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本篇內容介紹了“Innodb 怎么自動開啟打印 show engine status 到 err 日志”的有關知識，在實際案例的操作過程中，不少人都會遇到這樣的困境，接下來就讓丸趣 TV 小編帶領大家學習一下如何處理這些情況吧！希望大家仔細閱讀，能夠學有所成！
一、問題描述
為什么我的 err 日志里面有大量的 show engine innodb status 的記錄，我自己并沒有開啟 innodb_status_output 參數。
二、問題分析
通過查看日志，發現如下輸出：
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.日志也寫得很清楚。應該是 free block 不夠了 Innodb 自動開啟了。但是我們需要源碼驗證一下。
三、源碼驗證
在源碼的 buf_LRU_handle_lack_of_free_blocks 函數中我們看到如下：
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);這里不僅打印出了日志同時設置了參數 srv_print_innodb_monitor = true; 并且開始 os_event_set(srv_monitor_event); 開啟了 monitor 打印線程。那我們看看 srv_print_innodb_monitor 對應什么參數呢。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);實際上就是 innodb_status_output 被自動開了。當然如果查看調用可以在上層函數 buf_LRU_get_free_block 中查看到調用，實際上就是在 free list 找不到空閑的 block 的時候會做輸出。buf_LRU_get_free_block 還包含了一個塊的分配流程大約如下，可自行參考：
If there is a block in the free list, take it . 如果這里找不到就會自動開啟 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 怎么自動開啟打印 show engine status 到 err 日志”的內容就介紹到這里了，感謝大家的閱讀。如果想了解更多行業相關的知識可以關注丸趣 TV 網站，丸趣 TV 小編將為大家輸出更多高質量的實用文章！
