## mysql
MySQL 是一个开源的关系型数据库管理系统。
- 官网:
- 源码:
- 文档:
- 开源:
## 下载安装
### Ubuntu安装MySQL
安装服务器与客户端
```
sudo apt-get install mysql-server mysql-client
```
相关目录与文件
- 配置目录 /etc/mysql/
- 运行状态 /var/run/mysqld/
- 日志目录 /var/log/mysql/
- 数据目录 /var/lib/mysql/
- 其它文件 /var/lib/mysql-files/
- 动态插件 /usr/lib/mysql/plugin/
## 基础命令
初次登录，直接用安装时设置的密码连接
```
$ mysql -u root -p
Enter password
mysql>
```
查看帮助信息
```
mysql> help
...
```
其中常用的命令有
- status 查看当前状态
- system 调用系统shell命令
- source 加载并执行sql文件
- delimiter 设置行分隔符
- connect 重新连接服务器
- use 切换数据库
### 配置操作
mysql启动时会从/etc/mysql/my.cnf加载配置，show variables;可以查看当前配置
### 数据库操作
- 查看 show databases
- 切换 use demo
- 创建 create database demo
- 删除 drop database demo
查看数据库列表
```
mysql> show databases;
```
创建数据库
```
mysql> create database demo;
```
切换数据库
```
mysql> use demo;
```
删除数据库
```
mysql> drop database demo;
```
### 关系表操作
- 查看 show tables
- 创建 create table demo(a int)
- 修改 alter table add column b int
- 查看 desc demo
- 删除 drop table demo
### 数据操作
- 查询 select * from demo
- 添加 insert into demo values(1,2)
- 修改 update demo set a=1, b=2 where a=3
- 删除 delete from demo where a=1
## 存储引擎
- 源码：
- 文档：
```
mysql> show engines;
```
|engine|comment|
|------|-------|
|InnoDB| supports transactions, row-level locking, and foreign keys|
|MyISAM| |
|MEMORY|hash based, stored in memory, useful for temporary tables|
|BLACKHOLE| |
|ARCHIVE| |
|CSV| |
|MRG_MYISAM| |
|PERFORMANCE_SCHEMA| |
|FEDERATED| |
### InnoDB
InnoDB是一种支持ACID事务的存储引擎
- 源码：
- 文档：
InnoDB是多线程的，通过命令可以看各线程的状态
```
mysql> show engine innodb status\G
```
|meta|task|
|------|----|
|BACKGROUND| 主线程 |
|FILE I/O| IO线程 |
|INSERT BUFFER AND HASH INDEX| 插入缓存与哈希索引 |
|SEMAPHORES| |
|TRANSACTIONS| |
|BUFFER POOL AND MEMORY| |
|ROW OPERATIONS| |
|LOG| |
#### 线程与缓存
MySQL的存储引擎是模块化，所以需要注册模块信息
```
// 注册模块 struct st_mysql_plugin {} // mysql-5.5.62/include/mysql/plugin.h:423
mysql_declare_plugin(innobase) { // mysql-5.5.62/storage/innobase/handler/ha_innodb.cc:11925
MYSQL_STORAGE_ENGINE_PLUGIN,
&innobase_storage_engine,
innobase_hton_name,
plugin_author,
"Supports transactions, row-level locking, and foreign keys",
PLUGIN_LICENSE_GPL,
innobase_init, /* Plugin Init */
NULL, /* Plugin Deinit */
INNODB_VERSION_SHORT,
innodb_status_variables_export,/* status variables */
innobase_system_variables, /* system variables */
NULL, /* reserved */
0, /* flags */
}
...
mysql_declare_plugin_end;
```
InnoDB在初始化函数中，会注册各种回调函数，并启动各种工作线程
```
innobase_init() // mysql-5.5.62/storage/innobase/handler/ha_innodb.cc:2218
// 注册各种回调函数 struct handlerton {} // mysql-5.5.62/sql/handler.h:705
innobase_hton->state = SHOW_OPTION_YES;
innobase_hton->db_type= DB_TYPE_INNODB;
innobase_hton->savepoint_offset=sizeof(trx_named_savept_t);
innobase_hton->close_connection=innobase_close_connection;
innobase_hton->savepoint_set=innobase_savepoint;
innobase_hton->savepoint_rollback=innobase_rollback_to_savepoint;
innobase_hton->savepoint_release=innobase_release_savepoint;
innobase_hton->commit=innobase_commit;
innobase_hton->rollback=innobase_rollback;
innobase_hton->prepare=innobase_xa_prepare;
innobase_hton->recover=innobase_xa_recover;
innobase_hton->commit_by_xid=innobase_commit_by_xid;
innobase_hton->rollback_by_xid=innobase_rollback_by_xid;
innobase_hton->create_cursor_read_view=innobase_create_cursor_view;
innobase_hton->set_cursor_read_view=innobase_set_cursor_view;
innobase_hton->close_cursor_read_view=innobase_close_cursor_view;
innobase_hton->create=innobase_create_handler;
innobase_hton->drop_database=innobase_drop_database;
innobase_hton->panic=innobase_end;
innobase_hton->start_consistent_snapshot=innobase_start_trx_and_assign_read_view;
innobase_hton->flush_logs=innobase_flush_logs;
innobase_hton->show_status=innobase_show_status;
innobase_hton->flags=HTON_SUPPORTS_FOREIGN_KEYS;
innobase_hton->release_temporary_latches=innobase_release_temporary_latches;
// 启动各种工作线程
innobase_start_or_create_for_mysql() // srv/srv0start.c:1028
os_thread_create(io_handler_thread, NULL, NULL);
os_thread_create(&srv_lock_time_thread, NULL, NULL);
os_thread_create(&srv_error_monitor_thread, NULL, NULL);
os_thread_create(&srv_monitor_thread, NULL, NULL);
os_thread_create(&srv_master_thread, NULL, NULL);
os_thread_create(&srv_purge_thread, NULL, NULL);
```
主线程
```
srv_master_thread() // mysql-5.5.62/storage/innobase/srv/srv0srv.c:2748
loop:
srv_main_1_second_loops++;
// 同步日志缓存
srv_sync_log_buffer_in_background(); // srv/srv0srv.c:2702
log_buffer_sync_in_background(TRUE); // log/log0log.c:1689
log_write_up_to(lsn, LOG_NO_WAIT, flush);
mutex_enter(&(log_sys->mutex));
log_sys->write_lsn = log_sys->lsn;
fil_flush(group->space_id); // fil/fil0fil.c:4755
mutex_enter(&fil_system->mutex);
os_file_flush(file); // os/os0file.c:2119
os_file_fsync(file);
fsync(file);
// 合并插入缓存
ibuf_contract_for_n_pages(FALSE, PCT_IO(5));
// 刷新数据缓存
buf_flush_list(PCT_IO(100), IB_ULONGLONG_MAX); // buf/buf0flu.c:1928
buf_flush_batch(buf_pool, BUF_FLUSH_LRU, min_n, 0);
buf_pool_mutex_enter(buf_pool);
buf_flush_LRU_list_batch(buf_pool, min_n);
buf_flush_flush_list_batch(buf_pool, min_n, lsn_limit);
buf_flush_buffered_writes();
mutex_enter(&(trx_doublewrite->mutex));
buf_flush_sync_datafiles();
// 执行清理任务
srv_master_do_purge();
trx_purge(srv_purge_batch_size); // trx/trx0purge.c:1139
rw_lock_x_lock(&purge_sys->latch);
thr = que_fork_start_command(purge_sys->query);
que_run_threads(thr);
background_loop:
srv_main_background_loops++;
row_drop_tables_for_mysql_in_background(); // row/row0mysql.c:2253
mem_free(drop->table_name);
flush_loop:
srv_main_flush_loops++;
log_checkpoint(TRUE, FALSE); // log/log0log.c:2077
log_groups_write_checkpoint_info();
log_group_checkpoint(group);
suspend_thread:
srv_suspend_thread(slot);
```
- 插入缓存与两次写
- 自适应哈希索引
- 启动、恢复、关闭
- 引擎插件升级
#### 各种文件
配置文件，MySQL在启动时会加载配置文件，这些配置在运行时也可以随时读写
- show variables;
- show variables like 'timeout';
- set [global|session] var=val
日志文件
数据文件
### MyISAM
- 源码：
- 文档：