bitsCN.com author:skate
time:2012/06/25
ERROR 126 (HY000): Incorrect key file for table '/tmp/#sql_1d87_0.MYI'; try to repair it
案例:
mysql> insert into t1 select * from t1;
^[[AQuery OK, 24576 rows affected (0.44 sec)
Records: 24576 Duplicates: 0 Warnings: 0
mysql> insert into t1 select * from t1;
Query OK, 49152 rows affected (1.90 sec)
Records: 49152 Duplicates: 0 Warnings: 0
mysql> insert into t1 select * from t1;
ERROR 126 (HY000): Incorrect key file for table '/tmp/#sql_1d87_0.MYI'; try to repair it
从上面的情况看,好似空间的问题,因为前几次insert都成功了,查看磁盘空间如下:
[root@localhost ~]# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/VolGroup00-LogVol00
5.3G 5.0G 50M 100% /
/dev/sda1 99M 12M 83M 13% /boot
tmpfs 125M 0 125M 0% /dev/shm
/dev/sdb1 7.7G 183M 7.2G 3% /data
在查看mysql数据目录情况
mysql> show variables like '%dir%';
+-----------------------------------------+------------------------------------+
| Variable_name | Value |
+-----------------------------------------+------------------------------------+
| basedir | /usr/local/mysql |
| binlog_direct_non_transactional_updates | OFF |
| character_sets_dir | /usr/local/mysql/share/charsets/ |
| datadir | /usr/local/mysql/data/ |
| innodb_data_home_dir | /data/mysql/data |
| innodb_log_group_home_dir | /data/mysql/data |
| innodb_max_dirty_pages_pct | 75 |
| lc_messages_dir | /usr/local/mysql/share/ |
| plugin_dir | /usr/local/mysql/lib/mysql/plugin/ |
| slave_load_tmpdir | /tmp |
| tmpdir | /tmp |
+-----------------------------------------+------------------------------------+
11 rows in set (0.01 sec)
从上面看确实是空间满了,然后调整变量“tmpdir”和“slave_load_tmpdir”,然后重启mysql服务,结果就ok了
[mysqld]
...
tmpdir=/data/mysql
slave_load_tmpdir=/data/mysql
...
[root@localhost mysql]# support-files/mysql.server restart
Shutting down MySQL (Percona Server).....[ OK ]
Starting MySQL (Percona Server)...[ OK ]
[root@localhost mysql]# bin/mysql
Welcome to the MySQL monitor. Commands end with ; or /g.
Your MySQL connection id is 1
Server version: 5.5.24-log Source distribution
Copyright (c) 2000, 2011, Oracle and/or its affiliates. All rights reserved.
Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.
Type 'help;' or '/h' for help. Type '/c' to clear the current input statement.
mysql> insert into t2 select * from t2;
ERROR 1046 (3D000): No database selected
mysql> use test;
Database changed
mysql> insert into t2 select * from t2;
Query OK, 98304 rows affected (4.48 sec)
Records: 98304 Duplicates: 0 Warnings: 0
这个就是我在改数据的目录时,忘记改这个变量值了。
----end----
bitsCN.com
MySQL is an open source relational database management system, mainly used to store and retrieve data quickly and reliably. Its working principle includes client requests, query resolution, execution of queries and return results. Examples of usage include creating tables, inserting and querying data, and advanced features such as JOIN operations. Common errors involve SQL syntax, data types, and permissions, and optimization suggestions include the use of indexes, optimized queries, and partitioning of tables.

MySQL is an open source relational database management system suitable for data storage, management, query and security. 1. It supports a variety of operating systems and is widely used in Web applications and other fields. 2. Through the client-server architecture and different storage engines, MySQL processes data efficiently. 3. Basic usage includes creating databases and tables, inserting, querying and updating data. 4. Advanced usage involves complex queries and stored procedures. 5. Common errors can be debugged through the EXPLAIN statement. 6. Performance optimization includes the rational use of indexes and optimized query statements.

MySQL is chosen for its performance, reliability, ease of use, and community support. 1.MySQL provides efficient data storage and retrieval functions, supporting multiple data types and advanced query operations. 2. Adopt client-server architecture and multiple storage engines to support transaction and query optimization. 3. Easy to use, supports a variety of operating systems and programming languages. 4. Have strong community support and provide rich resources and solutions.

InnoDB's lock mechanisms include shared locks, exclusive locks, intention locks, record locks, gap locks and next key locks. 1. Shared lock allows transactions to read data without preventing other transactions from reading. 2. Exclusive lock prevents other transactions from reading and modifying data. 3. Intention lock optimizes lock efficiency. 4. Record lock lock index record. 5. Gap lock locks index recording gap. 6. The next key lock is a combination of record lock and gap lock to ensure data consistency.

The main reasons for poor MySQL query performance include not using indexes, wrong execution plan selection by the query optimizer, unreasonable table design, excessive data volume and lock competition. 1. No index causes slow querying, and adding indexes can significantly improve performance. 2. Use the EXPLAIN command to analyze the query plan and find out the optimizer error. 3. Reconstructing the table structure and optimizing JOIN conditions can improve table design problems. 4. When the data volume is large, partitioning and table division strategies are adopted. 5. In a high concurrency environment, optimizing transactions and locking strategies can reduce lock competition.

In database optimization, indexing strategies should be selected according to query requirements: 1. When the query involves multiple columns and the order of conditions is fixed, use composite indexes; 2. When the query involves multiple columns but the order of conditions is not fixed, use multiple single-column indexes. Composite indexes are suitable for optimizing multi-column queries, while single-column indexes are suitable for single-column queries.

To optimize MySQL slow query, slowquerylog and performance_schema need to be used: 1. Enable slowquerylog and set thresholds to record slow query; 2. Use performance_schema to analyze query execution details, find out performance bottlenecks and optimize.

MySQL and SQL are essential skills for developers. 1.MySQL is an open source relational database management system, and SQL is the standard language used to manage and operate databases. 2.MySQL supports multiple storage engines through efficient data storage and retrieval functions, and SQL completes complex data operations through simple statements. 3. Examples of usage include basic queries and advanced queries, such as filtering and sorting by condition. 4. Common errors include syntax errors and performance issues, which can be optimized by checking SQL statements and using EXPLAIN commands. 5. Performance optimization techniques include using indexes, avoiding full table scanning, optimizing JOIN operations and improving code readability.


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