I've been using MySQL 5.7.20 on Ubuntu 16.04.2 for a while and I've noticed that it currently uses far too much memory than what I would expect. I have around 700 tables which are all **MyISAM**.
I've a 128GB RAM server (which uses the memory to do other stuff) and the MySQL memory usage is around 51GB. Here is what `ps aux | grep mysql` gives me
> mysql 7306 105 41.2 63640784 54426684 ? Ssl Dec06 5272:34 /usr/sbin/mysqld
I would expect to be more around 40GB. When I start MySQLTuner, I get the following
`[--] 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)
`
This confuses me since it says that the max mysql memory is 42.4GB, whereas when I do my `ps aux` I have almost 10GB more!
Finally here is my mysqld.conf file
#
# 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
Could you help me understanding where those missing 10GB are coming from, and how can I reclaim them ?
Thanks for your help !