fil_init 主要是初始化文件打开指针哈希表，所有打开的文件全记录在 fil_system 之中，构造按名字查找的哈希表
buf_pool_init 内存缓冲池的初始化，对应 buf_pool_ptr 数组之中，还初始化了 adaptive hash index 的内存
log_init 初始化log缓冲区，默认大小为 512*16k， 每个log页面大小为 #define os_file_log_block_size 512 日志文件在创建过程中也是指定不用系统缓存
lock_sys_create 初始化系统锁，就是建了一个hash表，lock_sys
recv_recovery_from_checkpoint_start 开始执行恢复
dict_boot 初始化表结构的缓存，dict_sys，建两个hash表，可以根据表名和表id查找；初始化系统表，就四个 sys_tables sys_columns sys_indexes sys_fields ；初始化 insert buffer，每一个表空间对应一个；读入上面四个系统表中的内容
trx_sys_init_at_db_start 初初化事务结构体 trx_sys ； creates the global purge system control structure and inits the history
dict_create_or_check_foreign_constraint_tables 创建另外两张系统表 sys_foreign sys_foreign_cols
启动的线程，
io部分共10个，可通过参数配置
1个 insert buffer thread
1个 log thread
4个 aio read thread
4个 aio write thread
1个 lock timeout thread a thread which wakes up threads whose lock wait may have lasted too long
1个 error monitor thread a thread which prints warnings about semaphore waits which have lasted too long
1个 monitor thread a thread which prints the info output by various innodb monitors
1个 master thread the master thread controlling the server
1个 thread handle shutdown
1个 handle connections socket 专门用来处理连理的
1个 trx_rollback_or_clean_all_recovered rollback the uncommitted transactions which have no user session
struct st_mysql_plugin *mysql_optional_plugins[]=
{
builtin_innobase_plugin, builtin_perfschema_plugin, builtin_partition_plugin, 0
};
struct st_mysql_plugin *mysql_mandatory_plugins[]=
{
builtin_binlog_plugin, builtin_mysql_password_plugin, builtin_csv_plugin, builtin_heap_plugin, builtin_myisam_plugin, builtin_myisammrg_plugin, 0
};
初始化的 binlog memory myisam innodb pefformance_schema partition
，