MySQL storage engine
MySQL storage engine
Provided as a pluggable component
-MySQL service software that comes with the program function, process table processor
- different storage engines have different functions and data storage
The default storage engine
-MySQL 5.0/5.1 ---> MyISAM
-MySQL 5.5/5.6 ---> InnoDB
Example:
Execute SHOW ENGINES \ G can view a list of instructions, MySQL 5.6 storage engine available 9 species (except for the last FEDERATED, eight other support), which is used by default storage engine InnoDB
mysql> show engines\G *************************** 1. row *************************** Engine: InnoDB Support: DEFAULT Comment: Supports transactions, row-level locking, and foreign keys Transactions: YES XA: YES Savepoints: YES *************************** 2. row *************************** Engine: MRG_MYISAM Support: YES Comment: Collection of identical MyISAM tables Transactions: NO XA: NO Savepoints: NO *************************** 3. row *************************** Engine: MEMORY Support: YES Comment: Hash based, stored in memory, useful for temporary tables Transactions: NO XA: NO Savepoints: NO *************************** 4. row *************************** Engine: BLACKHOLE Support: YES Comment: /dev/null storage engine (anything you write to it disappears) Transactions: NO XA: NO Savepoints: NO *************************** 5. row *************************** Engine: MyISAM Support: YES Comment: MyISAM storage engine Transactions: NO XA: NO Savepoints: NO *************************** 6. row *************************** Engine: CSV Support: YES Comment: CSV storage engine Transactions: NO XA: NO Savepoints: NO *************************** 7. row *************************** Engine: ARCHIVE Support: YES Comment: Archive storage engine Transactions: NO XA: NO Savepoints: NO *************************** 8. row *************************** Engine: PERFORMANCE_SCHEMA Support: YES Comment: Performance Schema Transactions: NO XA: NO Savepoints: NO *************************** 9. row *************************** Engine: FEDERATED Support: NO Comment: Federated MySQL storage engine Transactions: NULL XA: NULL Savepoints: NULL 9 rows in set (0.00 sec)
Storage engine configuration
Changes to the table storage engine
Manually specify when construction of the table
- When not specified, the default storage engine
-show create table 表名\G；
mysql> mysql> mysql> create table innotb( -> id int(2) -> ) engine=innodb; Query OK, 0 rows affected (0.01 sec) mysql> show create table innotb; +--------+-------------------------------------------------------------------------------------------+ | Table | Create Table | +--------+-------------------------------------------------------------------------------------------+ | innotb | CREATE TABLE `innotb` ( `id` int(2) DEFAULT NULL ) ENGINE=InnoDB DEFAULT CHARSET=latin1 | +--------+-------------------------------------------------------------------------------------------+ 1 row in set (0.00 sec)
Set the default storage engine
/Etc/my.cnf modify configuration files
-default-storage-engine = storage engine name
[mysqld] # # Remove leading # and set to the amount of RAM for the most important data # cache in MySQL. Start at 70% of total RAM for dedicated server, else 10%. # innodb_buffer_pool_size = 128M # # Remove leading # to turn on a very important data integrity option: logging # changes to the binary log between backups. # log_bin # # Remove leading # to set options mainly useful for reporting servers. # The server defaults are faster for transactions and fast SELECTs. # Adjust sizes as needed, experiment to find the optimal values. # join_buffer_size = 128M # sort_buffer_size = 2M # read_rnd_buffer_size = 2M datadir=/var/lib/mysql socket=/var/lib/mysql/mysql.sock secure_file_priv="/myload" # Disabling symbolic-links is recommended to prevent assorted security risks symbolic-links=0 default-storage-engine=myisam log-error=/var/log/mysqld.log pid-file=/var/run/mysqld/mysqld.pid
mysql> show variables like 'default_storage_engine'; +------------------------+--------+ | Variable_name | Value | +------------------------+--------+ | default_storage_engine | MyISAM | +------------------------+--------+ 1 row in set (0.00 sec)
Storage Engine Features
myisam storage engine
main feature
- Support for table-level locking
- does not support transactions, the transaction is rolled back, foreign keys
Documents related tables
- table name .frm
- table name .MYI
- 表 名 .MYD
InnoDB storage engine
main feature
- supports row-level locking
- Support for the transaction, the transaction is rolled back, foreign keys
Documents related tables
- table name .frm, table name .ibd
-ibdata1
-ib_logfile0
-ib_logfile1
MySQL locking mechanism
Lock granularity
- table-level lock: once directly on the entire table to be locked.
- row-level locking: lock only a line
-页级锁：对整个页面（MySQL管理数据的基本存储单位）进行加锁
锁类型
-读锁（共享锁）：支持并发读
-写锁（互斥锁、排他锁）：是独占锁，上锁期间其他线程不能读表或写表
查看当前锁状态
-检查Table_lock开头的变量，%作通配符
mysql> show status like 'table_lock%'; +-----------------------+-------+ | Variable_name | Value | +-----------------------+-------+ | Table_locks_immediate | 100 | | Table_locks_waited | 0 | +-----------------------+-------+ 2 rows in set (0.00 sec)
事务引入
现实生活中，我们往往经常会进行转账操作，转账操作可以分为两部分来完成，转入和转出。只有这两部分都完成了才可以认为是转账成功。在数据库中，这个过程是使用两条语句来完成的，如果其中任意一条语句出现了异常没有执行，则会导致两个账号的金额不同步，造成错误。
为了防止上面可能出现的情况，MySQL引入了事务，所谓事务就是针对数据库的一组操作，它可以由一条或者多条SQL语句组成，同一个事务的操作具备同步的特点，如果其中有一条语句不能执行的话，那么所有的语句都不会执行，也就是说，事务中的语句要么都执行，要么都不执行。
在使用数据库时需要使用事务，必须先开启事务，具体语句如下：
mysql> start transaction; Query OK, 0 rows affected (0.00 sec)
上面语句是用来开启事务，事务开启之后就可以执行SQL语句，SQL语句执行成功之后，需要使用相应语句提交事务，提交事务的语句如下：
commit；
需要注意的是，在MySQL中直接书写的SQL语句都是自动提交的，而事务中的操作语句需要使用commit语句手动提交，只有事务提交后其中的操作才会生效。
如果不想提交事务，我们还可以使用相关语句取消事务（也称回滚），具体语句如下：
rollback；
需要注意的是，rollback语句只能针对未提交的事务执行的回滚操作，已经提交的事务是不能回滚的。
事务特性（ACID）
Atomic:原子性
-事务的整个操作是一个整体，不可分割，要么全部成功，要么全部失败。
Consistency；一致性
-事务操作的前后，表中的记录没有变化。
Isolation:隔离性
-事务曹总时相互隔离不受影响的。
Durability；持久性
-数据一旦提交，不可改变，永久改变表数据
例：
mysql> show variables like "autocommit";
+---------------+-------+
| Variable_name | Value |
+---------------+-------+
| autocommit | ON |
+---------------+-------+
1 row in set (0.00 sec)
mysql> set autocommit=off;
Query OK, 0 rows affected (0.00 sec)
mysql> show variables like "autocommit";
+---------------+-------+
| Variable_name | Value |
+---------------+-------+
| autocommit | OFF |
+---------------+-------+
1 row in set (0.00 sec)
mysql> select * from intab;
Empty set (0.00 sec)
mysql> desc intab;
+-------+------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+------------+------+-----+---------+-------+
| name | varchar(4) | YES | | NULL | |
+-------+------------+------+-----+---------+-------+
1 row in set (0.00 sec)
mysql> insert intab values("bob");
Query OK, 1 row affected (0.00 sec)
mysql> select * from intab;
+------+
| name |
+------+
| bob |
+------+
1 row in set (0.00 sec)
mysql> rollback;
Query OK, 0 rows affected (0.00 sec)
mysql> select * from intab;
Empty set (0.00 sec)