MySQL数据库诊断：InnoDB关机问题

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4k 2023-06-08 16:25:44 博主文章分类：mysql-基础

问题描述，今天发现一台db服务器，错误日志中有innodb 报错信息，具体如下：

space 1131 offset 1221565 (448 records, index id 2730)
  206 InnoDB: Submit a detailed bug report to http://bugs.mysql.com
  209 2015-01-27 14:47:03 30309 [Warning] 'proxies_priv' entry '@ root@cndb012.5405.zr.sh.gcimg.net
      ' ignored in --skip-name-resolve mode.
  210 InnoDB: Warning: a long semaphore wait:
  211 --Thread 139840252565248 has waited at row0upd.cc line 2391 for 241.00 seconds the semaphore:
  212 X-lock (wait_ex) on RW-latch at 0x7f30e81ffec0 created in file buf0buf.cc line 994
  213 a writer (thread id 139840252565248) has reserved it in mode  wait exclusive
  214 number of readers 1, waiters flag 0, lock_word: ffffffffffffffff
  215 Last time read locked in file btr0sea.cc line 931
  216 Last time write locked in file /root/mysql-5.6.10/storage/innobase/row/row0upd.cc line 2391
  217 InnoDB: ###### Starts InnoDB Monitor for 30 secs to print diagnostic info:
  218 InnoDB: Pending preads 1, pwrites 0
  219 
  220 =====================================
  221 2015-02-17 01:33:24 7f2f1c5cd700 INNODB MONITOR OUTPUT
  222 =====================================
  223 Per second averages calculated from the last 9 seconds
  224 -----------------
  225 BACKGROUND THREAD
  226 -----------------
  227 srv_master_thread loops: 9485924 srv_active, 0 srv_shutdown, 12079 srv_idle                  
  228 srv_master_thread log flush and writes: 9498003
  229 ----------
  230 SEMAPHORES
  231 ----------
  232 OS WAIT ARRAY INFO: reservation count 20878957
  233 --Thread 139840305547008 has waited at srv0srv.cc line 2642 for 0.00 seconds the semaphore:
  234 X-lock (wait_ex) on RW-latch at 0x17dcce78 created in file trx0purge.cc line 128
  235 a writer (thread id 139840305547008) has reserved it in mode  wait exclusive
 cndb012.5405.zr.sh.gcimg.net.err                                                227,1          11%
 a writer (thread id 139840252565248) has reserved it in mode  wait exclusive                 
  242 number of readers 1, waiters flag 0, lock_word: ffffffffffffffff
  243 Last time read locked in file btr0sea.cc line 931
  244 Last time write locked in file /root/mysql-5.6.10/storage/innobase/row/row0upd.cc line 2391
  245 OS WAIT ARRAY INFO: signal count 24461907
  246 Mutex spin waits 46796216, rounds 120553500, OS waits 2922505
  247 RW-shared spins 27488053, rounds 494141792, OS waits 11545932
  248 RW-excl spins 6660716, rounds 158988739, OS waits 3758819
  249 Spin rounds per wait: 2.58 mutex, 17.98 RW-shared, 23.87 RW-excl
  250 ------------
  251 TRANSACTIONS
  252 ------------
  253 Trx id counter 34084627765
  254 Purge done for trx's n:o < 33966059091 undo n:o < 0 state: running but idle
  255 History list length 58473189
  256 LIST OF TRANSACTIONS FOR EACH SESSION:
  257 ---TRANSACTION 34084627619, ACTIVE 207 sec
  258 MySQL thread id 10667405, OS thread handle 0x7f2f164f6700, query id 6964941502 192.168.2.55 m
      ha_user cleaning up
  259 Trx read view will not see trx with id >= 34084627620, sees < 33966059089
  260 ---TRANSACTION 34084627590, ACTIVE 243 sec

。。。。。。。。。。。。。。。。。截取部分日志，网上搜到姜老师写的文章，拿来

存储，学习，共享

前段时间遇到一个问题，DBA反映有台MySQL数据库非常诡异，在无任何操作的前提下，磁盘IO负载都几乎跑满。然后跑了3、4个小时磁盘负载依旧。DBA的初步判断认为是RAID卡出了问题(之前遇到过类似RAID卡BBU问题导致负载较高)。不过既然是数据库无任何操作，那么即使RAID卡出现问题，也不应该出现这个问题。因此在调查了问题现场后，询问了DBA之前做了哪些操作，之后我便大致定位到了问题所在。

　　DBA的反馈是之前在做sysbench的全update性能测试，测试完成后就关闭了数据库。但是当再重启后就发现这个现象，并且等待3，4个小时候后问题依旧。待其叙述完后，我的第一反映是srv_innodb_fast_shutdown默认值为1，在关闭是不会对change buffer进行合并操作，因此会再下次启动时进行这类操作。因为MySQL 5.5版本InnoDB存储引擎的change buffer可以使用到1/2的Buffer Pool，故可能测试时期的update操作大部分都在change buffer中完成，再次启动会导致大量的合并操作。

　　问题可能是定位了，然而怎么证明我的想法又是另外一个过程了。首先根据DBA的描述，我在测试服务器上进行了类似的sysbench测试，然后关闭数据库，并对数据库进行备份以便再次进行观察。当再次启动MySQL数据库后，通过命令iotop可以观察到如下的运行状态：

`Total DISK READ: 32.55 M/s \| Total DISK WRITE: 0.00 B/s TID PRIO USER DISK READ DISK WRITE SWAPIN IO> COMMAND 535 be/4 mysql 3.26 M/s 0.00 B/s 0.00 % 80.88 % mysqld --basedir=... 536 be/4 mysql 29.26 M/s 0.00 B/s 0.00 % 71.93 % mysqld --basedir=... ......`

Total DISK READ: 32.55 M/s | Total DISK WRITE: 0.00 B/s 
 TID  PRIO  USER     DISK READ  DISK WRITE  SWAPIN     IO>    COMMAND 
 535  be/4 mysql       3.26 M/s    0.00 B/s  0.00 % 80.88 % mysqld --basedir=... 
 536 be/4 mysql      29.26 M/s    0.00 B/s  0.00 % 71.93 % mysqld --basedir=... 
 ......

　　可以发现的确有两个线程的IO负载较高，但是这两个进程对应于MySQL数据库的哪两个线程就不得而知了。接着，通过命令SHOW ENGINE INNODB STATUS可以观察到如下的内容：

`-------------- ROW OPERATIONS -------------- ...... Main thread process no. 535, id 140593741342464, state: doing insert buffer merge Purge thread process no. 536, id 140593707771648 ......`

　　这里可以看到Main thread process显示当前的状态为doing insert buffer merge，可以判断当正在处理change buffer。MySQL对命令SHOW ENGINE INNODB STATUS进行小小的改进，可以看到每个线程对应于Linux的进程号，也就是iotop对于的进程号，而默认只能看到对应的线程号。配置文件中启用了innodb_purge_thread=1，因此还可以看到purge线程的信息。

　　可以发现进行535和536就是上述iotop中IO负载较高的进程。因此问题基本已经被证实。然而通过iotop发现，purge线程的IO负载要比main线程的要高许多。这是之前没有特别注意的，虽然InnoDB快速关闭不会进行change buffer的合并操作，但是其也不会等待purge操作全部完成。而之前的测试产生了大量的undo log需要等待被purge。通过命令SHOW ENGINE INNODB STATUS发现：

`------------ TRANSACTIONS ------------ Trx id counter 12552900 Purge done for trx's n:o < ECEB125 undo n:o < 0 History list length 29572089`

　　可以看到History list length为29 572 089，也就是说差不多有接近3000W的undo log记录。OMG,还真不少。。。不过也好理解，毕竟测试的都是update操作。

　　另外，还可通过类似pstack工具找出当前MySQL数据库线程调用的函数信息：

5154 pthread_cond_wait,os_event_wait_low,log_write_up_to,trx_commit_complete_for_mysql,innobase_commit,ha_commit_trans,trans_commit_stmt,mysql_execute_command,mysql_parse,dispatch_command,do_handle_one_connection,handle_one_connection,start_thread(libpthread.so.0),clone(libc.so.6),?? 5008 libaio::??(libaio.so.1),os_aio_linux_handle,fil_aio_wait,io_handler_thread,start_thread(libpthread.so.0),clone(libc.so.6),?? 1701 pthread_cond_wait,os_event_wait_low,buf_flush_wait_batch_end,log_check_margins,row_upd_step,row_update_for_mysql,ha_innobase::update_row,handler::ha_update_row,mysql_update,mysql_execute_command,mysql_parse,dispatch_command,do_handle_one_connection,handle_one_connection,start_thread(libpthread.so.0),clone(libc.so.6),?? ...... 384 pread64(libpthread.so.0),os_file_pread,os_file_read_func,os_aio_func,fil_io,buf_read_page_low,buf_read_page,buf_page_get_gen,trx_purge_rseg_get_next_history_log,trx_purge_get_next_rec,row_purge_step,que_run_threads,trx_purge,srv_purge_thread,start_thread(libpthread.so.0),clone(libc.so.6),?? 273 read(libpthread.so.0),my_real_read,my_net_read,do_command,do_handle_one_connection,handle_one_connection,start_thread(libpthread.so.0),clone(libc.so.6),?? ...... 128 pread64(libpthread.so.0),os_file_pread,os_file_read_func,os_aio_func,fil_io,buf_read_page_low,buf_read_page,buf_page_get_gen,btr_cur_latch_leaves,btr_cur_search_to_nth_level,btr_pcur_restore_position_func,ibuf_restore_pos,ibuf_delete_rec,ibuf_merge_or_delete_for_page,buf_read_ibuf_merge_pages,ibuf_contract_ext,ibuf_contract_for_n_pages,srv_master_thread,start_thread(libpthread.so.0),clone(libc.so.6),??

5154 pthread_cond_wait,os_event_wait_low,log_write_up_to,trx_commit_complete_for_mysql,innobase_commit,ha_commit_trans,trans_commit_stmt,mysql_execute_command,mysql_parse,dispatch_command,do_handle_one_connection,handle_one_connection,start_thread(libpthread.so.0),clone(libc.so.6),?? 
 5008 libaio::??(libaio.so.1),os_aio_linux_handle,fil_aio_wait,io_handler_thread,start_thread(libpthread.so.0),clone(libc.so.6),?? 
 1701 pthread_cond_wait,os_event_wait_low,buf_flush_wait_batch_end,log_check_margins,row_upd_step,row_update_for_mysql,ha_innobase::update_row,handler::ha_update_row,mysql_update,mysql_execute_command,mysql_parse,dispatch_command,do_handle_one_connection,handle_one_connection,start_thread(libpthread.so.0),clone(libc.so.6),?? 
 ...... 
 384 pread64(libpthread.so.0),os_file_pread,os_file_read_func,os_aio_func,fil_io,buf_read_page_low,buf_read_page,buf_page_get_gen,trx_purge_rseg_get_next_history_log,trx_purge_get_next_rec,row_purge_step,que_run_threads,trx_purge,srv_purge_thread,start_thread(libpthread.so.0),clone(libc.so.6),?? 
 273 read(libpthread.so.0),my_real_read,my_net_read,do_command,do_handle_one_connection,handle_one_connection,start_thread(libpthread.so.0),clone(libc.so.6),?? 
 ...... 
 128 pread64(libpthread.so.0),os_file_pread,os_file_read_func,os_aio_func,fil_io,buf_read_page_low,buf_read_page,buf_page_get_gen,btr_cur_latch_leaves,btr_cur_search_to_nth_level,btr_pcur_restore_position_func,ibuf_restore_pos,ibuf_delete_rec,ibuf_merge_or_delete_for_page,buf_read_ibuf_merge_pages,ibuf_contract_ext,ibuf_contract_for_n_pages,srv_master_thread,start_thread(libpthread.so.0),clone(libc.so.6),??

　　可以看到有大量的trx_purge，ibuf_contract_for_n_pages函数调用，也就是purge和change buffer的操作。从这里也可以进一步证实之前的猜测。pstack的另一个好处是可以看到线程具体的函数调用情况，这里通过之前SHOW ENGINE INNODB STATUS得到的main线程号140593741342464(对于十六进制0x7FDE8802A700)可以看到该线程的函数调用：

Thread 5 (Thread 0x7fde8802a700 (LWP 535)): #0 0x00007fe665a1b993 in pread64 () from /lib/libpthread.so.0 #1 0x00000000009227bf in os_file_pread () #2 0x0000000000923156 in os_file_read_fuc () #3 0x0000000000925ee2 in os_aio_func () #4 0x00000000008eb490 in fil_io () #5 0x00000000008bef7a in buf_read_page_low () #6 0x00000000008bf488 in buf_read_page () #7 0x00000000008b4230 in buf_page_get_gen () #8 0x000000000089de3c in btr_cur_open_at_rnd_pos_func () #9 0x00000000008fe37f in ibuf_contract_ext () #10 0x00000000008fe5a0 in ibuf_contract_for_n_pages () #11 0x000000000086bb2e in srv_master_thread () #12 0x00007fe665a138ca in start_thread () from /lib/libpthread.so.0 #13 0x00007fe664573b6d in clone () from /lib/libc.so.6 #14 0x0000000000000000 in ?? ()

Thread 5 (Thread 0x7fde8802a700 (LWP 535)): 
 #0  0x00007fe665a1b993 in pread64 () from /lib/libpthread.so.0 
 #1  0x00000000009227bf in os_file_pread () 
 #2  0x0000000000923156 in os_file_read_fuc () 
 #3  0x0000000000925ee2 in os_aio_func () 
 #4  0x00000000008eb490 in fil_io () 
 #5  0x00000000008bef7a in buf_read_page_low () 
 #6  0x00000000008bf488 in buf_read_page () 
 #7  0x00000000008b4230 in buf_page_get_gen () 
 #8  0x000000000089de3c in btr_cur_open_at_rnd_pos_func () 
 #9  0x00000000008fe37f in ibuf_contract_ext () 
 #10 0x00000000008fe5a0 in ibuf_contract_for_n_pages () 
 #11 0x000000000086bb2e in srv_master_thread () 
 #12 0x00007fe665a138ca in start_thread () from /lib/libpthread.so.0 
 #13 0x00007fe664573b6d in clone () from /lib/libc.so.6 
 #14 0x0000000000000000 in ?? ()

　　问题定位并被证实了。然而为什么DBA的服务器在经历了3，4个小时后还没有完成purge操作呢?最后发现DBA测试服务器的磁盘较差，而purge需要大量的离散操作，因此导致了较长的purge与merge时间。

　　总之，innodb_fast_shutdown默认值为1，在关闭时不进行change buffer的merge操作以及purge操作。想要下次启动时，不发生这样的现象，那么必须将innodb_fast_shutdown的值设置为0。其实也就是将merge change buffer和purge的操作时间放在了关闭数据库的时候。但是，在数据库升级或者测试环境中，可能必须要进行这样的操作。