第1个Byte(0x19)也是用来表示此字串的长度,此范例为org.apache.hadoop.io.BytesWritable
0x00
是否compression?「0x00」=否 (此为Boolean所以佔1个Byte)
0x00
是否blockCompression?「0x00」=否(此为Boolean所以佔1个Byte)
如果是压缩的话接下去还会写压缩类,此范例没有压缩所以没有此类名的写入,源码如下:
0x00 0x00
0x00 0x00
metadata,此范例沒有包含任何metadata, 所以输出「0x00 0x00 0x00 0x00」
0x76
0x61 ..... 0xAF
sync标记,用来表示一个「Header」的结束。
至此头部文件写入完毕,可见头部的格式可以归纳如下:
SequenceFile Header
version - 3 bytes of magic header SEQ, followed by 1 byte of actual version number (e.g. SEQ4 or SEQ6)
keyClassName -key class
valueClassName - value class
compression - A boolean which specifies if compression is turned on for keys/values in this file.
blockCompression - A boolean which specifies if block-compression is turned on for keys/values in this file.
compression codec -
metadata -
sync - A sync marker to denote end of the header.
接下去我们看一下数据存储格式:
0x00 0x00 0x00 0x1D
整个Record的size ,一个Record包含「Key、Value」。此处为29个字节,因为 key=100 占4个字节,value=One, two, buckle my shoe 占24字节 还有一个字节存了value的长度 所以
29字节总共。
0x00 0x00 0x00 0x04
Key內容的size~ (此为Int所以占4个字节)
0x00 0x00 0x00 0x64
Key的内容,此处为100,那十六进制就是64
0x18
value内容的size,此处是One, two, buckle my shoe,长度24 所以十六进制就是18
0x4F 0X6E....0x65
value的内容One, two, buckle my shoe
以上代码源代码如下:
当数据达到一个阀值,会写sync,写sync就是调用checkAndWriteSync();
源码如下:
SYNC_INTERVAL定义如下:
可见每2000byte会写一个sync
SequeceFile 无压缩图示如下:
可见格式如下:
Uncompressed SequenceFile Format
Header
Record
Record length
Key length
Key
Value
接下去我们看一下RecordCompressWriter
执行hadoop jar sfile.jar /test/numbers2.seq 2 2代表使用RecordCompressWriter压缩
同样我们用UE看一下生成的文件:
可见表头和不压缩的基本一致,有些小区别如下:
0x01
代表使用了压缩
0x2A 0x6F ....0x63
使用的压缩类org.apache.hadoop.io.compress.DefaultCodec
0x00 ...0x25
整个Record的size ,为37,为啥比不压缩占用的字节更多?
0x00 0x00 0x00 0x04
Key內容的size~ (此为Int所以占4个字节)
0x00 0x00 0x00 0x64
Key的内容,此处为100,那十六进制就是64 可见key没有压缩
以上源代码如下:
SequeceFile 压缩value图示如下:
可见格式如下:
Record-Compressed SequenceFile Format
Header
Record
Record length
Key length
Key
Compressed Value
接下去我们看一下BlockCompressWriter
执行hadoop jar sfile.jar /test/numbers3.seq 3 3代表使用BlockCompressWriter压缩
同样我们用UE看一下生成的文件:
可见表头和不压缩的基本一致,有些小区别如下:
0x01
代表使用了压缩
0x01
代表使用了block压缩
对于block压缩的源代码如下:
其中,可见没调用一次append,就会相应累加keyLenBuffer和valLenBuffer的长度
WritableUtils.writeVInt(keyLenBuffer, keyLength);
WritableUtils.writeVInt(valLenBuffer, valLength);
int currentBlockSize = keyBuffer.getLength() + valBuffer.getLength();
if (currentBlockSize >= compressionBlockSize) {
sync();
}
compressionBlockSize = conf.getInt("io.seqfile.compress.blocksize", 1000000);
当超过compressionBlockSize是会调用sync,我们来看看sync的源码,如下:
Sequenc File ,块压缩图示如下:
可见格式如下:
Block-Compressed SequenceFile Format
Header
Record Block
Uncompressed number of records in the block
Compressed key-lengths block-size
Compressed key-lengths block
Compressed keys block-size
Compressed keys block
Compressed value-lengths block-size
Compressed value-lengths block
Compressed values block-size
Compressed values block
A sync-marker every block.
本文出自 “软件开发” 博客出处http://tangjj.blog.51cto.com/1848040/1532915
转自:http://tangjj.blog.51cto.com/1848040/1532915
基于压缩类型CompressType,共有三种
SequenceFile
Writer:
SequenceFile
Writers
based on the CompressType used
to compress key/value pairs:
1、Writer: Uncompressed records.
在SequenceFile里有Writer的实现,源码如下:
首先SequenceFile文件有个表头,以上是写表头的代码,我们以一个实例结合代码来看一下表头的组成。
key value
100 One, two, buckle my shoe
99 Three, four, shut the door
98 Five, six, pick up sticks
97 Seven, eight, lay them straight
96 Nine, ten, a big fat hen
95 One, two, buckle my shoe
94 Three, four, shut the door
93 Five, six, pick up sticks
92 Seven, eight, lay them straight
91 Nine, ten, a big fat hen
90 One, two, buckle my shoe
89 Three, four, shut the door
88 Five, six, pick up sticks
87 Seven, eight, lay them straight
86 Nine, ten, a big fat hen
85 One, two, buckle my shoe
84 Three, four, shut the door
83 Five, six, pick up sticks
82 Seven, eight, lay them straight
81 Nine, ten, a big fat hen
80 One, two, buckle my shoe
79 Three, four, shut the door
78 Five, six, pick up sticks
77 Seven, eight, lay them straight
76 Nine, ten, a big fat hen
75 One, two, buckle my shoe
74 Three, four, shut the door
73 Five, six, pick up sticks
72 Seven, eight, lay them straight
71 Nine, ten, a big fat hen
70 One, two, buckle my shoe
69 Three, four, shut the door
68 Five, six, pick up sticks
67 Seven, eight, lay them straight
66 Nine, ten, a big fat hen
65 One, two, buckle my shoe
64 Three, four, shut the door
63 Five, six, pick up sticks
62 Seven, eight, lay them straight
61 Nine, ten, a big fat hen
60 One, two, buckle my shoe
59 Three, four, shut the door
58 Five, six, pick up sticks
57 Seven, eight, lay them straight
56 Nine, ten, a big fat hen
55 One, two, buckle my shoe
54 Three, four, shut the door
53 Five, six, pick up sticks
52 Seven, eight, lay them straight
51 Nine, ten, a big fat hen
50 One, two, buckle my shoe
49 Three, four, shut the door
48 Five, six, pick up sticks
47 Seven, eight, lay them straight
46 Nine, ten, a big fat hen
45 One, two, buckle my shoe
44 Three, four, shut the door
43 Five, six, pick up sticks
42 Seven, eight, lay them straight
41 Nine, ten, a big fat hen
40 One, two, buckle my shoe
39 Three, four, shut the door
38 Five, six, pick up sticks
37 Seven, eight, lay them straight
36 Nine, ten, a big fat hen
35 One, two, buckle my shoe
34 Three, four, shut the door
33 Five, six, pick up sticks
32 Seven, eight, lay them straight
31 Nine, ten, a big fat hen
30 One, two, buckle my shoe
29 Three, four, shut the door
28 Five, six, pick up sticks
27 Seven, eight, lay them straight
26 Nine, ten, a big fat hen
25 One, two, buckle my shoe
24 Three, four, shut the door
23 Five, six, pick up sticks
22 Seven, eight, lay them straight
21 Nine, ten, a big fat hen
20 One, two, buckle my shoe
19 Three, four, shut the door
18 Five, six, pick up sticks
17 Seven, eight, lay them straight
16 Nine, ten, a big fat hen
15 One, two, buckle my shoe
14 Three, four, shut the door
13 Five, six, pick up sticks
12 Seven, eight, lay them straight
11 Nine, ten, a big fat hen
10 One, two, buckle my shoe
9 Three, four, shut the door
8 Five, six, pick up sticks
7 Seven, eight, lay them straight
6 Nine, ten, a big fat hen
5 One, two, buckle my shoe
4 Three, four, shut the door
3 Five, six, pick up sticks
2 Seven, eight, lay them straight
1 Nine, ten, a big fat hen
把以上java 打成jar,执行hadoop jar sfile.jar /test/numbers.seq 1 1代表不压缩
hadoop fs -get hdfs:///test/numbers1.seq /usr/test/ 取出刚刚生成的文件,我们用UE打开看一下
0x53 0x45 0x51
这是SequenceFile Format的magic header「SEQ」,用来区别文本是否是「SequenceFile Format」。
0x06
版本编号,目前最新版为「SEQ6」
以上代码源码如下:
0x65........0x65
这部份是keyClassName(Key的类名),而第1个Byte(0x20)用来表示此字串的长度,此范例为org.apache.hadoop.io.IntWritable
以上代码源码如下:
0x6F ..... 0x74
这部份是valueClassName(Value的类名),第1个Byte(0x19)也是用来表示此字串的长度,此范例为org.apache.hadoop.io.BytesWritable
是否compression?「0x00」=否 (此为Boolean所以佔1个Byte)
0x00
是否blockCompression?「0x00」=否(此为Boolean所以佔1个Byte)
0x00 0x00
metadata,此范例沒有包含任何metadata, 所以输出「0x00 0x00 0x00 0x00」
0x61 ..... 0xAF
sync标记,用来表示一个「Header」的结束。
SequenceFile Header
version - 3 bytes of magic header SEQ, followed by 1 byte of actual version number (e.g. SEQ4 or SEQ6)
keyClassName -key class
valueClassName - value class
compression - A boolean which specifies if compression is turned on for keys/values in this file.
blockCompression - A boolean which specifies if block-compression is turned on for keys/values in this file.
compression codec -
CompressionCodecclass which is used for compression of keys and/or values (if compression is enabled).
metadata -
Metadatafor this file.
sync - A sync marker to denote end of the header.
接下去我们看一下数据存储格式:
0x00 0x00 0x00 0x1D
整个Record的size ,一个Record包含「Key、Value」。此处为29个字节,因为 key=100 占4个字节,value=One, two, buckle my shoe 占24字节 还有一个字节存了value的长度 所以
29字节总共。
0x00 0x00 0x00 0x04
Key內容的size~ (此为Int所以占4个字节)
0x00 0x00 0x00 0x64
Key的内容,此处为100,那十六进制就是64
0x18
value内容的size,此处是One, two, buckle my shoe,长度24 所以十六进制就是18
0x4F 0X6E....0x65
value的内容One, two, buckle my shoe
以上代码源代码如下:
源码如下:
SequeceFile 无压缩图示如下:
可见格式如下:
Uncompressed SequenceFile Format
Header
Record
Record length
Key length
Key
Value
接下去我们看一下RecordCompressWriter
2、RecordCompressWriter: Record-compressed files, only compress values.
执行hadoop jar sfile.jar /test/numbers2.seq 2 2代表使用RecordCompressWriter压缩
同样我们用UE看一下生成的文件:
可见表头和不压缩的基本一致,有些小区别如下:
0x01
代表使用了压缩
0x2A 0x6F ....0x63
使用的压缩类org.apache.hadoop.io.compress.DefaultCodec
0x00 ...0x25
整个Record的size ,为37,为啥比不压缩占用的字节更多?
0x00 0x00 0x00 0x04
Key內容的size~ (此为Int所以占4个字节)
0x00 0x00 0x00 0x64
Key的内容,此处为100,那十六进制就是64 可见key没有压缩
以上源代码如下:
可见格式如下:
Record-Compressed SequenceFile Format
Header
Record
Record length
Key length
Key
Compressed Value
接下去我们看一下BlockCompressWriter
3、BlockCompressWriter: Block-compressed files, both keys & values are collected in 'blocks' separately and compressed. The size of the 'block' is configurable.
执行hadoop jar sfile.jar /test/numbers3.seq 3 3代表使用BlockCompressWriter压缩
同样我们用UE看一下生成的文件:
可见表头和不压缩的基本一致,有些小区别如下:
0x01
代表使用了压缩
0x01
代表使用了block压缩
对于block压缩的源代码如下:
WritableUtils.writeVInt(keyLenBuffer, keyLength);
WritableUtils.writeVInt(valLenBuffer, valLength);
int currentBlockSize = keyBuffer.getLength() + valBuffer.getLength();
if (currentBlockSize >= compressionBlockSize) {
sync();
}
compressionBlockSize = conf.getInt("io.seqfile.compress.blocksize", 1000000);
当超过compressionBlockSize是会调用sync,我们来看看sync的源码,如下:
可见格式如下:
Block-Compressed SequenceFile Format
Header
Record Block
Uncompressed number of records in the block
Compressed key-lengths block-size
Compressed key-lengths block
Compressed keys block-size
Compressed keys block
Compressed value-lengths block-size
Compressed value-lengths block
Compressed values block-size
Compressed values block
A sync-marker every block.
本文出自 “软件开发” 博客出处http://tangjj.blog.51cto.com/1848040/1532915
转自:http://tangjj.blog.51cto.com/1848040/1532915
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