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 !