В логах ошибок MySQL появились записи:
Перед перезагрузкой резко выросло время обработки запроса сервером170125 19:06:53 mysqld_safe Starting mysqld daemon with databases from /var/lib/mysql
170125 19:06:53 [Warning] Using unique option prefix key_buffer instead of key_buffer_size is deprecated and will be removed in a future release. Please use the full n$
170125 19:06:53 [Note] /usr/sbin/mysqld (mysqld 5.5.52-0+deb8u1) starting as process 916 ...
170125 19:06:53 [Warning] Using unique option prefix myisam-recover instead of myisam-recover-options is deprecated and will be removed in a future release. Please use$
170125 19:06:53 [Note] Plugin 'FEDERATED' is disabled.
170125 19:06:53 InnoDB: The InnoDB memory heap is disabled
170125 19:06:53 InnoDB: Mutexes and rw_locks use GCC atomic builtins
170125 19:06:53 InnoDB: Compressed tables use zlib 1.2.8
170125 19:06:53 InnoDB: Using Linux native AIO
170125 19:06:53 InnoDB: Initializing buffer pool, size = 128.0M
170125 19:06:53 InnoDB: Completed initialization of buffer pool
170125 19:06:53 InnoDB: highest supported file format is Barracuda.
InnoDB: Log scan progressed past the checkpoint lsn 16405577630
170125 19:06:53 InnoDB: Database was not shut down normally!
InnoDB: Starting crash recovery.
InnoDB: Reading tablespace information from the .ibd files...
InnoDB: Restoring possible half-written data pages from the doublewrite
InnoDB: buffer...
InnoDB: Doing recovery: scanned up to log sequence number 16405585866
170125 19:06:54 InnoDB: Starting an apply batch of log records to the database...
InnoDB: Progress in percents: 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99
InnoDB: Apply batch completed
170125 19:06:55 InnoDB: Waiting for the background threads to start
170125 19:06:56 InnoDB: 5.5.52 started; log sequence number 16405585866
170125 19:06:56 [Note] Server hostname (bind-address): '0.0.0.0'; port: 3306
170125 19:06:56 [Note] - '0.0.0.0' resolves to '0.0.0.0';
170125 19:06:56 [Note] Server socket created on IP: '0.0.0.0'.
170125 19:06:56 [Note] Event Scheduler: Loaded 0 events
170125 19:06:56 [Note] /usr/sbin/mysqld: ready for connections.
Version: '5.5.52-0+deb8u1' socket: '/var/run/mysqld/mysqld.sock' port: 3306 (Debian)
Как можно выяснить причину произошедшего?