MySQL Innodb 存储结构 和 存储Null值 用法详解
背景:
表空间:INNODB 所有数据都存在表空间当中(共享表空间),要是开启innodb_file_per_table,则每张表的数据会存到单独的一个表空间内(独享表空间)。独享表空间包括:数据,索引,插入缓存,数据字典。共享表空间包括:Undo信息(不会回收<物理空间上>),双写缓存信息,事务信息等。段(segment):组成表空间,有区组成。区(extent):有64个连续的页组成。每个页16K,总共1M。对于大的数据段,每次最后可申请4个区。页(page):是INNODB 磁盘管理的单位,有行组成。行(row):包括事务ID,回滚指针,列信息等。
目的1:了解表空间各个页的信息和溢出行数据存储的信息。通过该书作者蒋承尧编写的工具:http://code.google.com/p/david-mysql-tools/source/browse/trunk/py_innodb_page_type/3个脚本:
py_innodb_page_info.py
View Code #! /usr/bin/env python #encoding=utf-8import mylibfrom sys import argvfrom mylib import myargvif __name__ == ’__main__’: myargv = myargv(argv) if myargv.parse_cmdline() == 0: pass else: mylib.get_innodb_page_type(myargv)
mylib.py
View Code encoding=utf-8import osimport includefrom include import *TABLESPACE_NAME=’D:mysql_datatestt.ibd’VARIABLE_FIELD_COUNT = 1NULL_FIELD_COUNT = 0class myargv(object): def __init__(self, argv): self.argv = argv self.parms = {} self.tablespace = ’’ def parse_cmdline(self): argv = self.argv if len(argv) == 1: print ’Usage: python py_innodb_page_info.py [OPTIONS] tablespace_file’ print ’For more options, use python py_innodb_page_info.py -h’ return 0 while argv: if argv[0][0] == ’-’: if argv[0][1] == ’h’: self.parms[argv[0]] = ’’ argv = argv[1:] break if argv[0][1] == ’v’: self.parms[argv[0]] = ’’ argv = argv[1:] else: self.parms[argv[0]] = argv[1] argv = argv[2:] else: self.tablespace = argv[0] argv = argv[1:] if self.parms.has_key(’-h’): print ’Get InnoDB Page Info’ print ’Usage: python py_innodb_page_info.py [OPTIONS] tablespace_filen’ print ’The following options may be given as the first argument:’ print ’-h help ’ print ’-o output put the result to file’ print ’-t number thread to anayle the tablespace file’ print ’-v verbose mode’ return 0 return 1def mach_read_from_n(page,start_offset,length): ret = page[start_offset:start_offset+length] return ret.encode(’hex’)def get_innodb_page_type(myargv): f=file(myargv.tablespace,’rb’) fsize = os.path.getsize(f.name)/INNODB_PAGE_SIZE ret = {} for i in range(fsize): page = f.read(INNODB_PAGE_SIZE) page_offset = mach_read_from_n(page,FIL_PAGE_OFFSET,4) page_type = mach_read_from_n(page,FIL_PAGE_TYPE,2) if myargv.parms.has_key(’-v’): if page_type == ’45bf’: page_level = mach_read_from_n(page,FIL_PAGE_DATA+PAGE_LEVEL,2) print 'page offset %s, page type <%s>, page level <%s>'%(page_offset,innodb_page_type[page_type],page_level) else: print 'page offset %s, page type <%s>'%(page_offset,innodb_page_type[page_type]) if not ret.has_key(page_type): ret[page_type] = 1 else: ret[page_type] = ret[page_type] + 1 print 'Total number of page: %d:'%fsize for type in ret: print '%s: %s'%(innodb_page_type[type],ret[type])
include.py
View Code #encoding=utf-8INNODB_PAGE_SIZE = 16*1024*1024# Start of the data on the pageFIL_PAGE_DATA = 38FIL_PAGE_OFFSET = 4 # page offset inside spaceFIL_PAGE_TYPE = 24 # File page type# Types of an undo log segment */TRX_UNDO_INSERT = 1TRX_UNDO_UPDATE = 2# On a page of any file segment, data may be put starting from this offsetFSEG_PAGE_DATA = FIL_PAGE_DATA# The offset of the undo log page header on pages of the undo logTRX_UNDO_PAGE_HDR = FSEG_PAGE_DATAPAGE_LEVEL = 26 #level of the node in an index tree; the leaf level is the level 0 */innodb_page_type={ ’0000’:u’Freshly Allocated Page’, ’0002’:u’Undo Log Page’, ’0003’:u’File Segment inode’, ’0004’:u’Insert Buffer Free List’, ’0005’:u’Insert Buffer Bitmap’, ’0006’:u’System Page’, ’0007’:u’Transaction system Page’, ’0008’:u’File Space Header’, ’0009’:u’扩展描述页’, ’000a’:u’Uncompressed BLOB Page’, ’000b’:u’1st compressed BLOB Page’, ’000c’:u’Subsequent compressed BLOB Page’, ’45bf’:u’B-tree Node’ }innodb_page_direction={ ’0000’: ’Unknown(0x0000)’, ’0001’: ’Page Left’, ’0002’: ’Page Right’, ’0003’: ’Page Same Rec’, ’0004’: ’Page Same Page’, ’0005’: ’Page No Direction’, ’ffff’: ’Unkown2(0xffff)’}INNODB_PAGE_SIZE=1024*16 # InnoDB Page 16K
测试1:
root@localhost : test 02:26:13>create table tt(id int auto_increment,name varchar(10),age int,address varchar(20),primary key (id))engine=innodb;Query OK, 0 rows affected (0.17 sec)root@zhoujy:/var/lib/mysql/test# ls -lh tt.ibd -rw-rw---- 1 mysql mysql 96K 2012-10-17 14:26 tt.ibd
查看ibd:
root@zhoujy:/home/zhoujy/jiaoben/read_ibd# python py_innodb_page_info.py /var/lib/mysql/test/tt.ibd -vpage offset 00000000, page type <File Space Header>page offset 00000001, page type <Insert Buffer Bitmap>page offset 00000002, page type <File Segment inode>page offset 00000003, page type <B-tree Node>, page level <0000> ---叶子节点page offset 00000000, page type <Freshly Allocated Page>page offset 00000000, page type <Freshly Allocated Page>Total number of page: 6: Freshly Allocated Page: 2Insert Buffer Bitmap: 1File Space Header: 1B-tree Node: 1File Segment inode: 1
解释:Total number of page: 总页数Freshly Allocated Page:可用页Insert Buffer Bitmap:插入缓存位图页Insert Buffer Free List:插入缓存空闲列表页B-tree Node:数据页Uncompressed BLOB Page:二进制大对象页,存放溢出行的页,即溢出页上面得到的信息是表初始化大小为96K,他是有 Total number of page * 16 得来的。1个数据页,2个可用页面。
root@localhost : test 02:42:58>insert into tt values(name,age,address) values(’aaa’,23,’HZZZ’);
疑惑:为什么没有申请区?区是64个连续的页,大小1M。那么表大小也应该是至少1M。但是现在只有96K(默认)。原因是因为每个段开始的时候,先有32个页大小的碎片页存放数据,使用完之后才是64页的连续申请,最多每次可以申请4个区,保证数据的顺序。这里看出表大小增加是按照至少64页的大小的空间来增加的,即1M增加。验证:填充数据,写满这32个碎片页,32*16 = 512K。看看是否能申请大于1M的空间。
View Code root@zhoujy:/home/zhoujy/jiaoben/read_ibd# ls -lh /var/lib/mysql/test/tt.ibd -rw-rw---- 1 mysql mysql 576K 2012-10-17 15:30 /var/lib/mysql/test/tt.ibdroot@zhoujy:/home/zhoujy/jiaoben/read_ibd# python py_innodb_page_info.py /var/lib/mysql/test/tt.ibd -vpage offset 00000000, page type <File Space Header>page offset 00000001, page type <Insert Buffer Bitmap>page offset 00000002, page type <File Segment inode>page offset 00000003, page type <B-tree Node>, page level <0001>page offset 00000004, page type <B-tree Node>, page level <0000>page offset 00000005, page type <B-tree Node>, page level <0000>page offset 00000006, page type <B-tree Node>, page level <0000>page offset 00000007, page type <B-tree Node>, page level <0000>page offset 00000008, page type <B-tree Node>, page level <0000>page offset 00000009, page type <B-tree Node>, page level <0000>page offset 0000000a, page type <B-tree Node>, page level <0000>page offset 0000000b, page type <B-tree Node>, page level <0000>page offset 0000000c, page type <B-tree Node>, page level <0000>page offset 0000000d, page type <B-tree Node>, page level <0000>page offset 0000000e, page type <B-tree Node>, page level <0000>page offset 0000000f, page type <B-tree Node>, page level <0000>page offset 00000010, page type <B-tree Node>, page level <0000>page offset 00000011, page type <B-tree Node>, page level <0000>page offset 00000012, page type <B-tree Node>, page level <0000>page offset 00000013, page type <B-tree Node>, page level <0000>page offset 00000014, page type <B-tree Node>, page level <0000>page offset 00000015, page type <B-tree Node>, page level <0000>page offset 00000016, page type <B-tree Node>, page level <0000>page offset 00000017, page type <B-tree Node>, page level <0000>page offset 00000018, page type <B-tree Node>, page level <0000>page offset 00000019, page type <B-tree Node>, page level <0000>page offset 0000001a, page type <B-tree Node>, page level <0000>page offset 0000001b, page type <B-tree Node>, page level <0000>page offset 0000001c, page type <B-tree Node>, page level <0000>page offset 0000001d, page type <B-tree Node>, page level <0000>page offset 0000001e, page type <B-tree Node>, page level <0000>page offset 0000001f, page type <B-tree Node>, page level <0000>page offset 00000020, page type <B-tree Node>, page level <0000>page offset 00000021, page type <B-tree Node>, page level <0000>page offset 00000022, page type <B-tree Node>, page level <0000>page offset 00000023, page type <B-tree Node>, page level <0000>Total number of page: 36:Insert Buffer Bitmap: 1File Space Header: 1B-tree Node: 33File Segment inode: 1
'额外'页:4个page offset 00000000, page type <File Space Header> :文件头空间页page offset 00000001, page type <Insert Buffer Bitmap>:插入缓存位图页page offset 00000002, page type <File Segment inode>:文件段节点page offset 00000003, page type <B-tree Node>, page level <0001>:根页碎片页:32个page type <B-tree Node>, page level <0000>总共36个页,ibd大小 576K的由来:32*16=512K(碎片页)+ 4*16=64(额外页),这里开始要是再插入的话,应该申请最少1M的页:
root@zhoujy:/home/zhoujy/jiaoben/read_ibd# ls -lh /var/lib/mysql/test/tt.ibd -rw-rw---- 1 mysql mysql 2.0M 2012-10-17 16:10 /var/lib/mysql/test/tt.ibdroot@zhoujy:/home/zhoujy/jiaoben/read_ibd# python py_innodb_page_info.py /var/lib/mysql/test/tt.ibdTotal number of page: 128:Freshly Allocated Page: 91Insert Buffer Bitmap: 1File Space Header: 1B-tree Node: 34File Segment inode: 1
页从36跳到了128,因为已经用完了32个碎片页,新的页会采用区的方式进行空间申请。信息中看到有很多可用页,正好说明这点。
▲溢出行数据存放:INNODB存储引擎是索引组织的,即每页中至少有两行记录,因此如果页中只能存放一行记录,INNODB会自动将行数据放到溢出页中。当发生溢出行的时候,实际数据保存在BLOB页中,数据页只保存数据的前768字节(老的文件格式),新的文件格式(Barracuda)采用完全行溢出的方式,数据页只保存20个字节的指针,BLOB也保存所有数据。如何查看表中有溢出行数据呢?
root@localhost : test 04:52:34>create table t1 (id int,name varchar(10),memo varchar(8000))engine =innodb default charset utf8;Query OK, 0 rows affected (0.16 sec)root@localhost : test 04:53:10>insert into t1 values(1,’zjy’,repeat(’我’,8000));Query OK, 1 row affected (0.00 sec)
查看ibd:
root@zhoujy:/home/zhoujy/jiaoben/read_ibd# python py_innodb_page_info.py /var/lib/mysql/test/t1.ibd -vpage offset 00000000, page type <File Space Header>page offset 00000001, page type <Insert Buffer Bitmap>page offset 00000002, page type <File Segment inode>page offset 00000003, page type <B-tree Node>, page level <0000>page offset 00000004, page type <Uncompressed BLOB Page>page offset 00000005, page type <Uncompressed BLOB Page>Total number of page: 6:Insert Buffer Bitmap: 1Uncompressed BLOB Page: 2File Space Header: 1B-tree Node: 1File Segment inode: 1
从信息中看到,刚才插入的一行记录,已经溢出了,保存到了2个BLOB页中(<Uncompressed BLOB Page>)。因为1页只有16K,又要存2行数据,所以每行记录最好小于8K,而上面的远远大于8K,所以被溢出了。当然这个也不是包括特大字段,要是一张表里面有5个字段都是varchar(512)【多个varchar的总和大于8K就可以】,也会溢出:
root@localhost : test 05:08:39>create table t2 (id int,name varchar(1000),address varchar(512),company varchar(200),xx varchar(512),memo varchar(512),dem varchar(1000))engine =innodb default charset utf8;Query OK, 0 rows affected (0.17 sec)root@localhost : test 05:08:43>insert into t2 values(1,repeat(’周’,1000),repeat(’我’,500),repeat(’丁’,500),repeat(’啊’,500),repeat(’噢’,500),repeat(’阿a’,500));
1000+500+500+500+500+500=3500*3>8000字节;行会被溢出:
root@zhoujy:/home/zhoujy/jiaoben/read_ibd# python py_innodb_page_info.py /var/lib/mysql/test/t2.ibd -vpage offset 00000000, page type <File Space Header>page offset 00000001, page type <Insert Buffer Bitmap>page offset 00000002, page type <File Segment inode>page offset 00000003, page type <B-tree Node>, page level <0000>page offset 00000004, page type <Uncompressed BLOB Page>page offset 00000000, page type <Freshly Allocated Page>Total number of page: 6:Insert Buffer Bitmap: 1Freshly Allocated Page: 1File Segment inode: 1B-tree Node: 1File Space Header: 1Uncompressed BLOB Page: 1
<Uncompressed BLOB Page> 页存放真正的数据,那数据页到底存放什么?用hexdump查看:
root@zhoujy:/home/zhoujy/jiaoben/read_ibd# hexdump -C -v /var/lib/mysql/test/t1.ibd > t1.txt
查看ibd:
View Code 3082 0000c090 00 32 01 10 80 00 00 01 7a 6a 79 e6 88 91 e6 88 |.2......zjy.....|3083 0000c0a0 91 e6 88 91 e6 88 91 e6 88 91 e6 88 91 e6 88 91 |................|3084 0000c0b0 e6 88 91 e6 88 91 e6 88 91 e6 88 91 e6 88 91 e6 |................|3085 0000c0c0 88 91 e6 88 91 e6 88 91 e6 88 91 e6 88 91 e6 88 |................|3086 0000c0d0 91 e6 88 91 e6 88 91 e6 88 91 e6 88 91 e6 88 91 |................|3087 0000c0e0 e6 88 91 e6 88 91 e6 88 91 e6 88 91 e6 88 91 e6 |................|3088 0000c0f0 88 91 e6 88 91 e6 88 91 e6 88 91 e6 88 91 e6 88 |................|3089 0000c100 91 e6 88 91 e6 88 91 e6 88 91 e6 88 91 e6 88 91 |................|3090 0000c110 e6 88 91 e6 88 91 e6 88 91 e6 88 91 e6 88 91 e6 |................|3091 0000c120 88 91 e6 88 91 e6 88 91 e6 88 91 e6 88 91 e6 88 |................|3092 0000c130 91 e6 88 91 e6 88 91 e6 88 91 e6 88 91 e6 88 91 |................|3093 0000c140 e6 88 91 e6 88 91 e6 88 91 e6 88 91 e6 88 91 e6 |................|3094 0000c150 88 91 e6 88 91 e6 88 91 e6 88 91 e6 88 91 e6 88 |................|3095 0000c160 91 e6 88 91 e6 88 91 e6 88 91 e6 88 91 e6 88 91 |................|3096 0000c170 e6 88 91 e6 88 91 e6 88 91 e6 88 91 e6 88 91 e6 |................|3097 0000c180 88 91 e6 88 91 e6 88 91 e6 88 91 e6 88 91 e6 88 |................|3098 0000c190 91 e6 88 91 e6 88 91 e6 88 91 e6 88 91 e6 88 91 |................|3099 0000c1a0 e6 88 91 e6 88 91 e6 88 91 e6 88 91 e6 88 91 e6 |................|3100 0000c1b0 88 91 e6 88 91 e6 88 91 e6 88 91 e6 88 91 e6 88 |................|3101 0000c1c0 91 e6 88 91 e6 88 91 e6 88 91 e6 88 91 e6 88 91 |................|3102 0000c1d0 e6 88 91 e6 88 91 e6 88 91 e6 88 91 e6 88 91 e6 |................|3103 0000c1e0 88 91 e6 88 91 e6 88 91 e6 88 91 e6 88 91 e6 88 |................|3104 0000c1f0 91 e6 88 91 e6 88 91 e6 88 91 e6 88 91 e6 88 91 |................|3105 0000c200 e6 88 91 e6 88 91 e6 88 91 e6 88 91 e6 88 91 e6 |................|3106 0000c210 88 91 e6 88 91 e6 88 91 e6 88 91 e6 88 91 e6 88 |................|3107 0000c220 91 e6 88 91 e6 88 91 e6 88 91 e6 88 91 e6 88 91 |................|3108 0000c230 e6 88 91 e6 88 91 e6 88 91 e6 88 91 e6 88 91 e6 |................|3109 0000c240 88 91 e6 88 91 e6 88 91 e6 88 91 e6 88 91 e6 88 |................|3110 0000c250 91 e6 88 91 e6 88 91 e6 88 91 e6 88 91 e6 88 91 |................|3111 0000c260 e6 88 91 e6 88 91 e6 88 91 e6 88 91 e6 88 91 e6 |................|3112 0000c270 88 91 e6 88 91 e6 88 91 e6 88 91 e6 88 91 e6 88 |................|3113 0000c280 91 e6 88 91 e6 88 91 e6 88 91 e6 88 91 e6 88 91 |................|3114 0000c290 e6 88 91 e6 88 91 e6 88 91 e6 88 91 e6 88 91 e6 |................|3115 0000c2a0 88 91 e6 88 91 e6 88 91 e6 88 91 e6 88 91 e6 88 |................|3116 0000c2b0 91 e6 88 91 e6 88 91 e6 88 91 e6 88 91 e6 88 91 |................|3117 0000c2c0 e6 88 91 e6 88 91 e6 88 91 e6 88 91 e6 88 91 e6 |................|3118 0000c2d0 88 91 e6 88 91 e6 88 91 e6 88 91 e6 88 91 e6 88 |................|3119 0000c2e0 91 e6 88 91 e6 88 91 e6 88 91 e6 88 91 e6 88 91 |................|3120 0000c2f0 e6 88 91 e6 88 91 e6 88 91 e6 88 91 e6 88 91 e6 |................|3121 0000c300 88 91 e6 88 91 e6 88 91 e6 88 91 e6 88 91 e6 88 |................|3122 0000c310 91 e6 88 91 e6 88 91 e6 88 91 e6 88 91 e6 88 91 |................|3123 0000c320 e6 88 91 e6 88 91 e6 88 91 e6 88 91 e6 88 91 e6 |................|3124 0000c330 88 91 e6 88 91 e6 88 91 e6 88 91 e6 88 91 e6 88 |................|3125 0000c340 91 e6 88 91 e6 88 91 e6 88 91 e6 88 91 e6 88 91 |................|3126 0000c350 e6 88 91 e6 88 91 e6 88 91 e6 88 91 e6 88 91 e6 |................|3127 0000c360 88 91 e6 88 91 e6 88 91 e6 88 91 e6 88 91 e6 88 |................|3128 0000c370 91 e6 88 91 e6 88 91 e6 88 91 e6 88 91 e6 88 91 |................|3129 0000c380 e6 88 91 e6 88 91 e6 88 91 e6 88 91 e6 88 91 e6 |................|3130 0000c390 88 91 e6 88 91 e6 88 91 e6 88 91 00 00 02 1c 00 |................|
文本中刚好是48行,每行16字节。48*16=768字节,刚好验证了之前说的:数据页只保存数据的前768字节(老的文件格式)。
总结1:通过上面的信息,可以能清楚的知道ibd表空间各个页的分布和利用信息以及表空间大小增加的步长;特别注意的是溢出行,一个页中至少包含2行数据,如果页中存放的行数越多,性能就越好。
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目的2:了解表空间如何存储数据,以及对NULL值的存储。
测试2:在测试前先了解INNODB的存储格式(row_format)。老格式(Antelope):Compact<默认>,Redumdant;新格式(Barracuda):Compressed,Dynamic。这里测试指针对默认的存储格式。Compact行记录方式如下:
|变长字段长度列表(1~2字节)|NULL标志位(1字节)|记录头信息(5字节)|RowID(6字节)|事务ID(6字节)|回滚指针(7字节)|
上面信息除了 'NULL标志位'[表中所有字段都定义为NOT NULL],'RowID'[表中有主键] ,'变长字段长度列表' [没有变长字段] 可能不存在外,其他信息都会出现。所以一行数据除了列数据所占用的字段外,还需要额外18字节。
一:字段全NULL
mysql> create table mytest(t1 varchar(10),t2 varchar(10),t3 varchar(10) ,t4 varchar(10))engine=innodb charset = latin1 row_format=compact;Query OK, 0 rows affected (0.08 sec)mysql> insert into mytest values(’a’,’bb’,’bb’,’ccc’);Query OK, 1 row affected (0.02 sec)mysql> insert into mytest values(’a’,’ee’,’ee’,’fff’);Query OK, 1 row affected (0.01 sec)mysql> insert into mytest values(’a’,NULL,NULL,’fff’);Query OK, 1 row affected (0.00 sec)
测试数据准备完之后,执行shell命令:
root@zhoujy:/usr/local/mysql/test# hexdump -C -v mytest.ibd > /home/zhoujy/mytest.txt
打开mytest.txt文件找到supremum这一行:
0000c070 73 75 70 72 65 6d 75 6d 03 02 02 01 00 00 00 10 |supremum........| ----------->一行,16字节0000c080 00 25 00 00 00 03 b9 00 00 00 00 02 49 01 82 00 |.%..........I...|0000c090 00 01 4a 01 10 61 62 62 62 62 63 63 63 03 02 02 |..J..abbbbccc...|0000c0a0 01 00 00 00 18 00 23 00 00 00 03 b9 01 00 00 00 |......#.........|0000c0b0 02 49 02 83 00 00 01 4b 01 10 61 65 65 65 65 66 |.I.....K..aeeeef|0000c0c0 66 66 03 01 06 00 00 20 ff a6 00 00 00 03 b9 02 |ff..... ........|0000c0d0 00 00 00 02 49 03 84 00 00 01 4c 01 10 61 66 66 |....I.....L..aff|0000c0e0 66 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |f...............|
解释:第一行数据:03 02 02 01/*变长字段*/ ---- 表中4个字段类型为varchar,并且没有NULL数据,而且每个字段君小于255。00 /*NULL标志位,第一行没有null的数据*/00 00 10 00 25 /*记录头信息,固定5个字节*/00 00 00 03 b9 00/*RowID,固定6个字节,表没有主键*/00 00 00 02 49 01 /*事务ID,固定6个字节*/82 00 00 01 4a 01 10 /*回滚指针,固定7个字节*/61 62 62 62 62 63 63 63/*列的数据*/第二行数据和第一行数据一样(颜色匹配)。第三行数据(有NULL值)和第一行的解释的颜色对应起来比较差别:
03 02 02 01 VS 03 01 ----------当值为NULL时,变长字段列表不会占用存储空间。61 62 62 62 62 63 63 63 VS 61 66 66 66 --------- NULL值没有存储,不占空间
结论:当值为NULL时,变长字段列表不会占用存储空间。NULL值没有存储,不占空间,但是需要一个标志位(一行一个)。
二:字段全NOT NULL
mysql> create table mytest(t1 varchar(10) NOT NULL,t2 varchar(10) NOT NULL,t3 varchar(10) NOT NULL,t4 varchar(10) NOT NULL)engine=innodb charset = latin1 row_format=compact;Query OK, 0 rows affected (0.03 sec)mysql> insert into mytest values(’a’,’bb’,’bb’,’ccc’);Query OK, 1 row affected (0.01 sec)mysql> insert into mytest values(’a’,’ee’,’ee’,’fff’);Query OK, 1 row affected (0.01 sec)mysql> insert into mytest values(’a’,NULL,NULL,’fff’);ERROR 1048 (23000): Column ’t2’ cannot be null
步骤和上面一样,得到的ibd的结果是:
0000c070 73 75 70 72 65 6d 75 6d 03 02 02 01 00 00 10 00 |supremum........|0000c080 24 00 00 00 03 b9 03 00 00 00 02 49 07 87 00 00 |$..........I....|0000c090 01 4f 01 10 61 62 62 62 62 63 63 63 03 02 02 01 |.O..abbbbccc....|0000c0a0 00 00 18 ff cb 00 00 00 03 b9 04 00 00 00 02 49 |...............I|0000c0b0 08 88 00 00 01 50 01 10 61 65 65 65 65 66 66 66 |.....P..aeeeefff|
和上面比较,发现少了NULL的标志位信息。结论: NULL值会有额外的空间来存储,即每行1字节的大小。对于相同数据的表,字段中有NULL值的表比NOT NULL的大。
三:1个NULL,和1个’’的数据:
mysql> create table mytest(t1 varchar(10) NOT NULL,t2 varchar(10) NOT NULL DEFAULT ’’,t3 varchar(10) NOT NULL ,t4 varchar(10))engine=innodb charset = latin1 row_format=compact;Query OK, 0 rows affected (0.02 sec)mysql> insert into mytest(t1,t2) values(’A’,’BB’);Query OK, 1 row affected, 1 warning (0.01 sec)
步骤和上面一样,得到的ibd的结果是:
0000c070 73 75 70 72 65 6d 75 6d 00 02 01 01 00 00 10 ff |supremum........|0000c080 ef 00 00 00 43 b9 03 00 00 00 02 4a 15 90 00 00 |....C......J....|0000c090 01 c2 01 10 41 42 42 00 00 00 00 00 00 00 00 00 |....ABB.........|
和上面2个区别主要在于变长列表和列数据这里。
结论:列数据信息里表明了 NULL数据和’’数据都不占用任何空间,对于变长字段列表的信息,和一对比得出:‘’数据虽然不需要占用任何存储空间,但是在变长字段列表里面还是需要占用一个字节<毕竟还是一个‘’值>,NULL值不需要占用”,只是NULL会有额外的一个标志位,所以能有个优化的说法:“数据库表中能设置NOT NULL的就尽量设置为NOT NULL,除非确实需要NULL值得。” 在此得到了证明。
上面的测试都是针对VARCHAR的变长类型,那对于CHAR呢?
CHAR 测试:
root@localhost : test 10:33:35>create table mytest(t1 char(10),t2 char(10),t3 char(10) ,t4 char(10))engine=innodb charset = latin1 row_format=compact;Query OK, 0 rows affected (0.16 sec)root@localhost : test 10:33:59>insert into mytest values(’a’,’bb’,’bb’,’ccc’);Query OK, 1 row affected (0.00 sec)root@localhost : test 10:34:09>insert into mytest values(’a’,’ee’,’ee’,’fff’);Query OK, 1 row affected (0.00 sec)root@localhost : test 10:34:19>insert into mytest values(’a’,NULL,NULL,’fff’);Query OK, 1 row affected (0.00 sec)
打开ibd生成的文件:
0000c060 02 00 1b 69 6e 66 69 6d 75 6d 00 04 00 0b 00 00 |...infimum......|0000c070 73 75 70 72 65 6d 75 6d 00 00 00 10 00 41 00 00 |supremum.....A..|0000c080 00 0a f5 00 00 00 00 81 2d 07 80 00 00 00 32 01 |........-.....2.|0000c090 10 61 20 20 20 20 20 20 20 20 20 62 62 20 20 20 |.a bb |0000c0a0 20 20 20 20 20 62 62 20 20 20 20 20 20 20 20 63 | bb c|0000c0b0 63 63 20 20 20 20 20 20 20 00 00 00 18 00 41 00 |cc .....A.|0000c0c0 00 00 0a f5 01 00 00 00 81 2d 08 80 00 00 00 32 |.........-.....2|0000c0d0 01 10 61 20 20 20 20 20 20 20 20 20 65 65 20 20 |..a ee |0000c0e0 20 20 20 20 20 20 65 65 20 20 20 20 20 20 20 20 | ee |0000c0f0 66 66 66 20 20 20 20 20 20 20 06 00 00 20 ff 70 |fff ... .p|0000c100 00 00 00 0a f5 02 00 00 00 81 2d 09 80 00 00 00 |..........-.....|0000c110 32 01 10 61 20 20 20 20 20 20 20 20 20 66 66 66 |2..a fff|0000c120 20 20 20 20 20 20 20 00 00 00 00 00 00 00 00 00 | .........|
和一的varchar比较发现:少了变长字段列表,但是对于char来讲,需要固定长度来存储的,存不到固定长度,也会被填充满。如:20;并且NULL值也不需要占用存储空间。
混合(varchar,char):
root@localhost : test 11:21:48>create table mytest(t1 int,t2 char(10),t3 varchar(10) ,t4 char(10))engine=innodb charset = latin1 row_format=compact;Query OK, 0 rows affected (0.17 sec)root@localhost : test 11:21:50>insert into mytest values(1,’a’,’b’,’c’);Query OK, 1 row affected (0.00 sec)root@localhost : test 11:22:06>insert into mytest values(11,’aa’,’bb’,’cc’);Query OK, 1 row affected (0.00 sec)
从上面的表结构中看出:1,变长字段列表长度:12,NULL标志位:13,记录头信息:54,RowID:65,事务ID:66,回滚指针:7
idb的信息:
0000c070 73 75 70 72 65 6d 75 6d 01 00 00 00 10 00 33 00 |supremum......3.| 0000c080 00 00 0a f5 07 00 00 00 81 2d 1a 80 00 00 00 32 |.........-.....2|0000c090 01 10 80 00 00 01 61 20 20 20 20 20 20 20 20 20 |......a |0000c0a0 62 63 20 20 20 20 20 20 20 20 20 02 00 00 00 18 |bc .....|0000c0b0 ff be 00 00 00 0a f5 08 00 00 00 81 2d 1b 80 00 |............-...|0000c0c0 00 00 32 01 10 80 00 00 0b 61 61 20 20 20 20 20 |..2......aa |0000c0d0 20 20 20 62 62 63 63 20 20 20 20 20 20 20 20 00 | bbcc .|
从上信息得出和之前预料的一样:因为表中只有一个varchar字段,所以,变长列表长度就只有:01 特别注意的是:各个列数据存储的信息:t1字段为int 类型,占用4个字节的大小。第一行:80 00 00 01 就是表示 1 数字;第二行:80 00 00 0b 表示了11的数字。[select hex(11) == B ],其他的和上面的例子一样。
上面都是latin1单字节字符集的说明,那对于多字节字符集的情况怎么样?
root@localhost : test 11:52:10>create table mytest(id int auto_increment,t2 varchar(10),t3 varchar(10) ,t4 char(10),primary key(id))engine=innodb charset = utf8 row_format=compact;Query OK, 0 rows affected (0.17 sec)root@localhost : test 11:52:11>insert into mytest(t2,t3,t4) values(’bb’,’bb’,’ccc’);Query OK, 1 row affected (0.00 sec)root@localhost : test 11:55:34>insert into mytest(t2,t3,t4) values(’我们’,’他们’,’我们的’);Query OK, 1 row affected (0.00 sec)
ibd信息如下:
0000c070 73 75 70 72 65 6d 75 6d 0a 02 02 00 00 00 10 00 |supremum........|0000c080 28 80 00 00 01 00 00 00 81 2d 27 80 00 00 00 32 |(........-’....2|0000c090 01 10 62 62 62 62 63 63 63 20 20 20 20 20 20 20 |..bbbbccc |0000c0a0 0a 06 06 00 00 00 18 ff c7 80 00 00 02 00 00 00 |................|0000c0b0 81 2d 28 80 00 00 00 32 01 10 e6 88 91 e4 bb ac |.-(....2........|0000c0c0 e4 bb 96 e4 bb ac e6 88 91 e4 bb ac e7 9a 84 20 |............... |
因为表有了主键,所以ROWID(6字节)不见了。特别注意的是:变长字段列表是3?表里面的varchar类型的列只有2个啊。经测试得出:在多字节字符集的条件下,char类型被当成可变长度的类型来处理,他们的行存储基本没有区别,所以这个就出现变长列表是3了,因为是utf8字符集,占用三个字节。所以一个汉字均占用了一个页中3个字节的空间(”我们“ :e6 88 91 e4 bb ac)。数据列的信息:id列的1值,应该是 80 00 00 01,为什么这个显示00 32 01 10,而且所有的id都是00 32 01 10。测试发现,id为自增主键的时候,id的4个字节长度都是以00 32 01 10 表示。否则和前面一个例子里说的,用select HEX(X) 表示。
总结2:上面的测试都是基于COMPACT存储格式的,不管是varchar还是char,NULL值是不需要占用存储空间的;特别需要注意的是Redumdant的记录头信息需要6个固定字节;在多字节字符集的条件下,CHAR和VARCHAR的行存储基本是没有区别的。
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