在使用mysql5.7的时候，发现了不少在mysql5.6上不曾见过的日志，级别为note, 最常见的note日志以下三种，下面我们来逐个解释。
第一种，Aborted connection . 如上图，信息如下：
2016-03-17T14:44:24.102542Z 59 [Note] Aborted connection 59 to db: ‘unconnected’ user: ‘mha’ host: ‘197.xx.xx.xx’ (Got an error reading communication packets)
2016-03-17T14:44:31.273897Z 61 [Note] Aborted connection 61 to db: ‘unconnected’ user: ‘mha’ host: ‘197.xx.xx.xx(Got an error reading communication packets)
2016-03-17T14:44:31.273897Z 61 [Note] Aborted connection 61 to db: ‘unconnected’ user: ‘mha’ host: ‘197.xx.xx.xx(Got an error reading communication packets)
2016-03-17T14:44:31.273897Z 61 [Note] Aborted connection 61 to db: ‘unconnected’ user: ‘mha’ host: ‘197.xx.xx.xx(Got timeout reading communication packets)
上面两个是连接中断的错误信息，原因不一样，Got an error reading communication packets 的原因是因为网络等原因导致。 Got timeout reading communication packets 这个错误的原因是会话的idle时间达到了数据库指定的timeout时间。
第二种：SLAVE多线程同步的信息
信息如下：
2016-03-14T15:48:26.432150Z 73 [Note]Multi-threaded slave statistics for channel ”: seconds elapsed = 121; eventsassigned = 100374529; worker queues filled over
overrun level = 0; waited due aWorker queue full = 0; waited due the total size = 0; waited at clock conflicts= 1451875661700 waited (count) when Workers occupied = 3211993 waited whenWorkers occupied = 445032386000
2016-03-14T15:50:28.398745Z 73 [Note]Multi-threaded slave statistics for channel ”: seconds elapsed = 122; eventsassigned = 100500481; worker queues filled over
overrun level = 0; waited due aWorker queue full = 0; waited due the total size = 0; waited at clock conflicts= 1452001865500 waited (count) when Workers occupied = 3211993 waited whenWorkers occupied = 445032386000
我们通过源代码，找到下面一段，该段实现了上述日志的输出。
if ((my_now
– rli->mts_last_online_stat)>=
mts_online_stat_period)
{
sql_print_information(“Multi-threadedslave
statistics%s: “
“seconds
elapsed = %lu; “
“events
assigned = %llu; “
“worker
queues filled over overrun level = %lu;”
“waited
due a Worker queue full = %lu; “
“waited
due the total size = %lu; “
“waited
at clock conflicts = %llu “
“waited(count)
when Workers occupied = %lu “
“waited
when Workers occupied = %llu”,
rli->get_for_channel_str(),
static_cast<unsignedlong>
(my_now – rli->mts_last_online_stat),
rli->mts_events_assigned,
rli->mts_wq_overrun_cnt,
rli->mts_wq_overfill_cnt,
rli->wq_size_waits_cnt,
rli->mts_total_wait_overlap,
rli->mts_wq_no_underrun_cnt,
rli->mts_total_wait_worker_avail);
rli->mts_last_online_stat=my_now;
通过这一句(my_now
– rli->mts_last_online_stat), 以及最后一句rli->mts_last_online_stat=my_now; 可以得知，
seconds elapsed 就是上一次统计跟这一次统计的时间间隔。
而mts_online_stat_period =120秒，硬代码，因此就是几乎每隔120秒，就有上述日志的输出。
通过进一步查看原代码，初步了解上述日志信息的含义，如下：
events assigned：总共有多少个event被分配执行，计的是总数。
worker queues filled over overrun level：多线程同步中，worker 的私有队列长度超长的次数，计的是总数。
waited due a Worker queue full ：因为worker的队列超长而产生等待的次数，计的是总数。
waited due the total size ：超过最大size的次数，这个由参数slave_pending_jobs_size_max 指定。
waited at clock conflicts ：因为逻辑时间产生冲突的等待时间，单位是纳秒。
waited (count) when Workers occupied ：因为workder被占用而出现等待的次数。（总计值）。
waited when Workersoccupied ：因为workder被占用而出现等待的总时间，总计值，单位是纳秒。
第三种：page_cleaner线程的输出日志
如图，信息如下：
2016-03-24T17:45:28.005117Z 0 [Note] InnoDB:page_cleaner: 1000ms intended loop took 4750ms.The
settings might not be optimal. (flushed=1519 and evicted=0, during the time.)
查找源代码，发现是上面的日志由下面一段代码输出：
if (ret_sleep
== OS_SYNC_TIME_EXCEEDED) {
ulint
curr_time = ut_time_ms();
if (curr_time
>next_loop_time + 3000) {
if (warn_count
== 0) {
ib::info()
<< “page_cleaner: 1000ms”
” intended
loop took “
<<1000 + curr_time
– next_loop_time
<<“ms. The
settings might not”
” be optimal.
(flushed=”
<<n_flushed_last
<<” and evicted=”
<<n_evicted
<<“, during
the time.)”;
if (warn_interval
>300) {
warn_interval= 600;
}else {
warn_interval*= 2;
}
warn_count= warn_interval;
} else {
–warn_count;
}
} else {
/* reset counter */
warn_interval= 1;
warn_count= 0;
}
next_loop_time= curr_time + 1000;
n_flushed_last= n_evicted = 0;
}
通过分析源代码， 输出上述日志的条件是curr_time> next_loop_time + 3000 ，即比原定的循环时间next_loop_time多3000毫秒，而next_loop_time的标准时间是1000毫秒，即1秒钟做一次刷新页的操作。
loop took 4750ms ，即是这次刷新循环的实际经历时间。
后面还有一个(flushed=1519 and evicted=0,during the time.)这样的日志，即对应n_flushed_last与n_evicted 变量，而这两个变量又由n_flushed_list与n_flushed_lru赋值。
./storage/innobase/buf/buf0flu.cc:3322: n_flushed_last +=n_flushed_list;
./storage/innobase/buf/buf0flu.cc:3321: n_evicted += n_flushed_lru;
而n_flushed_list与n_flushed_lru赋值函数为pc_wait_finished，如下，我们来看看该函数的注释。
pc_wait_finished(&n_flushed_lru,&n_flushed_list);
/**
Wait until all flush requests are finished.
@param n_flushed_lru numberof pages flushed from the end of the LRU list.
@param n_flushed_list numberof pages flushed from the end of the
flush_list.
@return trueif all flush_list flushing batch were success. */
static
bool
pc_wait_finished(
ulint* n_flushed_lru,
ulint* n_flushed_list)
{
。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。
}
通过源代码的注释，我们获知如下信息：
n_flushed_lru number of pages flushed from the end of the LRU list.
n_flushed_lru 这个值表示从lru 列表尾部刷新的页数，也就是日志中如evicted=0 指标的所表示的值，如果该值不为零，则存在innodb buffer不够的嫌疑。
n_flushed_list 这个是从刷新列表中刷新的页数，也就是脏页数，也就是日志中flushed=1519 的值。
