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本篇内容介绍了“Innodb 怎么自动开启打印 show engine status 到 err 日志”的有关知识，在实际案例的操作过程中，不少人都会遇到这样的困境，接下来就让丸趣 TV 小编带领大家学习一下如何处理这些情况吧！希望大家仔细阅读，能够学有所成！
一、问题描述
为什么我的 err 日志里面有大量的 show engine innodb status 的记录，我自己并没有开启 innodb_status_output 参数。
二、问题分析
通过查看日志，发现如下输出：
2019-03-21T17:00:02.375231Z 1230497 [Warning] InnoDB: Difficult to find free blocks in the buffer pool (338 search iterations)! 0 failed attempts to flush a page! Consider increasing the buffer pool size. It is also possible
that in your Unix version fsync is very slow, or completely frozen inside the OS kernel. Then upgrading to a
newer version of your operating system may help. Look at the number of fsyncs in diagnostic info below.
Pending flushes (fsync) log: 0; buffer pool: 0. 1446962050 OS file reads, 545881917 OS file writes,
376257282 OS fsyncs. Starting InnoDB Monitor to print further diagnostics to the standard output.日志也写得很清楚。应该是 free block 不够了 Innodb 自动开启了。但是我们需要源码验证一下。
三、源码验证
在源码的 buf_LRU_handle_lack_of_free_blocks 函数中我们看到如下：
if ((current_ms started_ms + 2000)
(current_ms last_printout_ms + 2000)
srv_buf_pool_old_size == srv_buf_pool_size) { ib::warn() Difficult to find free blocks in the buffer pool
( n_iterations search iterations)!
flush_failures failed attempts to
flush a page! Consider increasing the buffer pool
size. It is also possible that in your Unix version
fsync is very slow, or completely frozen inside
the OS kernel. Then upgrading to a newer version
of your operating system may help. Look at the
number of fsyncs in diagnostic info below.
Pending flushes (fsync) log:
fil_n_pending_log_flushes
buffer pool:
fil_n_pending_tablespace_flushes
. os_n_file_reads OS file reads,
os_n_file_writes OS file writes,
os_n_fsyncs
OS fsyncs. Starting InnoDB Monitor to print
further diagnostics to the standard output.
last_printout_ms = current_ms;
*mon_value_was = srv_print_innodb_monitor;
*started_monitor = true;
srv_print_innodb_monitor = true;
os_event_set(srv_monitor_event);这里不仅打印出了日志同时设置了参数 srv_print_innodb_monitor = true; 并且开始 os_event_set(srv_monitor_event); 开启了 monitor 打印线程。那我们看看 srv_print_innodb_monitor 对应什么参数呢。如下：
static MYSQL_SYSVAR_BOOL(status_output, srv_print_innodb_monitor,
PLUGIN_VAR_OPCMDARG, Enable InnoDB monitor output to the error log. , NULL, innodb_status_output_update, FALSE);实际上就是 innodb_status_output 被自动开了。当然如果查看调用可以在上层函数 buf_LRU_get_free_block 中查看到调用，实际上就是在 free list 找不到空闲的 block 的时候会做输出。buf_LRU_get_free_block 还包含了一个块的分配流程大约如下，可自行参考：
If there is a block in the free list, take it . 如果这里找不到就会自动开启 innodb_status_output
If no block was in the free list, search from the end of the LRU list and try to free a block there.
No free block was found: try to flush the LRU list.
“Innodb 怎么自动开启打印 show engine status 到 err 日志”的内容就介绍到这里了，感谢大家的阅读。如果想了解更多行业相关的知识可以关注丸趣 TV 网站，丸趣 TV 小编将为大家输出更多高质量的实用文章！
