innodb中master线程的调度的算法改进(mysql 5.6.26)
作者：周琳
QQ:715169549
源码交流群：196380905
1.master线程的调度：
/*********************************************************************//**
The master thread controlling the server.
os_thread_ret_t DECLARE_THREAD(srv_master_thread)
如下是核心代码：
ulint old_activity_count = srv_get_activity_count();
if (srv_force_recovery >= SRV_FORCE_NO_BACKGROUND) {
goto suspend_thread;
}
while (srv_shutdown_state == SRV_SHUTDOWN_NONE) {
/*在linux下就是1000000/1000000，在针对这个整除的值%1000000;
*这个就是os_thread_sleep( microseconds);的计算方式
srv_master_sleep(); //
MONITOR_INC(MONITOR_MASTER_THREAD_SLEEP);
/*很显然并没有按照1秒和10秒的算法来，而是通过当前服务器活动的数量来决定。
if (srv_check_activity(old_activity_count)) { //srv_check_activity(old_activity_count)返回：return(srv_sys->activity_count != old_activity_count);
old_activity_count = srv_get_activity_count(); //srv_get_activity_count返回:return(srv_sys->activity_count);
srv_master_do_active_tasks();
} else {
srv_master_do_idle_tasks();
}
}
while (srv_master_do_shutdown_tasks(&last_print_time)) {
/* Shouldn't loop here in case of very fast shutdown */
ut_ad(srv_fast_shutdown < 2);
}
}
srv_master_do_active_tasks做的事情：
//#define PCT_IO(p) ((ulong) (srv_io_capacity * ((double) (p) / 100.0)))
//# define SRV_MASTER_CHECKPOINT_INTERVAL (7)
1.log_free_check，检查是否有空闲的log buffer。
2.ibuf_contract_in_background(0, FALSE),合并PCT_IO(5)个插入缓冲
3.srv_sync_log_buffer_in_background,后台同步刷新log buffer日志到log file
4.cur_time % SRV_MASTER_CHECKPOINT_INTERVAL == 0,就做log_checkpoint(TRUE, FALSE)，而log_checkpoint仅仅是检查bp中的lsn以及把lsn的值写入到redo file中。
真正做检查点刷新脏页到磁盘的是log_make_checkpoint_at函数。
srv_master_do_idle_tasks做的事情：
1.log_free_check，检查是否有空闲的log buffer。
2.ibuf_contract_in_background(0, TRUE),合并PCT_IO(100)个插入缓冲.
3.srv_sync_log_buffer_in_background,刷新log buffer到磁盘。
4.cur_time % SRV_MASTER_CHECKPOINT_INTERVAL == 0,就做log_checkpoint(TRUE, FALSE)，而log_checkpoint仅仅是检查bp中的lsn以及把lsn的值写入到redo file中。
真正做检查点刷新脏页到磁盘的是log_make_checkpoint_at函数。
如下是srv_sys_t结构：
元素包含一个线程表和一个task queue。
/** The server system struct */
struct srv_sys_t{
ib_mutex_t tasks_mutex; /*!< variable protecting the
tasks queue */
UT_LIST_BASE_NODE_T(que_thr_t)
tasks; /*!< task queue */
ib_mutex_t mutex; /*!< variable protecting the
fields below. */
ulint n_sys_threads; /*!< size of the sys_threads
array */
srv_slot_t* sys_threads; /*!< server thread table */
ulint n_threads_active[SRV_MASTER + 1];
/*!< number of threads active
in a thread class */
srv_stats_t::ulint_ctr_1_t
activity_count; /*!< For tracking server
activity */
};
接下来介绍下activity_count,这个函数是由srv_inc_activity_count(srv_sys->activity_count.inc();)进行自增的,这个函数会在哪些动作中调用呢？
我们看下调用该函数的函数流程：
1.row_undo_step：在表中回滚一行的操作
->srv_inc_activity_count()
2.srv_active_wake_master_thread：如果需要主线程处理，切主线程处于挂起状态就唤醒主线程。
->srv_inc_activity_count()
3.srv_wake_master_thread:如果主线程挂起或者正在被挂起，唤醒主线程。
->srv_inc_activity_count()
上述函数还被很多函数调用，activity_count可以理解为mysql运行中操作的计数器，每个操作都会累加。所以master线程依据时间间隔的
activity_count计数器来判断执行srv_master_do_active_tasks还是srv_master_do_idle_tasks。可以看出这个计数器如果在1秒以后这个值如果
不发生变化就切换到srv_master_do_idle_tasks。
2.page cleaner线程：(buf0flu.c中)
核心代码：
ulint next_loop_time = ut_time_ms() + 1000;
while (srv_shutdown_state == SRV_SHUTDOWN_NONE) {//服务器没有关闭的状态下
/* The page_cleaner skips sleep if the server is
idle and there are no pending IOs in the buffer pool
and there is work to do. */
if (srv_check_activity(last_activity) //检查当前服务器的活动次数
|| buf_get_n_pending_read_ios()
|| n_flushed == 0) {
page_cleaner_sleep_if_needed(next_loop_time); //休眠min(1000000,(next_loop_time-当前时间)*1000))
}
next_loop_time = ut_time_ms() + 1000; //重新计算当前next_loop_time值
if (srv_check_activity(last_activity)) { //检查当前服务器活动数量
last_activity = srv_get_activity_count();
/* Flush pages from end of LRU if required */
n_flushed = buf_flush_LRU_tail();
/* Flush pages from flush_list if required */
n_flushed += page_cleaner_flush_pages_if_needed();
} else {
n_flushed = page_cleaner_do_flush_batch(
PCT_IO(100), //刷新srv_io_capacity个脏页到磁盘
LSN_MAX);
}
}
if (srv_fast_shutdown == 2) {
/* In very fast shutdown we simulate a crash of
buffer pool. We are not required to do any flushing */
goto thread_exit;
}
do {
n_flushed = page_cleaner_do_flush_batch(PCT_IO(100), LSN_MAX); //刷新srv_io_capacity个脏页到磁盘
/* We sleep only if there are no pages to flush */
if (n_flushed == 0) {
os_thread_sleep(100000); //休眠1秒
}
} while (srv_shutdown_state == SRV_SHUTDOWN_CLEANUP);
do {
success = buf_flush_list(PCT_IO(100), LSN_MAX, &n_flushed);
buf_flush_wait_batch_end(NULL, BUF_FLUSH_LIST);
} while (!success || n_flushed > 0);
