mongodb - Mongod 服务在执行 mongodump 后崩溃

Question

我执行了这个查询

查询：mongodump --db=elastic --collection=q_moonx_notifications_2019-08-26 --out=/home/centos/mongo-dump/

在我的 mongo db 上转储一个周围的集合

集合名称：q_moonx_notifications_2019-08-26
大小：80GB storageSize：23.6GB

这样做之后不久，mongod 服务就崩溃了。我通过 /var/log/messages 找到了问题。我知道它是由于“内存不足”问题而发生的。有人可以帮助我它是如何发生的，我怎样才能在不影响我正在运行的 mongo 服务的情况下转储单个集合。

机器有 32 GB 内存和 0 swp。

/var/log/messages 内容

Oct 11 07:07:33 ip-1.23.345.678 kernel: [<ffffffffbdb61e41>] dump_stack+0x19/0x1b Oct 11 07:07:33 ip-1.23.345.678 kernel: [<ffffffffbdb5c86a>] dump_header+0x90/0x229 Oct 11 07:07:33 ip-1.23.345.678 kernel: [<ffffffffbd700bcb>] ? cred_has_capability+0x6b/0x120 Oct 11 07:07:33 ip-1.23.345.678 kernel: [<ffffffffbd5ba4e4>] oom_kill_process+0x254/0x3d0 Oct 11 07:07:33 ip-1.23.345.678 kernel: [<ffffffffbd700c9c>] ? selinux_capable+0x1c/0x40 Oct 11 07:07:33 ip-1.23.345.678 kernel: [<ffffffffbd5bad26>] out_of_memory+0x4b6/0x4f0 Oct 11 07:07:33 ip-1.23.345.678 kernel: [<ffffffffbdb5d36e>] __alloc_pages_slowpath+0x5d6/0x724 Oct 11 07:07:33 ip-1.23.345.678 kernel: [<ffffffffbd5c1105>] __alloc_pages_nodemask+0x405/0x420 Oct 11 07:07:33 ip-1.23.345.678 kernel: [<ffffffffbd60df68>] alloc_pages_current+0x98/0x110 Oct 11 07:07:33 ip-1.23.345.678 kernel: [<ffffffffbd5b6347>] __page_cache_alloc+0x97/0xb0 Oct 11 07:07:33 ip-1.23.345.678 kernel: [<ffffffffbd5b8fa8>] filemap_fault+0x298/0x490 Oct 11 07:07:33 ip-1.23.345.678 kernel: [<ffffffffc0400d0e>] __xfs_filemap_fault+0x7e/0x1d0 [xfs] Oct 11 07:07:33 ip-1.23.345.678 kernel: [<ffffffffc0400f0c>] xfs_filemap_fault+0x2c/0x30 [xfs] Oct 11 07:07:33 ip-1.23.345.678 kernel: [<ffffffffbd5e444a>] __do_fault.isra.59+0x8a/0x100 Oct 11 07:07:33 ip-1.23.345.678 kernel: [<ffffffffbd5e49fc>] do_read_fault.isra.61+0x4c/0x1b0 Oct 11 07:07:33 ip-1.23.345.678 kernel: [<ffffffffbd5e93a4>] handle_pte_fault+0x2f4/0xd10 Oct 11 07:07:33 ip-1.23.345.678 kernel: [<ffffffffbd50cbf8>] ? get_futex_key+0x1c8/0x2c0 Oct 11 07:07:33 ip-1.23.345.678 kernel: [<ffffffffbd5ebedd>] handle_mm_fault+0x39d/0x9b0 Oct 11 07:07:33 ip-1.23.345.678 kernel: [<ffffffffbdb6f5e3>] __do_page_fault+0x203/0x500 Oct 11 07:07:33 ip-1.23.345.678 kernel: [<ffffffffbdb6f915>] do_page_fault+0x35/0x90 Oct 11 07:07:33 ip-1.23.345.678 kernel: [<ffffffffbdb6b758>] page_fault+0x28/0x30 Oct 11 07:07:33 ip-1.23.345.678 kernel: Mem-Info: Oct 11 07:07:33 ip-1.23.345.678 kernel: active_anon:7972560 inactive_anon:30565 isolated_anon:0#012 active_file:2831 inactive_file:4651 isolated_file:0#012 unevictable:0 dirty:0 writeback:5 unstable:0#012 slab_reclaimable:42065 slab_unreclaimable:12016#012 mapped:18928 shmem:55424 pagetables:19349 bounce:0#012 free:49154 free_pcp:558 free_cma:0 Oct 11 07:07:33 ip-1.23.345.678 kernel: Node 0 DMA free:15904kB min:32kB low:40kB high:48kB active_anon:0kB inactive_anon:0kB active_file:0kB inactive_file:0kB unevictable:0kB isolated(anon):0kB isolated(file):0kB present:15988kB managed:15904kB mlocked:0kB dirty:0kB writeback:0kB mapped:0kB shmem:0kB slab_reclaimable:0kB slab_unreclaimable:0kB kernel_stack:0kB pagetables:0kB unstable:0kB bounce:0kB free_pcp:0kB local_pcp:0kB free_cma:0kB writeback_tmp:0kB pages_scanned:0 all_unreclaimable? yes Oct 11 07:07:33 ip-1.23.345.678 kernel: lowmem_reserve[]: 0 3597 31992 31992 Oct 11 07:07:33 ip-1.23.345.678 kernel: Node 0 DMA32 free:121020kB min:7596kB low:9492kB high:11392kB active_anon:3397760kB inactive_anon:11020kB active_file:284kB inactive_file:508kB unevictable:0kB isolated(anon):0kB isolated(file):0kB present:3915776kB managed:3684320kB mlocked:0kB dirty:0kB writeback:0kB mapped:5892kB shmem:14892kB slab_reclaimable:131668kB slab_unreclaimable:5368kB kernel_stack:1472kB pagetables:7364kB unstable:0kB bounce:0kB free_pcp:1184kB local_pcp:0kB free_cma:0kB writeback_tmp:0kB pages_scanned:2829 all_unreclaimable? yes Oct 11 07:07:33 ip-1.23.345.678 kernel: lowmem_reserve[]: 0 0 28394 28394 Oct 11 07:07:33 ip-1.23.345.678 kernel: Node 0 Normal free:66532kB min:59952kB low:74940kB high:89928kB active_anon:28492480kB inactive_anon:111240kB active_file:11040kB inactive_file:11684kB unevictable:0kB isolated(anon):0kB isolated(file):0kB present:29622272kB managed:29079004kB mlocked:0kB dirty:0kB writeback:20kB mapped:69820kB shmem:206804kB slab_reclaimable:36592kB slab_unreclaimable:42696kB kernel_stack:6720kB pagetables:70032kB unstable:0kB bounce:0kB free_pcp:3320kB local_pcp:0kB free_cma:0kB writeback_tmp:0kB pages_scanned:8574 all_unreclaimable? no Oct 11 07:07:33 ip-1.23.345.678 kernel: lowmem_reserve[]: 0 0 0 0 Oct 11 07:07:33 ip-1.23.345.678 kernel: Node 0 DMA: 0*4kB 0*8kB 0*16kB 1*32kB (U) 2*64kB (U) 1*128kB (U) 1*256kB (U) 0*512kB 1*1024kB (U) 1*2048kB (M) 3*4096kB (M) = 15904kB Oct 11 07:07:33 ip-1.23.345.678 kernel: Node 0 DMA32: 2724*4kB (UEM) 1319*8kB (UEM) 2734*16kB (UEM) 1065*32kB (UEM) 296*64kB (UEM) 32*128kB (UEM) 0*256kB 0*512kB 0*1024kB 0*2048kB 0*4096kB = 122312kB Oct 11 07:07:33 ip-1.23.345.678 kernel: Node 0 Normal: 10268*4kB (UEM) 3615*8kB (UEM) 0*16kB 0*32kB 0*64kB 0*128kB 0*256kB 0*512kB 0*1024kB 0*2048kB 0*4096kB = 69992kB Oct 11 07:07:33 ip-1.23.345.678 kernel: Node 0 hugepages_total=0 hugepages_free=0 hugepages_surp=0 hugepages_size=1048576kB Oct 11 07:07:33 ip-1.23.345.678 kernel: Node 0 hugepages_total=0 hugepages_free=0 hugepages_surp=0 hugepages_size=2048kB Oct 11 07:07:33 ip-1.23.345.678 kernel: 61902 total pagecache pages Oct 11 07:07:33 ip-1.23.345.678 kernel: 0 pages in swap cache Oct 11 07:07:33 ip-1.23.345.678 kernel: Swap cache stats: add 0, delete 0, find 0/0 Oct 11 07:07:33 ip-1.23.345.678 kernel: Free swap = 0kB Oct 11 07:07:33 ip-1.23.345.678 kernel: Total swap = 0kB Oct 11 07:07:33 ip-1.23.345.678 kernel: 8388509 pages RAM Oct 11 07:07:33 ip-1.23.345.678 kernel: 0 pages HighMem/MovableOnly Oct 11 07:07:33 ip-1.23.345.678 kernel: 193702 pages reserved Oct 11 07:07:33 ip-1.23.345.678 kernel: [ pid ] uid tgid total_vm rss nr_ptes swapents oom_score_adj name Oct 11 07:07:33 ip-1.23.345.678 kernel: [ 2415] 0 2415 55590 32605 114 0 0 systemd-journal Oct 11 07:07:33 ip-1.23.345.678 kernel: [ 2456] 0 2456 11953 611 25 0 -1000 systemd-udevd Oct 11 07:07:33 ip-1.23.345.678 kernel: [ 2704] 0 2704 15511 170 29 0 -1000 auditd Oct 11 07:07:33 ip-1.23.345.678 kernel: [ 4346] 32 4346 18412 189 38 0 0 rpcbind Oct 11 07:07:33 ip-1.23.345.678 kernel: [ 4464] 81 4464 16600 204 34 0 -900 dbus-daemon Oct 11 07:07:33 ip-1.23.345.678 kernel: [ 4532] 998 4532 29446 143 29 0 0 chronyd Oct 11 07:07:33 ip-1.23.345.678 kernel: [ 4588] 0 4588 6652 156 19 0 0 systemd-logind Oct 11 07:07:33 ip-1.23.345.678 kernel: [ 4589] 999 4589 153057 1381 63 0 0 polkitd Oct 11 07:07:33 ip-1.23.345.678 kernel: [ 4592] 0 4592 5416 101 14 0 0 irqbalance Oct 11 07:07:33 ip-1.23.345.678 kernel: [ 4596] 0 4596 50404 162 38 0 0 gssproxy Oct 11 07:07:33 ip-1.23.345.678 kernel: [ 4940] 0 4940 26839 508 51 0 0 dhclient Oct 11 07:07:33 ip-1.23.345.678 kernel: [ 5035] 0 5035 143455 3309 99 0 0 tuned Oct 11 07:07:33 ip-1.23.345.678 kernel: [ 5102] 0 5102 31253 535 58 0 0 nginx Oct 11 07:07:33 ip-1.23.345.678 kernel: [ 5103] 995 5103 31375 641 59 0 0 nginx Oct 11 07:07:33 ip-1.23.345.678 kernel: [ 5104] 995 5104 31375 641 59 0 0 nginx Oct 11 07:07:33 ip-1.23.345.678 kernel: [ 5105] 995 5105 31375 641 59 0 0 nginx Oct 11 07:07:33 ip-1.23.345.678 kernel: [ 5106] 995 5106 31375 641 59 0 0 nginx Oct 11 07:07:33 ip-1.23.345.678 kernel: [ 5107] 995 5107 31375 641 59 0 0 nginx Oct 11 07:07:33 ip-1.23.345.678 kernel: [ 5108] 995 5108 31375 641 59 0 0 nginx Oct 11 07:07:33 ip-1.23.345.678 kernel: [ 5109] 995 5109 31375 641 59 0 0 nginx Oct 11 07:07:33 ip-1.23.345.678 kernel: [ 5110] 995 5110 31375 641 59 0 0 nginx Oct 11 07:07:33 ip-1.23.345.678 kernel: [ 5183] 0 5183 22603 310 42 0 0 master Oct 11 07:07:33 ip-1.23.345.678 kernel: [ 5189] 89 5189 22673 286 43 0 0 qmgr Oct 11 07:07:33 ip-1.23.345.678 kernel: [ 5231] 997 5231 4365796 4120011 8150 0 0 mongod Oct 11 07:07:33 ip-1.23.345.678 kernel: [ 5295] 0 5295 104225 16973 121 0 0 rsyslogd Oct 11 07:07:33 ip-1.23.345.678 kernel: [ 5297] 0 5297 28189 267 58 0 -1000 sshd Oct 11 07:07:33 ip-1.23.345.678 kernel: [ 5337] 0 5337 31580 194 18 0 0 crond Oct 11 07:07:33 ip-1.23.345.678 kernel: [ 5343] 0 5343 27523 50 10 0 0 agetty Oct 11 07:07:33 ip-1.23.345.678 kernel: [ 5347] 0 5347 27523 50 13 0 0 agetty Oct 11 07:07:33 ip-1.23.345.678 kernel: [ 5662] 27 5662 691356 97174 303 0 0 mysqld Oct 11 07:07:33 ip-1.23.345.678 kernel: [ 7361] 996 7361 12739660 2366239 5813 0 0 java Oct 11 07:07:33 ip-1.23.345.678 kernel: [ 7462] 996 7462 17192 173 30 0 0 controller Oct 11 07:07:33 ip-1.23.345.678 kernel: [ 7661] 1000 7661 3588101 1239871 2579 0 0 java Oct 11 07:07:33 ip-1.23.345.678 kernel: [14974] 0 14974 371181 6509 107 0 0 metricbeat Oct 11 07:07:33 ip-1.23.345.678 kernel: [ 6781] 994 6781 430375 60775 604 0 0 node Oct 11 07:07:33 ip-1.23.345.678 kernel: [24008] 89 24008 22629 301 47 0 0 pickup Oct 11 07:07:33 ip-1.23.345.678 kernel: [25163] 0 25163 39154 367 77 0 0 sshd Oct 11 07:07:33 ip-1.23.345.678 kernel: [25167] 1000 25167 39154 366 74 0 0 sshd Oct 11 07:07:33 ip-1.23.345.678 kernel: [25168] 1000 25168 28893 149 15 0 0 bash Oct 11 07:07:33 ip-1.23.345.678 kernel: [28554] 1000 28554 260690 34619 132 0 0 mongodump Oct 11 07:07:33 ip-1.23.345.678 kernel: Out of memory: Kill process 5231 (mongod) score 503 or sacrifice child Oct 11 07:07:33 ip-1.23.345.678 kernel: Killed process 5231 (mongod) total-vm:17463184kB, anon-rss:16480044kB, file-rss:0kB, shmem-rss:0kB Oct 11 07:07:34 ip-1.23.345.678 systemd: mongod.service: main process exited, code=killed, status=9/KILL Oct 11 07:07:34 ip-1.23.345.678 systemd: Unit mongod.service entered failed state. Oct 11 07:07:34 ip-1.23.345.678 systemd: mongod.service failed. Oct 11 07:07:39 ip-1.23.345.678 systemd-logind: New session 1220 of user centos.

标签： mongodbcentos7mongodump

Answer 1

You ran into a "problem" called the "OOM-Killer".

A quote from the part of the MongoDB documentation aptly named Production notes:

Swap

Assign swap space for your systems. Allocating swap space can avoid issues with memory contention and can prevent the OOM Killer on Linux systems from killing mongod.

For the WiredTiger storage engine, given sufficient memory pressure, WiredTiger may store data in swap space.

(emphasis by me)

What basically happened is that the memory pressure on the system became critical, and the kernel decided to kill a process to free some RAM in order to ensure the system can still run. It does so by determining the "badness" of a task via

badness_for_task = total_vm_for_task / (sqrt(cpu_time_in_seconds) *
sqrt(sqrt(cpu_time_in_minutes)))

and killing the baddest task. See https://www.kernel.org/doc/gorman/html/understand/understand016.html for details.

Gist: MongoDB presumably consumes several orders of magnitude more RAM than any other process on the server, hence it get's killed by the OOM Killer when the Kernel has no option to swap out some data and thereby ensure the basic system tasks still can run.

This behaviour can basically be prevented by allocating swap, which is why it is accordingly documented in the production notes.