浅谈MySQL字符集
Preface
MySQL use character set & collation to organize the different charater.It provides a flexible way in setting individual character set on a database,a table even on a single column of table.Each character set has a series of collations with one default collation.We can generally see the character set in MySQL as the combination of code page & character encoding.
In the early version of MySQL(eg. version 5.5) ,latin1 is the default character set which does not support Chinese characters.There're some other commonly used character set such as GBK,UTF-8.MySQL 5.7 chooses UTF-8 as default character set nowadays in order to support more characters of different languages.
Messy code is a general issue about character set.It always occur in our MySQL databases if we do not use character rules appropriately.Worse,it leads to data loss in some cases what is really a big trouble we should avoid.
Introduce
MySQL provides a lot of parameters to specify character set in various dimentionality.We should know clearly about the principle and function of each parameter to avert underlying messy code issue.Let's see details about it.
Procedure
Check the character set supported by MySQL(version 5.7).
(root@localhost mysql3306.sock)[(none)]>show character set;
+----------+---------------------------------+---------------------+--------+
| Charset | Description | Default collation | Maxlen |
+----------+---------------------------------+---------------------+--------+
| big5 | Big5 Traditional Chinese | big5_chinese_ci | |
| dec8 | DEC West European | dec8_swedish_ci | |
| cp850 | DOS West European | cp850_general_ci | |
| hp8 | HP West European | hp8_english_ci | |
| koi8r | KOI8-R Relcom Russian | koi8r_general_ci | |
| latin1 | cp1252 West European | latin1_swedish_ci | |
| latin2 | ISO - Central European | latin2_general_ci | |
| swe7 | 7bit Swedish | swe7_swedish_ci | |
| ascii | US ASCII | ascii_general_ci | |
| ujis | EUC-JP Japanese | ujis_japanese_ci | |
| sjis | Shift-JIS Japanese | sjis_japanese_ci | |
| hebrew | ISO - Hebrew | hebrew_general_ci | |
| tis620 | TIS620 Thai | tis620_thai_ci | |
| euckr | EUC-KR Korean | euckr_korean_ci | |
| koi8u | KOI8-U Ukrainian | koi8u_general_ci | |
| gb2312 | GB2312 Simplified Chinese | gb2312_chinese_ci | |
| greek | ISO - Greek | greek_general_ci | |
| cp1250 | Windows Central European | cp1250_general_ci | |
| gbk | GBK Simplified Chinese | gbk_chinese_ci | |
| latin5 | ISO - Turkish | latin5_turkish_ci | |
| armscii8 | ARMSCII- Armenian | armscii8_general_ci | |
| utf8 | UTF- Unicode | utf8_general_ci | |
| ucs2 | UCS- Unicode | ucs2_general_ci | |
| cp866 | DOS Russian | cp866_general_ci | |
| keybcs2 | DOS Kamenicky Czech-Slovak | keybcs2_general_ci | |
| macce | Mac Central European | macce_general_ci | |
| macroman | Mac West European | macroman_general_ci | |
| cp852 | DOS Central European | cp852_general_ci | |
| latin7 | ISO - Baltic | latin7_general_ci | |
| utf8mb4 | UTF- Unicode | utf8mb4_general_ci | |
| cp1251 | Windows Cyrillic | cp1251_general_ci | |
| utf16 | UTF- Unicode | utf16_general_ci | |
| utf16le | UTF-16LE Unicode | utf16le_general_ci | |
| cp1256 | Windows Arabic | cp1256_general_ci | |
| cp1257 | Windows Baltic | cp1257_general_ci | |
| utf32 | UTF- Unicode | utf32_general_ci | |
| binary | Binary pseudo charset | binary | |
| geostd8 | GEOSTD8 Georgian | geostd8_general_ci | |
| cp932 | SJIS for Windows Japanese | cp932_japanese_ci | |
| eucjpms | UJIS for Windows Japanese | eucjpms_japanese_ci | |
| gb18030 | China National Standard GB18030 | gb18030_chinese_ci | |
+----------+---------------------------------+---------------------+--------+
rows in set (0.00 sec) //There're 41 results of the supported character set.
//Each character set has a default collation.
//Maxlen is the max bytes of corresponding character set(eg. utf8mb4 supports 4 bytes).
Check character set parameters of current MySQL server.
(root@localhost mysql3306.sock)[(none)]>show variables like 'character%';
+--------------------------+----------------------------------------------------------------+
| Variable_name | Value |
+--------------------------+----------------------------------------------------------------+
| character_set_client | utf8 |
| character_set_connection | utf8 |
| character_set_database | utf8 |
| character_set_filesystem | binary |
| character_set_results | utf8 |
| character_set_server | utf8 |
| character_set_system | utf8 |
| character_sets_dir | /usr/local/mysql-5.7.-linux-glibc2.-x86_64/share/charsets/ |
+--------------------------+----------------------------------------------------------------+
rows in set (0.00 sec) //character_set_client:It's used by client when connect to servers for requesting data.
//character_set_connection:It's used for those literals not have a character set introducer for conversion.
//character_set_database:It's used by default database.The value of "character_set_server" will be inherited if it is not specified.
//character_set_filesystem:It's used to interpret string literals refer to file names.
//character_set_results:It's used to return query results to the client.
//character_set_server:It's the default character set of server.
//character_set_system:It's used by server for storing identifiers,the value is utf8 forever.
//character_sets_dir:It's the directory where contains the xml files of installed character set.
The relationship of above character set parameters shows below.
Check collation parameters of current MySQL server.
(root@localhost mysql3306.sock)[(none)]>show variables like 'collation%';
+----------------------+-----------------+
| Variable_name | Value |
+----------------------+-----------------+
| collation_connection | utf8_general_ci |
| collation_database | utf8_general_ci |
| collation_server | utf8_general_ci |
+----------------------+-----------------+
rows in set (0.01 sec) //collation_connection:The collation of connection character set.
//collation_database:The collation of default database.It will inherite the value of "collation_server" if not specified.
//collation_server:The default collation of server.
//"ci" means Case Insensitive.
Case of change character set from utf8 to latin1 with "set names ...;".
(root@localhost mysql3306.sock)[(none)]>\s
--------------
mysql Ver 14.14 Distrib 5.7., for linux-glibc2. (x86_64) using EditLine wrapper Connection id:
Current database:
Current user: root@localhost
SSL: Not in use
Current pager: stdout
Using outfile: ''
Using delimiter: ;
Server version: 5.7.-log MySQL Community Server (GPL)
Protocol version:
Connection: Localhost via UNIX socket
Server characterset: utf8
Db characterset: utf8
Client characterset: utf8
Conn. characterset: utf8
UNIX socket: /tmp/mysql3306.sock
Uptime: hours min sec Threads: Questions: Slow queries: Opens: Flush tables: Open tables: Queries per second avg: 0.003
-------------- (root@localhost mysql3306.sock)[(none)]>set names latin1;
Query OK, rows affected (0.00 sec) (root@localhost mysql3306.sock)[(none)]>\s
--------------
mysql Ver 14.14 Distrib 5.7., for linux-glibc2. (x86_64) using EditLine wrapper Connection id:
Current database:
Current user: root@localhost
SSL: Not in use
Current pager: stdout
Using outfile: ''
Using delimiter: ;
Server version: 5.7.-log MySQL Community Server (GPL)
Protocol version:
Connection: Localhost via UNIX socket
Server characterset: utf8
Db characterset: utf8
Client characterset: latin1
Conn. characterset: latin1
UNIX socket: /tmp/mysql3306.sock
Uptime: hours min sec Threads: Questions: Slow queries: Opens: Flush tables: Open tables: Queries per second avg: 0.003
-------------- (root@localhost mysql3306.sock)[(none)]>select @@character_set_client;
+------------------------+
| @@character_set_client |
+------------------------+
| latin1 |
+------------------------+
row in set (0.00 sec) (root@localhost mysql3306.sock)[(none)]>select @@character_set_connection;
+----------------------------+
| @@character_set_connection |
+----------------------------+
| latin1 |
+----------------------------+
row in set (0.00 sec) (root@localhost mysql3306.sock)[(none)]>select @@character_set_results;
+-------------------------+
| @@character_set_results |
+-------------------------+
| latin1 |
+-------------------------+
row in set (0.00 sec) (root@localhost mysql3306.sock)[(none)]>show variables like '%collation%';
+----------------------+-------------------+
| Variable_name | Value |
+----------------------+-------------------+
| collation_connection | latin1_swedish_ci |
| collation_database | utf8_general_ci |
| collation_server | utf8_general_ci |
+----------------------+-------------------+
rows in set (0.00 sec) //The influence of command "set names latin1" to character set is to change "character_set_client","character_set_connection","character_set_results" into latin1.
//The influence of command "set names latin1" to collation is to change "collation_connection" into latin1.
Case of change character set from utf8 to latin1 with "set character set ...;".
(root@localhost mysql3306.sock)[(none)]>\s
--------------
mysql Ver 14.14 Distrib 5.7., for linux-glibc2. (x86_64) using EditLine wrapper Connection id:
Current database:
Current user: root@localhost
SSL: Not in use
Current pager: stdout
Using outfile: ''
Using delimiter: ;
Server version: 5.7.-log MySQL Community Server (GPL)
Protocol version:
Connection: Localhost via UNIX socket
Server characterset: utf8
Db characterset: utf8
Client characterset: latin1
Conn. characterset: utf8
UNIX socket: /tmp/mysql3306.sock
Uptime: hours min sec Threads: Questions: Slow queries: Opens: Flush tables: Open tables: Queries per second avg: 0.004
-------------- (root@localhost mysql3306.sock)[(none)]>select @@character_set_client;
+------------------------+
| @@character_set_client |
+------------------------+
| latin1 |
+------------------------+
row in set (0.00 sec) (root@localhost mysql3306.sock)[(none)]>select @@character_set_connection;
+----------------------------+
| @@character_set_connection |
+----------------------------+
| utf8 |
+----------------------------+
row in set (0.00 sec) (root@localhost mysql3306.sock)[(none)]>select @@character_set_results;
+-------------------------+
| @@character_set_results |
+-------------------------+
| latin1 |
+-------------------------+
row in set (0.00 sec) (root@localhost mysql3306.sock)[(none)]>show variables like '%collation%';
+----------------------+-----------------+
| Variable_name | Value |
+----------------------+-----------------+
| collation_connection | utf8_general_ci |
| collation_database | utf8_general_ci |
| collation_server | utf8_general_ci |
+----------------------+-----------------+
rows in set (0.00 sec) //The two variables about "connection" was not altered this time.They were still utf8 relevant.
Case of change character set of server & database from utf8 to latin1.
(root@localhost mysql3306.sock)[(none)]>\s
--------------
mysql Ver 14.14 Distrib 5.7., for linux-glibc2. (x86_64) using EditLine wrapper Connection id:
Current database:
Current user: root@localhost
SSL: Not in use
Current pager: stdout
Using outfile: ''
Using delimiter: ;
Server version: 5.7.-log MySQL Community Server (GPL)
Protocol version:
Connection: Localhost via UNIX socket
Server characterset: utf8
Db characterset: utf8
Client characterset: utf8
Conn. characterset: utf8
UNIX socket: /tmp/mysql3306.sock
Uptime: hours min sec Threads: Questions: Slow queries: Opens: Flush tables: Open tables: Queries per second avg: 0.005
-------------- (root@localhost mysql3306.sock)[(none)]>set character_set_server=latin1;
Query OK, rows affected (0.00 sec) (root@localhost mysql3306.sock)[(none)]>set character_set_database=latin1;
Query OK, rows affected, warning (0.00 sec) (root@localhost mysql3306.sock)[(none)]>show warnings;
+---------+------+-------------------------------------------------------------------------------------------------+
| Level | Code | Message |
+---------+------+-------------------------------------------------------------------------------------------------+
| Warning | | Updating 'character_set_database' is deprecated. It will be made read-only in a future release. |
+---------+------+-------------------------------------------------------------------------------------------------+
row in set (0.00 sec) (root@localhost mysql3306.sock)[(none)]>\s
--------------
mysql Ver 14.14 Distrib 5.7., for linux-glibc2. (x86_64) using EditLine wrapper Connection id:
Current database:
Current user: root@localhost
SSL: Not in use
Current pager: stdout
Using outfile: ''
Using delimiter: ;
Server version: 5.7.-log MySQL Community Server (GPL)
Protocol version:
Connection: Localhost via UNIX socket
Server characterset: latin1
Db characterset: latin1
Client characterset: utf8
Conn. characterset: utf8
UNIX socket: /tmp/mysql3306.sock
Uptime: hours min sec Threads: Questions: Slow queries: Opens: Flush tables: Open tables: Queries per second avg: 0.005
-------------- //It shows that change "character_set_server" online is not supported in future release because of safety concern.
//Change character set of database may bring about risk of data loss if your client program using the supersetwhile database using subset.(eg. client->utf8mb4,database->utf8,will lost emoji data.)
Example of messy code.
(root@localhost mysql3306.sock)[zlm]>create table test_charset(
-> s1 char() character set latin1 not null,
-> s2 char() char set gbk,
-> s3 varchar() charset utf8,
-> s4 varchar()) character set=utf8mb4 engine=innodb;
Query OK, rows affected (0.01 sec) (root@localhost mysql3306.sock)[zlm]>show create table test_charset;
+--------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table |
+--------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| test_charset | CREATE TABLE `test_charset` (
`s1` char() CHARACTER SET latin1 NOT NULL,
`s2` char() CHARACTER SET gbk DEFAULT NULL,
`s3` varchar() CHARACTER SET utf8 DEFAULT NULL,
`s4` varchar() DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 |
+--------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
row in set (0.00 sec) (root@localhost mysql3306.sock)[zlm]>insert into test_charset values('ASCII','国标','万国','表情');
Query OK, row affected (0.00 sec) (root@localhost mysql3306.sock)[zlm]>select * from test_charset;
+-------+--------+--------+--------+
| s1 | s2 | s3 | s4 |
+-------+--------+--------+--------+
| ASCII | 国标 | 万国 | 表情 |
+-------+--------+--------+--------+
row in set (0.00 sec) (root@localhost mysql3306.sock)[zlm]>\s
--------------
mysql Ver 14.14 Distrib 5.7., for linux-glibc2. (x86_64) using EditLine wrapper Connection id:
Current database: zlm
Current user: root@localhost
SSL: Not in use
Current pager: stdout
Using outfile: ''
Using delimiter: ;
Server version: 5.7.-log MySQL Community Server (GPL)
Protocol version:
Connection: Localhost via UNIX socket
Server characterset: utf8
Db characterset: utf8
Client characterset: utf8
Conn. characterset: utf8
UNIX socket: /tmp/mysql3306.sock
Uptime: hours min sec Threads: Questions: Slow queries: Opens: Flush tables: Open tables: Queries per second avg: 0.006
-------------- (root@localhost mysql3306.sock)[zlm]>set names latin1;
Query OK, rows affected (0.00 sec) (root@localhost mysql3306.sock)[zlm]>\s
--------------
mysql Ver 14.14 Distrib 5.7., for linux-glibc2. (x86_64) using EditLine wrapper Connection id:
Current database: zlm
Current user: root@localhost
SSL: Not in use
Current pager: stdout
Using outfile: ''
Using delimiter: ;
Server version: 5.7.-log MySQL Community Server (GPL)
Protocol version:
Connection: Localhost via UNIX socket
Server characterset: utf8
Db characterset: utf8
Client characterset: latin1
Conn. characterset: latin1
UNIX socket: /tmp/mysql3306.sock
Uptime: hours min sec Threads: Questions: Slow queries: Opens: Flush tables: Open tables: Queries per second avg: 0.008
-------------- (root@localhost mysql3306.sock)[zlm]> (root@localhost mysql3306.sock)[zlm]>select * from test_charset;
+-------+------+------+------+
| s1 | s2 | s3 | s4 |
+-------+------+------+------+
| ASCII | ?? | ?? | ?? |
+-------+------+------+------+
row in set (0.00 sec) (root@localhost mysql3306.sock)[zlm]>set names gbk;
Query OK, rows affected (0.00 sec) (root@localhost mysql3306.sock)[zlm]>\s
--------------
mysql Ver 14.14 Distrib 5.7., for linux-glibc2. (x86_64) using EditLine wrapper Connection id:
Current database: zlm
Current user: root@localhost
SSL: Not in use
Current pager: stdout
Using outfile: ''
Using delimiter: ;
Server version: 5.7.-log MySQL Community Server (GPL)
Protocol version:
Connection: Localhost via UNIX socket
Server characterset: utf8
Db characterset: utf8
Client characterset: gbk
Conn. characterset: gbk
UNIX socket: /tmp/mysql3306.sock
Uptime: hours min sec Threads: Questions: Slow queries: Opens: Flush tables: Open tables: Queries per second avg: 0.006
-------------- (root@localhost mysql3306.sock)[zlm]>select * from test_charset;
+-------+------+------+------+
| s1 | s2 | s3 | s4 |
+-------+------+------+------+
| ASCII | ¹螠 | β¹ | ± |
+-------+------+------+------+
row in set (0.00 sec) (root@localhost mysql3306.sock)[zlm]>set names utf8mb4;
Query OK, rows affected (0.00 sec) (root@localhost mysql3306.sock)[zlm]>\s
--------------
mysql Ver 14.14 Distrib 5.7., for linux-glibc2. (x86_64) using EditLine wrapper Connection id:
Current database: zlm
Current user: root@localhost
SSL: Not in use
Current pager: stdout
Using outfile: ''
Using delimiter: ;
Server version: 5.7.-log MySQL Community Server (GPL)
Protocol version:
Connection: Localhost via UNIX socket
Server characterset: utf8
Db characterset: utf8
Client characterset: utf8mb4
Conn. characterset: utf8mb4
UNIX socket: /tmp/mysql3306.sock
Uptime: hours min sec Threads: Questions: Slow queries: Opens: Flush tables: Open tables: Queries per second avg: 0.006
-------------- (root@localhost mysql3306.sock)[zlm]>select * from test_charset;
+-------+--------+--------+--------+
| s1 | s2 | s3 | s4 |
+-------+--------+--------+--------+
| ASCII | 国标 | 万国 | 表情 |
+-------+--------+--------+--------+
row in set (0.00 sec) //MySQL support define character set on database,table even on a single column.
//Messy code will occur when "character_set_result" is subset of the value of character set which has been stored only if it turns back to the value equal or bigger than the stored value.
Example of losting data.
(root@localhost mysql3306.sock)[(none)]>\s
--------------
mysql Ver 14.14 Distrib 5.7., for linux-glibc2. (x86_64) using EditLine wrapper Connection id:
Current database:
Current user: root@localhost
SSL: Not in use
Current pager: stdout
Using outfile: ''
Using delimiter: ;
Server version: 5.7.-log MySQL Community Server (GPL)
Protocol version:
Connection: Localhost via UNIX socket
Server characterset: utf8
Db characterset: utf8
Client characterset: utf8
Conn. characterset: utf8
UNIX socket: /tmp/mysql3306.sock
Uptime: min sec Threads: Questions: Slow queries: Opens: Flush tables: Open tables: Queries per second avg: 0.219
-------------- (root@localhost mysql3306.sock)[(none)]>set @@character_set_server=latin1;
Query OK, rows affected (0.00 sec) (root@localhost mysql3306.sock)[(none)]>set @@character_set_database=latin1;
Query OK, rows affected, warning (0.01 sec) (root@localhost mysql3306.sock)[(none)]>set @@character_set_connection=latin1;
Query OK, rows affected (0.00 sec) (root@localhost mysql3306.sock)[(none)]>\s
--------------
mysql Ver 14.14 Distrib 5.7., for linux-glibc2. (x86_64) using EditLine wrapper Connection id:
Current database:
Current user: root@localhost
SSL: Not in use
Current pager: stdout
Using outfile: ''
Using delimiter: ;
Server version: 5.7.-log MySQL Community Server (GPL)
Protocol version:
Connection: Localhost via UNIX socket
Server characterset: latin1
Db characterset: latin1
Client characterset: utf8
Conn. characterset: latin1
UNIX socket: /tmp/mysql3306.sock
Uptime: min sec Threads: Questions: Slow queries: Opens: Flush tables: Open tables: Queries per second avg: 0.213
-------------- (root@localhost mysql3306.sock)[(none)]>insert into test_charset values('ASCII','国标','万国','表情');
ERROR (3D000): No database selected
(root@localhost mysql3306.sock)[(none)]>use zlm
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A Database changed
(root@localhost mysql3306.sock)[zlm]>insert into test_charset values('ASCII','国标','万国','表情');
Query OK, row affected, warnings (0.01 sec) (root@localhost mysql3306.sock)[zlm]>show warnings;
+---------+------+-----------------------------------------------------------+
| Level | Code | Message |
+---------+------+-----------------------------------------------------------+
| Warning | | Invalid utf8 character string: '\xE5\x9B\xBD\xE6\xA0\x87' |
| Warning | | Invalid utf8 character string: '\xE4\xB8\x87\xE5\x9B\xBD' |
| Warning | | Invalid utf8 character string: '\xE8\xA1\xA8\xE6\x83\x85' |
+---------+------+-----------------------------------------------------------+
rows in set (0.00 sec) (root@localhost mysql3306.sock)[zlm]>select @@character_set_results;
+-------------------------+
| @@character_set_results |
+-------------------------+
| utf8 |
+-------------------------+
row in set (0.00 sec) (root@localhost mysql3306.sock)[zlm]>select * from test_charset;
+-------+--------+--------+--------+
| s1 | s2 | s3 | s4 |
+-------+--------+--------+--------+
| ASCII | 国标 | 万国 | 表情 |
| ASCII | ?? | ?? | ?? |
+-------+--------+--------+--------+
rows in set (0.00 sec) (root@localhost mysql3306.sock)[zlm]>set @@character_set_results=latin1;
Query OK, rows affected (0.00 sec) (root@localhost mysql3306.sock)[zlm]>select @@character_set_results;
+-------------------------+
| @@character_set_results |
+-------------------------+
| latin1 |
+-------------------------+
row in set (0.00 sec) (root@localhost mysql3306.sock)[zlm]>select * from test_charset;
+-------+------+------+------+
| s1 | s2 | s3 | s4 |
+-------+------+------+------+
| ASCII | ?? | ?? | ?? |
| ASCII | ?? | ?? | ?? |
+-------+------+------+------+
rows in set (0.00 sec) //The data of first row has been correctly resored in database.
//The data of second row has lost the Chinese character data.
//The value of "character_set_result" only influence the screen output.
//There's a data loss risk while value of character set of client is superset of the one of database.
Summary
- MySQL character set is flexible and various,be more careful when modify data.
- The parameter "default_character_set" only affect original mysql client not for the other client tools.
- Make sure your character set of client is a subset but superset of the value of database when modifying data.Meanwhile it needs to be small than character set of connection to avoid data loss.
- It's recommended to set character set of database to a big set such as utf8 even utf8mb4 to be compatible with most characters of various languages.
浅谈MySQL字符集的更多相关文章
- 浅谈mysql主从复制的高可用解决方案
1.熟悉几个组件(部分摘自网络)1.1.drbd —— DRBD(Distributed Replicated Block Device),DRBD号称是 "网络 RAID" ...
- 浅谈mysql innodb缓存策略
浅谈mysql innodb缓存策略: The InnoDB Buffer Pool Innodb 持有一个存储区域叫做buffer pool是为了在内存中缓存数据和索引,知道innodb buffe ...
- 浅谈mysql配置优化和sql语句优化【转】
做优化,我在这里引用淘宝系统分析师蒋江伟的一句话:只有勇于承担,才能让人有勇气,有承担自己的错误的勇气.有承担错误的勇气,就有去做事得勇气.无论做什么事,只要是对的,就要去做,勇敢去做.出了错误,承担 ...
- 浅谈MySQL中优化sql语句查询常用的30种方法 - 转载
浅谈MySQL中优化sql语句查询常用的30种方法 1.对查询进行优化,应尽量避免全表扫描,首先应考虑在 where 及 order by 涉及的列上建立索引. 2.应尽量避免在 where 子句中使 ...
- 浅谈Mysql共享锁、排他锁、悲观锁、乐观锁及其使用场景
浅谈Mysql共享锁.排他锁.悲观锁.乐观锁及其使用场景 Mysql共享锁.排他锁.悲观锁.乐观锁及其使用场景 一.相关名词 |--表级锁(锁定整个表) |--页级锁(锁定一页) |--行级锁(锁 ...
- 浅谈MySQL存储引擎-InnoDB&MyISAM
存储引擎在MySQL的逻辑架构中位于第三层,负责MySQL中的数据的存储和提取.MySQL存储引擎有很多,不同的存储引擎保存数据和索引的方式是不同的.每一种存储引擎都有它的优势和劣势,本文只讨论最常见 ...
- 重新学习MySQL数据库6：浅谈MySQL的中事务与锁
『浅入深出』MySQL 中事务的实现 在关系型数据库中,事务的重要性不言而喻,只要对数据库稍有了解的人都知道事务具有 ACID 四个基本属性,而我们不知道的可能就是数据库是如何实现这四个属性的:在这篇 ...
- （转）运维角度浅谈MySQL数据库优化
转自:http://lizhenliang.blog.51cto.com/7876557/1657465 一个成熟的数据库架构并不是一开始设计就具备高可用.高伸缩等特性的,它是随着用户量的增加,基础架 ...
- 运维角度浅谈MySQL数据库优化(转)
一个成熟的数据库架构并不是一开始设计就具备高可用.高伸缩等特性的,它是随着用户量的增加,基础架构才逐渐完善.这篇博文主要谈MySQL数据库发展周期中所面临的问题及优化方案,暂且抛开前端应用不说,大致分 ...
随机推荐
- 牛客网Java刷题知识点之内存的划分（寄存器、本地方法区、方法区、栈内存和堆内存）
不多说,直接上干货! 其中 1)程序计数器:用于指示当前线程所执行的字节码执行到了第几行,可以理解为当前线程的行号指示器.每个计数器志勇赖记录一个线程的行号,所以它是线程私有的. ...
- 07-spring之三大框架的整合
1 三大框架整合理论 2 导包(42个) 1 hibernate 1 hibernate/lib/required 2 hibernate/lib/jpa | java persist api jav ...
- Echarts学习笔记
1.Ecahrts使用首先需要引用js文件 Echarts.js 然后定义一个带id的容器(div就可以) 然后就可以初始化echarts了 ↓这是柱形图 <h2 class="con ...
- Java-Excel写与读
很多时候,一个软件应用程序需要生成Microsoft Excel文件格式的报告.有时,一个应用程序甚至希望将Excel文件作为输入数据.例如,一个公司开发的应用程序将财务部门需要所有输出生成自己的Ex ...
- 权限修饰符（public、protected、default、private）权限验证
一.测试方法 在authorityTest包中建类AuthorityValidate package authorityTest; public class AuthorityValidate { p ...
- aliyun maven repository
<mirrors> <mirror> <id>alimaven</id> <name>aliyun maven</name> & ...
- Android基础Activity篇——Intent向下一个活动传递数据
1.向下一个活动传递数据 String data ="bilibilbilbilbili"; Intent intent1=new Intent(this,secondActivi ...
- OpenCV-3.4.2基于Qt-5.10.1的编译
OpenCV-3.4.2基于Qt-5.10.1的编译 由于本人在使用CMake和MinGW编译OpenCV是遇到了很多问题,在这里记录下来.至于所需软件的安装和相应环境变量的设置,网上有很多详细的教程 ...
- jshint-eclipse: JavaScript Code Quality Plugin for Eclipse
https://blog.oio.de/2012/03/26/jshint-eclipse-javascript-code-quality-plugin-for-eclipse/ techscou ...
- Cmake 01
1. sdsf(single direction single file) 1.1 The directory tree /* ./template | +--- build | +---main. ...