MySQL“無法為緩衝池分配記憶體”記憶體使用率為 73%？

我在 DigitalOcean 液滴（1GB RAM）上託管一個 WordPress 網站。該網站的MySQL數據庫偶爾會崩潰，導致網站顯示“建立數據庫連接時出錯”。記憶體使用量在凌晨 2:40 左右下降，表明這是數據庫崩潰的時候。我查看了當天的 MySQL 日誌文件，最早的條目是上午 10 點 47 分。這是日誌文件的開頭：

2021-12-06T10:47:14.800977Z 0 [Warning] TIMESTAMP with implicit DEFAULT value is deprecated. Please use --explicit_defaults_for_timest$
2021-12-06T10:47:14.806192Z 0 [Note] /usr/sbin/mysqld (mysqld 5.7.36-0ubuntu0.18.04.1) starting as process 2810 ...
2021-12-06T10:47:14.819674Z 0 [Note] InnoDB: PUNCH HOLE support available
2021-12-06T10:47:14.819711Z 0 [Note] InnoDB: Mutexes and rw_locks use GCC atomic builtins
2021-12-06T10:47:14.819716Z 0 [Note] InnoDB: Uses event mutexes
2021-12-06T10:47:14.819720Z 0 [Note] InnoDB: GCC builtin __atomic_thread_fence() is used for memory barrier
2021-12-06T10:47:14.819723Z 0 [Note] InnoDB: Compressed tables use zlib 1.2.11
2021-12-06T10:47:14.819727Z 0 [Note] InnoDB: Using Linux native AIO
2021-12-06T10:47:14.820551Z 0 [Note] InnoDB: Number of pools: 1
2021-12-06T10:47:14.823342Z 0 [Note] InnoDB: Using CPU crc32 instructions
2021-12-06T10:47:14.825847Z 0 [Note] InnoDB: Initializing buffer pool, total size = 128M, instances = 1, chunk size = 128M
2021-12-06T10:47:14.826246Z 0 [ERROR] InnoDB: mmap(137428992 bytes) failed; errno 12
2021-12-06T10:47:14.826258Z 0 [ERROR] InnoDB: Cannot allocate memory for the buffer pool
2021-12-06T10:47:14.826262Z 0 [ERROR] InnoDB: Plugin initialization aborted with error Generic error
2021-12-06T10:47:14.826270Z 0 [ERROR] Plugin 'InnoDB' init function returned error.
2021-12-06T10:47:14.826274Z 0 [ERROR] Plugin 'InnoDB' registration as a STORAGE ENGINE failed.
2021-12-06T10:47:14.826278Z 0 [ERROR] Failed to initialize builtin plugins.
2021-12-06T10:47:14.826282Z 0 [ERROR] Aborting

2021-12-06T10:47:14.832237Z 0 [Note] Binlog end
2021-12-06T10:47:14.832297Z 0 [Note] Shutting down plugin 'CSV'
2021-12-06T10:47:14.832572Z 0 [Note] /usr/sbin/mysqld: Shutdown complete

根據日誌文件，MySQL 似乎記憶體不足。但是，Droplet 的記憶體使用率穩定在 73% 左右，直到凌晨 2:40 左右數據庫崩潰，才下降到 32%。它似乎有足夠的可用記憶體，那麼為什麼會崩潰？

編輯根據要求，這是我的 MySQL 配置文件的內容：

/etc/mysql/conf.d/mysql.cnf

[mysql]

/etc/mysql/conf.d/mysqldump.cnf

[mysqldump]
quick
quote-names
max_allowed_packet      = 16M

/etc/mysql/mysql.conf.d/mysqld.cnf

#
# The MySQL database server configuration file.
#
# You can copy this to one of:
# - "/etc/mysql/my.cnf" to set global options,
# - "~/.my.cnf" to set user-specific options.
#
# One can use all long options that the program supports.
# Run program with --help to get a list of available options and with
# --print-defaults to see which it would actually understand and use.
#
# For explanations see
# http://dev.mysql.com/doc/mysql/en/server-system-variables.html

# This will be passed to all mysql clients
# It has been reported that passwords should be enclosed with ticks/quotes
# escpecially if they contain "#" chars...
# Remember to edit /etc/mysql/debian.cnf when changing the socket location.

# Here is entries for some specific programs
# The following values assume you have at least 32M ram

[mysqld_safe]
socket          = /var/run/mysqld/mysqld.sock
nice            = 0

[mysqld]
#
# * Basic Settings
#
user            = mysql
pid-file        = /var/run/mysqld/mysqld.pid
socket          = /var/run/mysqld/mysqld.sock
port            = 3306
basedir         = /usr
datadir         = /var/lib/mysql
tmpdir          = /tmp
lc-messages-dir = /usr/share/mysql
skip-external-locking
#
# Instead of skip-networking the default is now to listen only on
# localhost which is more compatible and is not less secure.
bind-address            = 127.0.0.1
#
# * Fine Tuning
#
key_buffer_size         = 16M
max_allowed_packet      = 16M
thread_stack            = 192K
thread_cache_size       = 8
# This replaces the startup script and checks MyISAM tables if needed
# the first time they are touched
myisam-recover-options  = BACKUP
#max_connections        = 100
#table_open_cache       = 64
#thread_concurrency     = 10
#
# * Query Cache Configuration
#
query_cache_limit       = 1M
query_cache_size        = 16M
#
# * Logging and Replication
#
# Both location gets rotated by the cronjob.
# Be aware that this log type is a performance killer.
# As of 5.1 you can enable the log at runtime!
#general_log_file        = /var/log/mysql/mysql.log
#general_log             = 1
#
# Error log - should be very few entries.
#
log_error = /var/log/mysql/error.log
#
# Here you can see queries with especially long duration
#slow_query_log         = 1
#slow_query_log_file    = /var/log/mysql/mysql-slow.log
#long_query_time = 2
#log-queries-not-using-indexes
#
# The following can be used as easy to replay backup logs or for replication.
# note: if you are setting up a replication slave, see README.Debian about
#       other settings you may need to change.
#server-id              = 1
#log_bin                        = /var/log/mysql/mysql-bin.log
expire_logs_days        = 10
max_binlog_size   = 100M
#binlog_do_db           = include_database_name
#binlog_ignore_db       = include_database_name
#
# * InnoDB
#
# InnoDB is enabled by default with a 10MB datafile in /var/lib/mysql/.
# Read the manual for more InnoDB related options. There are many!
#
# * Security Features
#
# Read the manual, too, if you want chroot!
# chroot = /var/lib/mysql/
#
# For generating SSL certificates I recommend the OpenSSL GUI "tinyca".
#
# ssl-ca=/etc/mysql/cacert.pem
# ssl-cert=/etc/mysql/server-cert.pem
# ssl-key=/etc/mysql/server-key.pem

/etc/mysql/mysql.conf.d/mysqld_safe_syslog.cnf

[mysqld_safe]
syslog

在聊天中查看核心日誌後，MySQL崩潰的原因是記憶體不足。

Dec 6 02:47:13  kernel: [341799.228400] Out of memory: Kill process 23566 (mysqld) score 197 or sacrifice child
Dec 6 02:47:13  kernel: [341799.229866] Killed process 23566 (mysqld) total-vm:1168576kB, anon-rss:198536kB, file-rss:0kB, shmem-rss:0kB

在那段時間裡，有很多 Apache2 程序處於活動狀態。這意味著增加流量會導致記憶體消耗增加。結果，核心決定殺死 MySQL 以釋放記憶體。

可以執行mysqltuner分析 MySQL 配置。它提供了一些建議，有助於減少 MySQL 記憶體消耗。

然而，增加流量仍然會導致同樣的問題。因此，更可持續的解決方案是增加可用於液滴的記憶體。

引用自：https://serverfault.com/questions/1086072