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MySQL同步故障：" Slave_SQL_Running:No" 两种解决办法

liangcmwn — Tue, 16 Aug 2011 01:31:00 GMT

进入slave服务器，运行：

mysql> show slave status\G

         .......
             Relay_Log_File: localhost-relay-bin.000535
              Relay_Log_Pos: 21795072
      Relay_Master_Log_File: localhost-bin.000094
           Slave_IO_Running: Yes
          Slave_SQL_Running: No
            Replicate_Do_DB:
        Replicate_Ignore_DB:
      ......

解决办法一、

Slave_SQL_Running: No
1.程序可能在slave上进行了写操作

2.也可能是slave机器重起后，事务回滚造成的.

一般是事务回滚造成的：
解决办法：
mysql> slave stop;
mysql> set GLOBAL SQL_SLAVE_SKIP_COUNTER=1;
mysql> slave start;

解决办法二、

首先停掉Slave服务：slave stop
到主服务器上查看主机状态：
记录File和Position对应的值

进入master

然后到slave服务器上执行手动同步：
mysql> change master to > master_host='master_ip', > master_user='user', > master_password='pwd', > master_port=3306, > master_log_file=localhost-bin.000094', > master_log_pos=33622483 ; 1 row in set (0.00 sec) mysql> slave start; 1 row in set (0.00 sec)

mysql> show slave status\G
*************************** 1. row ***************************
........
            Master_Log_File: localhost-bin.000094
        Read_Master_Log_Pos: 33768775
             Relay_Log_File: localhost-relay-bin.000537
              Relay_Log_Pos: 1094034
      Relay_Master_Log_File: localhost-bin.000094
           Slave_IO_Running: Yes
          Slave_SQL_Running: Yes
            Replicate_Do_DB:

手动同步需要停止master的写操作！

liangcmwn 2011-08-16 09:31 发表评论

MySQL InnoDB存储引擎的事务隔离级别

liangcmwn — Tue, 16 Aug 2011 01:15:00 GMT

我们知道，在关系数据库标准中有四个事务隔离级别：

未提交读(Read Uncommitted)：允许脏读，也就是可能读取到其他会话中未提交事务修改的数据
提交读(Read Committed)：只能读取到已经提交的数据。Oracle等多数数据库默认都是该级别
可重复读(Repeated Read)：可重复读。在同一个事务内的查询都是事务开始时刻一致的，InnoDB默认级别。在SQL标准中，该隔离级别消除了不可重复读，但是还存在幻象读
串行读(Serializable)：完全串行化的读，每次读都需要获得表级共享锁，读写相互都会阻塞

查看InnoDB系统级别的事务隔离级别：

mysql> SELECT @@global.tx_isolation;
+-----------------------+
| @@global.tx_isolation |
+-----------------------+
| REPEATABLE-READ |
+-----------------------+
1 row in set (0.00 sec)

查看InnoDB会话级别的事务隔离级别：

mysql> SELECT @@tx_isolation;
+-----------------+
| @@tx_isolation |
+-----------------+
| REPEATABLE-READ |
+-----------------+
1 row in set (0.00 sec)

修改事务隔离级别：

mysql> set global transaction isolation level read committed;
Query OK, 0 rows affected (0.00 sec)

mysql> set session transaction isolation level read committed;
Query OK, 0 rows affected (0.00 sec)

InnoDB的可重复读隔离级别和其他数据库的可重复读是有区别的，不会造成幻象读（phantom read），所谓幻象读，就是同一个事务内，多次select，可以读取到其他session insert并已经commit的数据。下面是一个小的测试，证明InnoDB的可重复读隔离级别不会造成幻象读。测试涉及两个session，分别为session 1和session 2，隔离级别都是repeateable read，关闭autocommit

mysql> select @@tx_isolation;
+-----------------+
| @@tx_isolation |
+-----------------+
| REPEATABLE-READ |
+-----------------+
1 row in set (0.00 sec)

mysql> set autocommit=off;
Query OK, 0 rows affected (0.00 sec)

session 1 创建表并插入测试数据

mysql> create table test(i int) engine=innodb;
Query OK, 0 rows affected (0.00 sec)

mysql> insert into test values(1);
Query OK, 1 row affected (0.00 sec)

session 2 查询，没有数据，正常，session1没有提交，不允许脏读

mysql> select * from test;
Empty set (0.00 sec)

session 1 提交事务

mysql> commit;
Query OK, 0 rows affected (0.00 sec)

session 2 查询，还是没有数据，没有产生幻象读

mysql> select * from test;
Empty set (0.00 sec)

以上试验版本：

mysql> select version();
+-------------------------+
| version() |
+-------------------------+
| 5.0.37-community-nt-log |
+-------------------------+
1 row in set (0.00 sec)

--EOF--

作者：江枫| 【转载时请务必以超链接形式标明文章原始出处和作者信息及本声明】
地址：http://rdc.taobao.com/blog/dba/html/91_mysql_innodb_transaction_isolation_level.html

liangcmwn 2011-08-16 09:15 发表评论

Mysql常用操作

liangcmwn — Mon, 15 Aug 2011 08:50:00 GMT

查看MySQL的当前存储引擎

一般情况下，mysql会默认提供多种存储引擎,你可以通过下面的查看:

看你的mysql现在已提供什么存储引擎:
mysql> show engines;

看你的mysql当前默认的存储引擎:
mysql> show variables like '%storage_engine%';

你要看某个表用了什么引擎(在显示结果里参数engine后面的就表示该表当前用的存储引擎):
mysql> show create table 表名;

MySQL 乱码的根源是的 MySQL 字符集设置不当的问题，本文汇总了有关查看 MySQL 字符集的命令。包括查看 MySQL 数据库服务器字符集、查看 MySQL 数据库字符集，以及数据表和字段的字符集、当前安装的 MySQL 所支持的字符集等。

一、查看 MySQL 数据库服务器和数据库字符集。

mysql> show variables like '%char%';
+--------------------------+-------------------------------------+------
| Variable_name            | Value                               |......
+--------------------------+-------------------------------------+------
| character_set_client     | utf8                                |......   -- 客户端字符集
| character_set_connection | utf8                                |......
| character_set_database   | utf8                                |......   -- 数据库字符集
| character_set_filesystem | binary                              |......
| character_set_results    | utf8                                |......
| character_set_server     | utf8                                |......   -- 服务器字符集
| character_set_system     | utf8                                |......
| character_sets_dir       | D:\MySQL Server 5.0\share\charsets\ |......
+--------------------------+-------------------------------------+------

二、查看 MySQL 数据表（table）的字符集。

mysql> show table status from sqlstudy_db like '%countries%';
+-----------+--------+---------+------------+------+-----------------+------
| Name      | Engine | Version | Row_format | Rows | Collation       |......
+-----------+--------+---------+------------+------+-----------------+------
| countries | InnoDB |      10 | Compact    |   11 | utf8_general_ci |......
+-----------+--------+---------+------------+------+-----------------+------

三、查看 MySQL 数据列（column）的字符集。

mysql> show full columns from countries;
+----------------------+-------------+-----------------+--------
| Field                | Type        | Collation       | .......
+----------------------+-------------+-----------------+--------
| countries_id         | int(11)     | NULL            | .......
| countries_name       | varchar(64) | utf8_general_ci | .......
| countries_iso_code_2 | char(2)     | utf8_general_ci | .......
| countries_iso_code_3 | char(3)     | utf8_general_ci | .......
| address_format_id    | int(11)     | NULL            | .......
+----------------------+-------------+-----------------+--------

四、查看当前安装的 MySQL 所支持的字符集。

mysql> show charset;
mysql> show char 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 |
| cp1251   | Windows Cyrillic            | cp1251_general_ci   |      1 |
| cp1256   | Windows Arabic              | cp1256_general_ci   |      1 |
| cp1257   | Windows Baltic              | cp1257_general_ci   |      1 |
| 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 |
+----------+-----------------------------+---------------------+--------+

以上查看 MySQL 字符集命令，适用于 Windows & Linux。

liangcmwn 2011-08-15 16:50 发表评论

mysql中limit用法

liangcmwn — Wed, 27 Jul 2011 09:10:00 GMT

使用查询语句的时候，经常要返回前几条或者中间某几行数据，这个时候怎么办呢？不用担心，mysql已经为我们提供了这样一个功能。

SELECT * FROM table LIMIT [offset,] rows | rows OFFSET offset

LIMIT 子句可以被用于强制 SELECT 语句返回指定的记录数。LIMIT 接受一个或两个数字参数。参数必须是一个整数常量。如果给定两个参数，第一个参数指定第一个返回记录行的偏移量，第二个参数指定返回记录行的最大数目。初始记录行的偏移量是 0(而不是 1)：为了与 PostgreSQL 兼容，MySQL 也支持句法： LIMIT # OFFSET #。

mysql> SELECT * FROM table LIMIT 5,10; // 检索记录行 6-15

//为了检索从某一个偏移量到记录集的结束所有的记录行，可以指定第二个参数为 -1：
mysql> SELECT * FROM table LIMIT 95,-1; // 检索记录行 96-last.

//如果只给定一个参数，它表示返回最大的记录行数目：
mysql> SELECT * FROM table LIMIT 5; //检索前 5 个记录行

//换句话说，LIMIT n 等价于 LIMIT 0,n。

实例：

mysql> use sppeivan;
Database changed
mysql> select * from employee; // 返回所有结果
+------------+------------+--------+-------------+
| username   | password   | gender | cellphone   |
+------------+------------+--------+-------------+
| ewrew      | erewr      | MAN    | 13618889076 |
| ewrwerw32r | 324324     | MAN    | 13618889076 |
| grrrrr     | r44343     | WOMAN | 13618889076 |
| pansong    | erewrwe    | MAN    | 13618889076 |
| ret43t43t | 43t43      | MAN    | 13618889076 |
| ret44t4    | r4tgr      | WOMAN | 13618889076 |
| tttt       | 4et        | WOMAN | 13618889076 |
| wr34r      | retre      | MAN    | 13618889076 |
| xxx     | safe       | MAN    | 13618889076 |
| hhh       | ewrwer     | MAN    | 13618889076 |
| hg       | 6574326543 | MAN    | 13618889076 |
| ps       | ewrwe      | MAN    | 13618889076 |
| zhu       | werew      | MAN    | 13618889076 |
+------------+------------+--------+-------------+
13 rows in set (0.01 sec)

mysql> select * from employee limit 3 7;
ERROR 1064 (42000): You have an error in your SQL syntax
corresponds to your MySQL server version for the right s
line 1
mysql> select * from employee limit 3, 7; // 返回4-11行
+-----------+----------+--------+-------------+
| username | password | gender | cellphone   |
+-----------+----------+--------+-------------+
| pansong   | erewrwe | MAN    | 13618889076 |
| ret43t43t | 43t43    | MAN    | 13618889076 |
| ret44t4   | r4tgr    | WOMAN | 13618889076 |
| tttt      | 4et      | WOMAN | 13618889076 |
| wr34r     | retre    | MAN    | 13618889076 |
| xxx     | safe     | MAN    | 13618889076 |
| hhh      | ewrwer   | MAN    | 13618889076 |
+-----------+----------+--------+-------------+
7 rows in set (0.00 sec)

mysql> select * from employee limit 3,-1; // 错误语法
ERROR 1064 (42000): You have an error in your SQL syntax
corresponds to your MySQL server version for the right s
t line 1

mysql> select * from employee limit 3; // 返回前3行

+------------+----------+--------+-------------+
| username   | password | gender | cellphone   |
+------------+----------+--------+-------------+
| ewrew      | erewr    | MAN    | 13618889076 |
| ewrwerw32r | 324324   | MAN    | 13618889076 |
| grrrrr     | r44343   | WOMAN | 13618889076 |
+------------+----------+--------+-------------+
3 rows in set (0.00 sec)

mysql> select * from employee limit 10; // 返回前10行

+------------+----------+--------+-------------+
| username   | password | gender | cellphone   |
+------------+----------+--------+-------------+
| ewrew      | erewr    | MAN    | 13618889076 |
| ewrwerw32r | 324324   | MAN    | 13618889076 |
| grrrrr     | r44343   | WOMAN | 13618889076 |
| pansong    | erewrwe | MAN    | 13618889076 |
| ret43t43t | 43t43    | MAN    | 13618889076 |
| ret44t4    | r4tgr    | WOMAN | 13618889076 |
| tttt       | 4et      | WOMAN | 13618889076 |
| wr34r      | retre    | MAN    | 13618889076 |
| xxx     | safe     | MAN    | 13811588469 |
| hhh       | ewrwer   | MAN    | 13618889076 |
+------------+----------+--------+-------------+
10 rows in set (0.00 sec)

liangcmwn 2011-07-27 17:10 发表评论