Mysql在ps中比在“最大MySQL内存”中使用更多的10 ps

Question

我已经在Ubuntu16.04.2上使用了MySQL 5.7.20，我注意到它目前占用的内存比我预期的要多得多。我有大约700个桌子，都是MyISAM。

我有一个128 is的RAM服务器(它使用内存来做其他事情)，MySQL内存的使用量大约是51 is。以下是ps aux | grep mysql给我的

mysql 73061051.2 63640784 54426684？Ssl Dec06 5272:34 /usr/sbin/mysqld

我希望有更多的40 be左右。启动MySQLTuner时，我得到以下信息

[--] Physical Memory : 125.8G [--] Max MySQL memory : 42.4G [--] Other process memory: 43.8G [--] Total buffers: 40.2G global + 8.8M per thread (256 max threads) [--] P_S Max memory usage: 72B [--] Galera GCache Max memory usage: 0B [OK] Maximum reached memory usage: 42.4G (33.68% of installed RAM) [OK] Maximum possible memory usage: 42.4G (33.67% of installed RAM)

这让我感到困惑，因为它说最大mysql内存是42.4GB，而当我执行ps aux时，我有几乎10 it的内存！

最后，这里是我的mysqld.conf文件

#
# 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 = 36G
max_allowed_packet = 64M
tmp_table_size = 4G
max_heap_table_size = 4G
max_connections = 256
table_open_cache = 16384
bulk_insert_buffer_size = 512M
thread_stack        = 192K
thread_cache_size       = 8
sort_buffer_size = 8M
myisam_sort_buffer_size = 8M

# 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_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/slow-query.log
#long_query_time=1
#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
[isamchk]
key_buffer_size = 36G
sort_buffer_size = 1G
read_buffer = 4M
write_buffer = 4M

你能帮我理解那些丢失10 me的东西是从哪里来的吗?我怎么才能找回它们呢？

谢谢你的帮助！

Answer 1

(这并不直接解决这个问题，而是指出了其他内存问题。)

key_buffer_size = 36G

这应该更像是20%的可用内存。key_buffer仅用于索引，OS用于缓存数据块。也就是说，不应该分配大量的RAM，这样MySQL就有了一些数据缓存。

tmp_table_size      = 4G
max_heap_table_size = 4G

这两种方法都控制复杂查询中临时表的使用。4G高得危险，因为每个连接都可以为一个SELECT分配一个甚至更多的内存块。更安全的值是可用RAM的1% (对两者都适用)。

MySQL的实际内存使用是难以捉摸的，因为有些东西(比如4G)可能会来来去去。这可能部分解决了原有问题中丢失的10 of问题。

由于许多原因，在本论坛中讨论过，您应该从MyISAM转到InnoDB。