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[Eric Desrochers <eric.desrochers@xxxxxxxxxxxxx>]

** Also affects: mysql-5.7 (Ubuntu Artful)
   Importance: Undecided
       Status: Confirmed

** Also affects: mysql-5.7 (Ubuntu Xenial)
   Importance: Undecided
       Status: New

** Also affects: mysql-5.7 (Ubuntu Zesty)
   Importance: Undecided
       Status: New

** Tags added: sts

** Changed in: mysql-5.7 (Ubuntu Artful)
     Assignee: (unassigned) => Mario Splivalo (mariosplivalo)

** Changed in: mysql-5.7 (Ubuntu Zesty)
     Assignee: (unassigned) => Mario Splivalo (mariosplivalo)

** Changed in: mysql-5.7 (Ubuntu Xenial)
     Assignee: (unassigned) => Mario Splivalo (mariosplivalo)

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https://bugs.launchpad.net/bugs/1721546

Title:
  max open files limit prevents max_connections over 214 on systemd

Status in mysql-5.7 package in Ubuntu:
  Confirmed
Status in mysql-5.7 source package in Xenial:
  New
Status in mysql-5.7 source package in Zesty:
  New
Status in mysql-5.7 source package in Artful:
  Confirmed

Bug description:
  With the default mysql-server installation on systemd versions of
  Ubuntu (xenial and above) setting max_connections to more than 214
  will not work, due to systemd imposed limits:

  root@juju-c2777d-default-1:~# grep max_connections /etc/mysql/mysql.conf.d/mysqld_settings_charm.cnf 
  max_connections = 5500

  root@juju-c2777d-default-1:~# grep max_connections /var/log/mysql/error.log 
  2017-10-05T12:41:16.958726Z 0 [Warning] Changed limits: max_connections: 214 (requested 5500)
  2017-10-05T12:41:19.198391Z 0 [Warning] Changed limits: max_connections: 214 (requested 5500)

  root@juju-c2777d-default-1:~# grep open_files /var/log/mysql/error.log 
  2017-10-05T12:41:11.824199Z 0 [Warning] Changed limits: max_open_files: 1024 (requested 5000)
  2017-10-05T12:41:16.958668Z 0 [Warning] Changed limits: max_open_files: 1024 (requested 27500)
  2017-10-05T12:41:19.198342Z 0 [Warning] Changed limits: max_open_files: 1024 (requested 27500)

  
  As can be seen, mysql tries to increase the open files limit to 27500, but due to systemd imposed limitation it fails to do so, and then it selects maximum possible number of connections, based on open files limit.

  
  This was the problem with default setups with pre-systemd installs, but upstart allowed mysqld to change the limit of open files before mysqld drops privileges from root to mysql system user.
  Even before that, on sysV init, there was a wrapper, mysqld_safe, which run as root, used ulimit to change the open files limit and then started mysqld as mysql user.

  
  Would it make sense to ship mysql-server packages with mysql.service unit files so that there is no limit for open files, or so that open files limit is substantially higher than 1024?

  This was all discussed when Ubuntu 15.10 came out, for mysql-5.6, in
  bug LP: #1434758, but I am still bringing this up for more recent
  mysql versions.

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