查看设置系统信息
1. 储存引擎相关
## 1 查看当前支持的储存引擎
MariaDB [(none)]> show engines;
+--------------------+---------+----------------------------------------------------------------------------+--------------+------+------------+
| Engine | Support | Comment | Transactions | XA | Savepoints |
+--------------------+---------+----------------------------------------------------------------------------+--------------+------+------------+
| CSV | YES | CSV storage engine | NO | NO | NO |
| MRG_MYISAM | YES | Collection of identical MyISAM tables | NO | NO | NO |
| MEMORY | YES | Hash based, stored in memory, useful for temporary tables | NO | NO | NO |
| BLACKHOLE | YES | /dev/null storage engine (anything you write to it disappears) | NO | NO | NO |
| MyISAM | YES | MyISAM storage engine | NO | NO | NO |
| InnoDB | DEFAULT | Percona-XtraDB, Supports transactions, row-level locking, and foreign keys | YES | YES | YES |
| ARCHIVE | YES | Archive storage engine | NO | NO | NO |
| FEDERATED | YES | FederatedX pluggable storage engine | YES | NO | YES |
| PERFORMANCE_SCHEMA | YES | Performance Schema | NO | NO | NO |
| Aria | YES | Crash-safe tables with MyISAM heritage | NO | NO | NO |
+--------------------+---------+----------------------------------------------------------------------------+--------------+------+------------+
10 rows in set (0.00 sec)
## 2 查看默认的储存引擎
MariaDB [(none)]> show variables like '%engine%';
+---------------------------+--------+
| Variable_name | Value |
+---------------------------+--------+
| default_storage_engine | InnoDB |
| engine_condition_pushdown | OFF |
| storage_engine | InnoDB |
+---------------------------+--------+
## 3 查看表的储存引擎
MariaDB [test]> show create table dept;
+-------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table |
+-------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| dept | CREATE TABLE `dept` (
`deptno` int(11) NOT NULL,
`dname` varchar(14) DEFAULT NULL,
`loc` varchar(13) DEFAULT NULL,
PRIMARY KEY (`deptno`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1 |
+-------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)
2. 字符集
MariaDB [test]> show character set;
+----------+-----------------------------+---------------------+--------+
| Charset | Description | Default collation | Maxlen |
+----------+-----------------------------+---------------------+--------+
| big5 | Big5 Traditional Chinese | big5_chinese_ci | 2 |
| dec8 | DEC West European | dec8_swedish_ci | 1 |
| cp850 | DOS West European | cp850_general_ci | 1 |
| hp8 | HP West European | hp8_english_ci | 1 |
| koi8r | KOI8-R Relcom Russian | koi8r_general_ci | 1 |
| latin1 | cp1252 West European | latin1_swedish_ci | 1 |
| latin2 | ISO 8859-2 Central European | latin2_general_ci | 1 |
| swe7 | 7bit Swedish | swe7_swedish_ci | 1 |
| ascii | US ASCII | ascii_general_ci | 1 |
| ujis | EUC-JP Japanese | ujis_japanese_ci | 3 |
| sjis | Shift-JIS Japanese | sjis_japanese_ci | 2 |
| hebrew | ISO 8859-8 Hebrew | hebrew_general_ci | 1 |
| tis620 | TIS620 Thai | tis620_thai_ci | 1 |
| euckr | EUC-KR Korean | euckr_korean_ci | 2 |
| koi8u | KOI8-U Ukrainian | koi8u_general_ci | 1 |
| gb2312 | GB2312 Simplified Chinese | gb2312_chinese_ci | 2 |
| greek | ISO 8859-7 Greek | greek_general_ci | 1 |
| cp1250 | Windows Central European | cp1250_general_ci | 1 |
| gbk | GBK Simplified Chinese | gbk_chinese_ci | 2 |
| latin5 | ISO 8859-9 Turkish | latin5_turkish_ci | 1 |
| armscii8 | ARMSCII-8 Armenian | armscii8_general_ci | 1 |
| utf8 | UTF-8 Unicode | utf8_general_ci | 3 |
| ucs2 | UCS-2 Unicode | ucs2_general_ci | 2 |
| cp866 | DOS Russian | cp866_general_ci | 1 |
| keybcs2 | DOS Kamenicky Czech-Slovak | keybcs2_general_ci | 1 |
| macce | Mac Central European | macce_general_ci | 1 |
| macroman | Mac West European | macroman_general_ci | 1 |
| cp852 | DOS Central European | cp852_general_ci | 1 |
| latin7 | ISO 8859-13 Baltic | latin7_general_ci | 1 |
| utf8mb4 | UTF-8 Unicode | utf8mb4_general_ci | 4 |
| cp1251 | Windows Cyrillic | cp1251_general_ci | 1 |
| utf16 | UTF-16 Unicode | utf16_general_ci | 4 |
| cp1256 | Windows Arabic | cp1256_general_ci | 1 |
| cp1257 | Windows Baltic | cp1257_general_ci | 1 |
| utf32 | UTF-32 Unicode | utf32_general_ci | 4 |
| binary | Binary pseudo charset | binary | 1 |
| geostd8 | GEOSTD8 Georgian | geostd8_general_ci | 1 |
| cp932 | SJIS for Windows Japanese | cp932_japanese_ci | 2 |
| eucjpms | UJIS for Windows Japanese | eucjpms_japanese_ci | 3 |
+----------+-----------------------------+---------------------+--------+
39 rows in set (0.02 sec)
MariaDB [test]> select * from information_schema.character_sets;
+--------------------+----------------------+-----------------------------+--------+
| CHARACTER_SET_NAME | DEFAULT_COLLATE_NAME | DESCRIPTION | MAXLEN |
+--------------------+----------------------+-----------------------------+--------+
| big5 | big5_chinese_ci | Big5 Traditional Chinese | 2 |
| dec8 | dec8_swedish_ci | DEC West European | 1 |
| cp850 | cp850_general_ci | DOS West European | 1 |
| hp8 | hp8_english_ci | HP West European | 1 |
| koi8r | koi8r_general_ci | KOI8-R Relcom Russian | 1 |
| latin1 | latin1_swedish_ci | cp1252 West European | 1 |
| latin2 | latin2_general_ci | ISO 8859-2 Central European | 1 |
| swe7 | swe7_swedish_ci | 7bit Swedish | 1 |
| ascii | ascii_general_ci | US ASCII | 1 |
| ujis | ujis_japanese_ci | EUC-JP Japanese | 3 |
| sjis | sjis_japanese_ci | Shift-JIS Japanese | 2 |
| hebrew | hebrew_general_ci | ISO 8859-8 Hebrew | 1 |
| tis620 | tis620_thai_ci | TIS620 Thai | 1 |
| euckr | euckr_korean_ci | EUC-KR Korean | 2 |
| koi8u | koi8u_general_ci | KOI8-U Ukrainian | 1 |
| gb2312 | gb2312_chinese_ci | GB2312 Simplified Chinese | 2 |
| greek | greek_general_ci | ISO 8859-7 Greek | 1 |
| cp1250 | cp1250_general_ci | Windows Central European | 1 |
| gbk | gbk_chinese_ci | GBK Simplified Chinese | 2 |
| latin5 | latin5_turkish_ci | ISO 8859-9 Turkish | 1 |
| armscii8 | armscii8_general_ci | ARMSCII-8 Armenian | 1 |
| utf8 | utf8_general_ci | UTF-8 Unicode | 3 |
| ucs2 | ucs2_general_ci | UCS-2 Unicode | 2 |
| cp866 | cp866_general_ci | DOS Russian | 1 |
| keybcs2 | keybcs2_general_ci | DOS Kamenicky Czech-Slovak | 1 |
| macce | macce_general_ci | Mac Central European | 1 |
| macroman | macroman_general_ci | Mac West European | 1 |
| cp852 | cp852_general_ci | DOS Central European | 1 |
| latin7 | latin7_general_ci | ISO 8859-13 Baltic | 1 |
| utf8mb4 | utf8mb4_general_ci | UTF-8 Unicode | 4 |
| cp1251 | cp1251_general_ci | Windows Cyrillic | 1 |
| utf16 | utf16_general_ci | UTF-16 Unicode | 4 |
| cp1256 | cp1256_general_ci | Windows Arabic | 1 |
| cp1257 | cp1257_general_ci | Windows Baltic | 1 |
| utf32 | utf32_general_ci | UTF-32 Unicode | 4 |
| binary | binary | Binary pseudo charset | 1 |
| geostd8 | geostd8_general_ci | GEOSTD8 Georgian | 1 |
| cp932 | cp932_japanese_ci | SJIS for Windows Japanese | 2 |
| eucjpms | eucjpms_japanese_ci | UJIS for Windows Japanese | 3 |
+--------------------+----------------------+-----------------------------+--------+
39 rows in set (0.00 sec)
## 查看字符集
1. 服务器级别的字符集可以在配置文件中永久修改.
2. 数据库级别的字符集默认是继承服务器的字符集
3. 表的字符集会继承数据级别的字符集
3. 客户端,连接,返回结果集的字符集需要单独设置
4. character_set_client表明client发送给server用的是什么编码方式
5. character_set_connection表明传输的编码方式
6. character_set_results表明服务器返回出来的编码方式
eg: sql="select * from test;" , 这个就是client编码,然后转换到connection的编码,发送到服务器上,服务器解码获取sql语句.服务器出来的数据会使用results编码方式编码,然后又是connection编码,我们读取数据即可.
MariaDB [test]> show variables like 'char%';
+--------------------------+----------------------------+
| Variable_name | Value |
+--------------------------+----------------------------+
| character_set_client | utf8 |
| character_set_connection | utf8 |
| character_set_database | latin1 |
| character_set_filesystem | binary |
| character_set_results | utf8 |
| character_set_server | latin1 |
| character_set_system | utf8 |
| character_sets_dir | /usr/share/mysql/charsets/ |
+--------------------------+----------------------------+
8 rows in set (0.00 sec) 3. 隔离级别
1. 查看当前隔离级别
MariaDB [test]> show variables like '%isolation%';
+---------------+-----------------+
| Variable_name | Value |
+---------------+-----------------+
| tx_isolation | REPEATABLE-READ |
+---------------+-----------------+
1 row in set (0.00 sec)
MariaDB [test]> select @@tx_isolation;
+-----------------+
| @@tx_isolation |
+-----------------+
| REPEATABLE-READ |
+-----------------+
1 row in set (0.00 sec)
MariaDB [test]> help isolation;
Name: 'ISOLATION'
Description:
Syntax:
SET [GLOBAL | SESSION] TRANSACTION ISOLATION LEVEL
{
REPEATABLE READ
| READ COMMITTED
| READ UNCOMMITTED
| SERIALIZABLE
}2. 事务并行问题
- 脏读:读取到未提交数据
- 不可重复读:在同一个事务中执行相同的查询语句,获取的结果不一致，
同一条记录数据不一致 - 幻读: 保证在同一个事务中看到的数据是一样的.另一个数据提交了数据,然后本事务更新数据,就会看到另一个事务提交的数据.，
记录数量不一致
1. 读未提交级别
MariaDB [test]> set tx_isolation='read-uncommitted';
Query OK, 0 rows affected (0.00 sec)
MariaDB [test]> select @@tx_isolation;
+------------------+
| @@tx_isolation |
+------------------+
| READ-UNCOMMITTED |
+------------------+
1 row in set (0.00 sec)
## 事务A
###步骤1:开启事务
###步骤2:查看tx表的数据
MariaDB [test]> start transaction;
Query OK, 0 rows affected (0.00 sec)
MariaDB [test]> select * from tx;
+------+------+
| id | num |
+------+------+
| 1 | 1 |
| 2 | 2 |
| 3 | 3 |
+------+------+
3 rows in set (0.00 sec)
## 事务B
###步骤3:开启另一个终端,开启事务
###步骤4:更新tx表的数据
MariaDB [test]> update tx set num=10 where id=1;
Query OK, 1 row affected (0.00 sec)
Rows matched: 1 Changed: 1 Warnings: 0
MariaDB [test]> select * from tx;
+------+------+
| id | num |
+------+------+
| 1 | 10 |
| 2 | 2 |
| 3 | 3 |
+------+------+
3 rows in set (0.00 sec)
## 事务A
步骤5:查看tx表的数据
MariaDB [test]> select * from tx;
+------+------+
| id | num |
+------+------+
| 1 | 10 |
| 2 | 2 |
| 3 | 3 |
+------+------+
3 rows in set (0.00 sec)
总结: 从上面的结果可以看出,事务B更新了数据,但是没有提交的情况下,事务A就可以查看更新的数据,这就出现了脏读的情况
2. 读已提交级别
1. 设置隔离级别
MariaDB [test]> set tx_isolation='read-committed';
Query OK, 0 rows affected (0.00 sec)
MariaDB [test]> select @@tx_isolation;
+----------------+
| @@tx_isolation |
+----------------+
| READ-COMMITTED |
+----------------+
1 row in set (0.00 sec)
2. 操作
## 事务A
步骤1: 开启事务,查看tx表数据
MariaDB [test]> start transaction;
Query OK, 0 rows affected (0.00 sec)
MariaDB [test]> select * from tx;
+------+------+
| id | num |
+------+------+
| 1 | 1 |
| 2 | 2 |
| 3 | 3 |
+------+------+
3 rows in set (0.00 sec)
## 事务B
步骤2: 开启事务
步骤3:更新数据
步骤4:提交数据
MariaDB [test]> start transaction;
Query OK, 0 rows affected (0.00 sec)
MariaDB [test]> update tx set num=100 where id=1;
Query OK, 1 row affected (0.00 sec)
Rows matched: 1 Changed: 1 Warnings: 0
MariaDB [test]> commit;
Query OK, 0 rows affected (0.00 sec)
## 事务A
步骤5: 查看tx表的数据
MariaDB [test]> select * from tx;
+------+------+
| id | num |
+------+------+
| 1 | 100 |
| 2 | 2 |
| 3 | 3 |
+------+------+
3 rows in set (0.00 sec)3总结
读已提交隔离级别:事务A和事务B同时开启,事务B更改数据并提交,事务A在去查看的时候,已经可以看到更改的数据,出现了不可重复读的问题
3. 可重复读隔离级别
1. 设置隔离级别
MariaDB [test]> set tx_isolation='repeatable-read';
Query OK, 0 rows affected (0.00 sec)
MariaDB [test]> select @@tx_isolation;
+-----------------+
| @@tx_isolation |
+-----------------+
| REPEATABLE-READ |
+-----------------+
1 row in set (0.00 sec)
2. 操作
## 事务A
步骤1: 开启事务,查看tx表数据
MariaDB [test]> start transaction;
Query OK, 0 rows affected (0.00 sec)
MariaDB [test]> select * from tx;
+------+------+
| id | num |
+------+------+
| 1 | 1 |
| 2 | 2 |
| 3 | 3 |
+------+------+
3 rows in set (0.00 sec)
## 事务B
步骤2: 开启事务B
步骤3: 更新数据,提交
MariaDB [test]> start transaction;
Query OK, 0 rows affected (0.00 sec)
MariaDB [test]> update tx set num=100 where id = 1;
Query OK, 1 row affected (0.01 sec)
Rows matched: 1 Changed: 1 Warnings: 0
MariaDB [test]> select * from tx;
+------+------+
| id | num |
+------+------+
| 1 | 100 |
| 2 | 2 |
| 3 | 3 |
+------+------+
3 rows in set (0.00 sec)
MariaDB [test]> commit;
Query OK, 0 rows affected (0.01 sec)
MariaDB [test]> select * from tx;
+------+------+
| id | num |
+------+------+
| 1 | 100 |
| 2 | 2 |
| 3 | 3 |
+------+------+
3 rows in set (0.00 sec)
## 事务A
步骤4: 查看tx表的数据(看不到事务B已提交的数据)
MariaDB [test]> select * from tx;
+------+------+
| id | num |
+------+------+
| 1 | 1 |
| 2 | 2 |
| 3 | 3 |
+------+------+
3 rows in set (0.01 sec)
MariaDB [test]> insert into tx values(4,4);
Query OK, 1 row affected (0.01 sec)
## 这里本是可以看到事务B更新的数据,但是mysql的多版本控制,现在看到的时候tx的历史版本数据(快照)
MariaDB [test]> select * from tx;
+------+------+
| id | num |
+------+------+
| 1 | 1 |
| 2 | 2 |
| 3 | 3 |
| 4 | 4 |
+------+------+
4 rows in set (0.00 sec)
3总结
因为innodb存储引擎是有mvcc多版本控制,所以看不到最后insert数据的时候,本是可以看到事务B更新的数据,所以没有出现幻读现象
4 串行化隔离级别
1. 设置隔离级别
MariaDB [test]> set tx_isolation='serializable';
Query OK, 0 rows affected (0.00 sec)
MariaDB [test]> select @@tx_isolation;
+----------------+
| @@tx_isolation |
+----------------+
| SERIALIZABLE |
+----------------+
1 row in set (0.00 sec)2. 操作
## 事务A
MariaDB [test]> insert into tx values (6,6);
Query OK, 1 row affected (0.00 sec)
## 事务B
`因为事务之间是串行化操作的`
MariaDB [test]> insert into tx values(5,5);
ERROR 1205 (HY000): Lock wait timeout exceeded; try restarting transaction
## 事务A提交