迁移到新 VPS 后，我的服务器偶尔会遇到数据库崩溃。这种情况可能在 2-3 天内发生 1-2 次。服务器在 CentOS 7 上运行 MariaDB 10.3，使用 nginx 1.16。虚拟服务器有 1 GB 内存，没有交换。在正常的日高峰流量期间，我看到大约 600 - 700 MB 的内存被占用，300 - 400 MB 可用。
我找到了以下日志/var/log/messages，从中我了解到 InnoDB 崩溃是由于内存耗尽（如果我读错了，请纠正我）。但我没有在崩溃时发现任何 DDoS 攻击或其他可疑活动。
有什么方法可以找出内存耗尽的原因吗？我应该调整一些 InnoDB 缓冲区/设置吗？我应该怎么做才能防止崩溃？
之前的 VPS 服务器采用此配置运行了 4-5 年而没有崩溃（Maria 10.1 / nginx / CentOS 6）。
我不是数据库专家，因此我非常感激任何建议。谢谢。
以下是/var/log/messages：（崩溃开始于 22:20）
May 27 22:20:01 mysite systemd: Created slice User Slice of root.
May 27 22:20:01 mysite systemd: Started Session 28800 of user root.
May 27 22:20:01 mysite systemd: Created slice User Slice of nginx.
May 27 22:20:01 mysite systemd: Started Session 28801 of user nginx.
May 27 22:20:11 mysite kernel: mysqld invoked oom-killer: gfp_mask=0x201da, order=0, oom_score_adj=0
May 27 22:20:11 mysite kernel: mysqld cpuset=/ mems_allowed=0
May 27 22:20:11 mysite kernel: CPU: 0 PID: 26756 Comm: mysqld Not tainted 3.10.0-957.12.1.el7.x86_64 #1
May 27 22:20:11 mysite kernel: Hardware name: OpenStack Foundation OpenStack Nova, BIOS 1.10.1-1ubuntu1~cloud0 04/01/2014
May 27 22:20:11 mysite kernel: Call Trace:
May 27 22:20:11 mysite kernel: [<ffffffff96363021>] dump_stack+0x19/0x1b
May 27 22:20:11 mysite kernel: [<ffffffff9635da4a>] dump_header+0x90/0x229
May 27 22:20:11 mysite kernel: [<ffffffff95d01092>] ? ktime_get_ts64+0x52/0xf0
May 27 22:20:11 mysite kernel: [<ffffffff95d582df>] ? delayacct_end+0x8f/0xb0
May 27 22:20:11 mysite kernel: [<ffffffffc033f71a>] ? virtballoon_oom_notify+0x2a/0x70 [virtio_balloon]
May 27 22:20:11 mysite kernel: [<ffffffff95dba634>] oom_kill_process+0x254/0x3d0
May 27 22:20:11 mysite kernel: [<ffffffff95dba0dd>] ? oom_unkillable_task+0xcd/0x120
May 27 22:20:11 mysite kernel: [<ffffffff95dba186>] ? find_lock_task_mm+0x56/0xc0
May 27 22:20:11 mysite kernel: [<ffffffff95dbae76>] out_of_memory+0x4b6/0x4f0
May 27 22:20:11 mysite kernel: [<ffffffff9635e54e>] __alloc_pages_slowpath+0x5d6/0x724
May 27 22:20:11 mysite kernel: [<ffffffff95dc1254>] __alloc_pages_nodemask+0x404/0x420
May 27 22:20:11 mysite kernel: [<ffffffff95e0e148>] alloc_pages_current+0x98/0x110
May 27 22:20:11 mysite kernel: [<ffffffff95db6497>] __page_cache_alloc+0x97/0xb0
May 27 22:20:11 mysite kernel: [<ffffffff95db90f8>] filemap_fault+0x298/0x490
May 27 22:20:11 mysite kernel: [<ffffffffc01fdd0e>] __xfs_filemap_fault+0x7e/0x1d0 [xfs]
May 27 22:20:11 mysite kernel: [<ffffffff95cc2e00>] ? wake_bit_function+0x40/0x40
May 27 22:20:11 mysite kernel: [<ffffffffc01fdf0c>] xfs_filemap_fault+0x2c/0x30 [xfs]
May 27 22:20:11 mysite kernel: [<ffffffff95de462a>] __do_fault.isra.59+0x8a/0x100
May 27 22:20:11 mysite kernel: [<ffffffff95de4bdc>] do_read_fault.isra.61+0x4c/0x1b0
May 27 22:20:11 mysite kernel: [<ffffffff95de9584>] handle_pte_fault+0x2f4/0xd10
May 27 22:20:11 mysite kernel: [<ffffffff95dec0bd>] handle_mm_fault+0x39d/0x9b0
May 27 22:20:11 mysite kernel: [<ffffffff963705e3>] __do_page_fault+0x203/0x4f0
May 27 22:20:11 mysite kernel: [<ffffffff963709b6>] trace_do_page_fault+0x56/0x150
May 27 22:20:11 mysite kernel: [<ffffffff9636ff42>] do_async_page_fault+0x22/0xf0
May 27 22:20:11 mysite kernel: [<ffffffff9636c788>] async_page_fault+0x28/0x30
May 27 22:20:11 mysite kernel: Mem-Info:
May 27 22:20:11 mysite kernel: active_anon:187693 inactive_anon:17396 isolated_anon:0#012 active_file:1781 inactive_file:3687 isolated_file:0#012 unevictable:0 dirty:0 writeback:0 unstable:0#012 slab_reclaimable:3639 slab_unreclaimable:7716#012 mapped:10218 shmem:27944 pagetables:13399 bounce:0#012 free:12232 free_pcp:30 free_cma:0
May 27 22:20:11 mysite kernel: Node 0 DMA free:4592kB min:708kB low:884kB high:1060kB active_anon:8412kB inactive_anon:996kB active_file:0kB inactive_file:216kB unevictable:0kB isolated(anon):0kB isolated(file):0kB present:15992kB managed:15908kB mlocked:0kB dirty:0kB writeback:0kB mapped:472kB shmem:1420kB slab_reclaimable:60kB slab_unreclaimable:380kB kernel_stack:16kB pagetables:728kB unstable:0kB bounce:0kB free_pcp:0kB local_pcp:0kB free_cma:0kB writeback_tmp:0kB pages_scanned:48 all_unreclaimable? yes
May 27 22:20:11 mysite kernel: lowmem_reserve[]: 0 972 972 972
May 27 22:20:11 mysite kernel: Node 0 DMA32 free:44212kB min:44344kB low:55428kB high:66516kB active_anon:742360kB inactive_anon:68588kB active_file:7124kB inactive_file:14532kB unevictable:0kB isolated(anon):0kB isolated(file):0kB present:1032048kB managed:998980kB mlocked:0kB dirty:0kB writeback:0kB mapped:40400kB shmem:110356kB slab_reclaimable:14496kB slab_unreclaimable:30484kB kernel_stack:2704kB pagetables:52868kB unstable:0kB bounce:0kB free_pcp:240kB local_pcp:240kB free_cma:0kB writeback_tmp:0kB pages_scanned:15611 all_unreclaimable? yes
May 27 22:20:11 mysite kernel: lowmem_reserve[]: 0 0 0 0
May 27 22:20:11 mysite kernel: Node 0 DMA: 2*4kB (EM) 3*8kB (EM) 5*16kB (UE) 4*32kB (UE) 2*64kB (UM) 1*128kB (E) 2*256kB (UE) 3*512kB (UEM) 2*1024kB (UE) 0*2048kB 0*4096kB = 4592kB
May 27 22:20:11 mysite kernel: Node 0 DMA32: 403*4kB (UEM) 597*8kB (UEM) 288*16kB (UEM) 116*32kB (UEM) 41*64kB (UEM) 30*128kB (UEM) 18*256kB (UEM) 18*512kB (UEM) 7*1024kB (UEM) 1*2048kB (U) 0*4096kB = 44212kB
May 27 22:20:11 mysite kernel: Node 0 hugepages_total=0 hugepages_free=0 hugepages_surp=0 hugepages_size=2048kB
May 27 22:20:11 mysite kernel: 33433 total pagecache pages
May 27 22:20:11 mysite kernel: 0 pages in swap cache
May 27 22:20:11 mysite kernel: Swap cache stats: add 0, delete 0, find 0/0
May 27 22:20:11 mysite kernel: Free swap = 0kB
May 27 22:20:11 mysite kernel: Total swap = 0kB
May 27 22:20:11 mysite kernel: 262010 pages RAM
May 27 22:20:11 mysite kernel: 0 pages HighMem/MovableOnly
May 27 22:20:11 mysite kernel: 8288 pages reserved
May 27 22:20:11 mysite kernel: [ pid ] uid tgid total_vm rss nr_ptes swapents oom_score_adj name
May 27 22:20:11 mysite kernel: [ 1321] 0 1321 9404 357 23 0 0 systemd-journal
May 27 22:20:11 mysite kernel: [ 1349] 0 1349 11119 141 24 0 -1000 systemd-udevd
May 27 22:20:11 mysite kernel: [ 1573] 0 1573 13880 114 28 0 -1000 auditd
May 27 22:20:11 mysite kernel: [ 1933] 81 1933 14524 138 34 0 -900 dbus-daemon
May 27 22:20:11 mysite kernel: [ 1961] 0 1961 48774 118 35 0 0 gssproxy
May 27 22:20:11 mysite kernel: [ 2001] 0 2001 6594 83 17 0 0 systemd-logind
May 27 22:20:11 mysite kernel: [ 2027] 999 2027 153158 1754 59 0 0 polkitd
May 27 22:20:11 mysite kernel: [ 2116] 998 2116 29446 115 30 0 0 chronyd
May 27 22:20:11 mysite kernel: [ 2385] 0 2385 89521 5530 94 0 0 firewalld
May 27 22:20:11 mysite kernel: [ 2961] 0 2961 26866 500 49 0 0 dhclient
May 27 22:20:11 mysite kernel: [ 3022] 0 3022 143481 2781 98 0 0 tuned
May 27 22:20:11 mysite kernel: [ 3189] 0 3189 22577 280 44 0 0 master
May 27 22:20:11 mysite kernel: [ 3191] 89 3191 22647 286 43 0 0 qmgr
May 27 22:20:11 mysite kernel: [ 3228] 0 3228 28216 255 58 0 -1000 sshd
May 27 22:20:11 mysite kernel: [ 3229] 0 3229 66328 1182 59 0 0 rsyslogd
May 27 22:20:11 mysite kernel: [ 3235] 0 3235 31579 170 18 0 0 crond
May 27 22:20:11 mysite kernel: [ 3236] 0 3236 27526 33 10 0 0 agetty
May 27 22:20:11 mysite kernel: [ 3237] 0 3237 27526 33 11 0 0 agetty
May 27 22:20:11 mysite kernel: [15958] 0 15958 130428 6710 147 0 0 php-fpm
May 27 22:20:11 mysite kernel: [15982] 0 15982 14721 288 25 0 0 nginx
May 27 22:20:11 mysite kernel: [15983] 997 15983 15403 975 31 0 0 nginx
May 27 22:20:11 mysite kernel: [21323] 997 21323 245378 11185 347 0 0 php-fpm
May 27 22:20:11 mysite kernel: [21327] 997 21327 246079 12329 348 0 0 php-fpm
May 27 22:20:11 mysite kernel: [21331] 997 21331 244508 9902 345 0 0 php-fpm
May 27 22:20:11 mysite kernel: [21582] 997 21582 225663 12179 340 0 0 php-fpm
May 27 22:20:11 mysite kernel: [ 4073] 997 4073 224018 8808 337 0 0 php-fpm
May 27 22:20:11 mysite kernel: [ 4076] 997 4076 223517 8433 335 0 0 php-fpm
May 27 22:20:11 mysite kernel: [ 5510] 997 5510 244374 7954 342 0 0 php-fpm
May 27 22:20:11 mysite kernel: [ 5517] 997 5517 244782 8575 344 0 0 php-fpm
May 27 22:20:11 mysite kernel: [ 5519] 997 5519 244994 9463 345 0 0 php-fpm
May 27 22:20:11 mysite kernel: [ 5520] 997 5520 244763 8907 344 0 0 php-fpm
May 27 22:20:11 mysite kernel: [ 5521] 997 5521 223316 8418 335 0 0 php-fpm
May 27 22:20:11 mysite kernel: [ 5522] 997 5522 244493 8212 343 0 0 php-fpm
May 27 22:20:11 mysite kernel: [ 5523] 997 5523 223509 9244 335 0 0 php-fpm
May 27 22:20:11 mysite kernel: [ 5524] 997 5524 223996 8921 336 0 0 php-fpm
May 27 22:20:11 mysite kernel: [ 5527] 997 5527 224017 8661 335 0 0 php-fpm
May 27 22:20:11 mysite kernel: [ 5536] 997 5536 244945 9254 346 0 0 php-fpm
May 27 22:20:11 mysite kernel: [ 5546] 997 5546 223528 8214 334 0 0 php-fpm
May 27 22:20:11 mysite kernel: [ 5551] 997 5551 244849 8735 343 0 0 php-fpm
May 27 22:20:11 mysite kernel: [ 5557] 997 5557 223438 8154 333 0 0 php-fpm
May 27 22:20:11 mysite kernel: [ 5558] 997 5558 244862 8565 344 0 0 php-fpm
May 27 22:20:11 mysite kernel: [ 5559] 997 5559 244877 8601 343 0 0 php-fpm
May 27 22:20:11 mysite kernel: [ 5561] 997 5561 223924 8706 338 0 0 php-fpm
May 27 22:20:11 mysite kernel: [ 5562] 997 5562 224018 8866 336 0 0 php-fpm
May 27 22:20:11 mysite kernel: [ 5563] 997 5563 224008 9187 335 0 0 php-fpm
May 27 22:20:11 mysite kernel: [ 5564] 997 5564 244965 8904 344 0 0 php-fpm
May 27 22:20:11 mysite kernel: [ 5566] 997 5566 244403 8290 348 0 0 php-fpm
May 27 22:20:11 mysite kernel: [ 5567] 997 5567 244920 9447 344 0 0 php-fpm
May 27 22:20:11 mysite kernel: [ 5568] 997 5568 244514 8736 343 0 0 php-fpm
May 27 22:20:11 mysite kernel: [ 5569] 997 5569 223477 7876 334 0 0 php-fpm
May 27 22:20:11 mysite kernel: [ 5570] 997 5570 224004 9054 335 0 0 php-fpm
May 27 22:20:11 mysite kernel: [ 5574] 997 5574 223319 7945 333 0 0 php-fpm
May 27 22:20:11 mysite kernel: [ 5575] 997 5575 244729 8709 343 0 0 php-fpm
May 27 22:20:11 mysite kernel: [ 5576] 997 5576 223435 8296 336 0 0 php-fpm
May 27 22:20:11 mysite kernel: [ 5577] 997 5577 244711 8679 343 0 0 php-fpm
May 27 22:20:11 mysite kernel: [ 5578] 997 5578 244467 8119 344 0 0 php-fpm
May 27 22:20:11 mysite kernel: [26393] 996 26393 302816 41380 170 0 0 mysqld
May 27 22:20:11 mysite kernel: [10107] 89 10107 22603 271 45 0 0 pickup
May 27 22:20:11 mysite kernel: [11273] 0 11273 45598 242 45 0 0 crond
May 27 22:20:11 mysite kernel: [11274] 0 11274 45598 242 45 0 0 crond
May 27 22:20:11 mysite kernel: [11275] 0 11275 28294 45 11 0 0 sh
May 27 22:20:11 mysite kernel: [11276] 997 11276 28294 43 11 0 0 sh
May 27 22:20:11 mysite kernel: [11277] 997 11277 96384 2413 139 0 0 php
May 27 22:20:11 mysite kernel: [11278] 0 11278 50559 1613 54 0 0 python
May 27 22:20:11 mysite kernel: Out of memory: Kill process 26393 (mysqld) score 163 or sacrifice child
May 27 22:20:11 mysite kernel: Killed process 26393 (mysqld) total-vm:1211264kB, anon-rss:165520kB, file-rss:0kB, shmem-rss:0kB
May 27 22:20:11 mysite systemd: mariadb.service: main process exited, code=killed, status=9/KILL
May 27 22:20:11 mysite systemd: Unit mariadb.service entered failed state.
May 27 22:20:11 mysite systemd: mariadb.service failed.
May 27 22:20:11 mysite systemd: Removed slice User Slice of nginx.
May 27 22:20:16 mysite systemd: mariadb.service holdoff time over, scheduling restart.
May 27 22:20:16 mysite systemd: Stopped MariaDB 10.3.14 database server.
May 27 22:20:16 mysite systemd: Starting MariaDB 10.3.14 database server...
May 27 22:20:16 mysite mysqld: 2019-05-27 22:20:16 0 [Note] /usr/sbin/mysqld (mysqld 10.3.14-MariaDB-log) starting as process 11329 ...
May 27 22:20:17 mysite systemd: Started MariaDB 10.3.14 database server.
May 27 22:20:27 mysite systemd: Removed slice User Slice of root.
May 27 22:21:02 mysite systemd: Created slice User Slice of nginx.
May 27 22:21:02 mysite systemd: Started Session 28802 of user nginx.
以下是/var/log/mysql/errors.log此次坠机事件的相关信息：
Version: '10.3.14-MariaDB-log' socket: '/var/lib/mysql/mysql.sock' port: 3306 MariaDB Server
2019-05-27 22:20:16 0 [Note] InnoDB: Using Linux native AIO
2019-05-27 22:20:16 0 [Note] InnoDB: Mutexes and rw_locks use GCC atomic builtins
2019-05-27 22:20:16 0 [Note] InnoDB: Uses event mutexes
2019-05-27 22:20:16 0 [Note] InnoDB: Compressed tables use zlib 1.2.7
2019-05-27 22:20:16 0 [Note] InnoDB: Number of pools: 1
2019-05-27 22:20:16 0 [Note] InnoDB: Using SSE2 crc32 instructions
2019-05-27 22:20:16 0 [Note] InnoDB: Initializing buffer pool, total size = 128M, instances = 1, chunk size = 128M
2019-05-27 22:20:16 0 [Note] InnoDB: Completed initialization of buffer pool
2019-05-27 22:20:16 0 [Note] InnoDB: If the mysqld execution user is authorized, page cleaner thread priority can be changed. See the man page of setpriority().
2019-05-27 22:20:16 0 [Note] InnoDB: Starting crash recovery from checkpoint LSN=699238373
2019-05-27 22:20:17 0 [Note] InnoDB: 128 out of 128 rollback segments are active.
2019-05-27 22:20:17 0 [Note] InnoDB: Removed temporary tablespace data file: "ibtmp1"
2019-05-27 22:20:17 0 [Note] InnoDB: Creating shared tablespace for temporary tables
2019-05-27 22:20:17 0 [Note] InnoDB: Setting file './ibtmp1' size to 12 MB. Physically writing the file full; Please wait ...
2019-05-27 22:20:17 0 [Note] InnoDB: File './ibtmp1' size is now 12 MB.
2019-05-27 22:20:17 0 [Note] InnoDB: Waiting for purge to start
2019-05-27 22:20:17 0 [Note] InnoDB: 10.3.14 started; log sequence number 699238382; transaction id 395866
2019-05-27 22:20:17 0 [Note] Plugin 'FEEDBACK' is disabled.
2019-05-27 22:20:17 0 [Note] InnoDB: Loading buffer pool(s) from /var/lib/mysql/ib_buffer_pool
2019-05-27 22:20:17 0 [Note] Recovering after a crash using tc.log
2019-05-27 22:20:17 0 [Note] InnoDB: Buffer pool(s) load completed at 190527 22:20:17
2019-05-27 22:20:17 0 [Note] Starting crash recovery...
2019-05-27 22:20:17 0 [Note] Crash recovery finished.
2019-05-27 22:20:17 0 [Note] Server socket created on IP: '::'.
2019-05-27 22:20:17 0 [Note] Reading of all Master_info entries succeded
2019-05-27 22:20:17 0 [Note] Added new Master_info '' to hash table
2019-05-27 22:20:17 0 [Note] /usr/sbin/mysqld: ready for connections.
Version: '10.3.14-MariaDB-log' socket: '/var/lib/mysql/mysql.sock' port: 3306 MariaDB Server
我使用默认设置，没有什么特别的etc/my.cnf.d/server.cnf：
# this is only for the mysqld standalone daemon
[mysqld]
key_buffer_size=16M
max_allowed_packet=8M
# log also slow queries:
slow_query_log = 1
long_query_time = 3
slow_query_log_file=/var/log/mysql/mysite-slow-query.log
#log_queries_not_using_indexes
log_error=/var/log/mysql/mysite-errors.log
答案1
很难分析如此小的（1GB）系统的内存需求。特别是因为整个堆栈都在单个虚拟机中。
显而易见的罪魁祸首是 PHP 线程太多。它们可能处于空闲状态。nginx有办法调整运行的线程数吗？如果有，请将其设置得更低，例如6。这可能是最好的快速修复方法。
mysqltuner 的建议更多是针对性能而非内存。因此，不要进行任何此类更改；大多数更改都会通过分配更多 RAM 而加剧问题。
另一方面，对于仅有 1GB 的 RAM，buffer_pool 的 128M 太高了，非常危险。不过，除非在错误日志中看到明确指出这一点的内容，否则不要更改它（增加或减少）。