The following error is being displayed in Plesk:
SQLSTATE[HY000]  Can't create a new thread (errno 11); if you are not out of available memory, you can consult the manual for a possible OS-dependent bug.
MySQL service is used actively, which causes it to overuse the maximum available limits for process treads.
For Ubuntu\Debian\Centos below 6:
'/etc/security/limits.conf'directly, and configure limits for MySQL as below:
mysql soft nproc 4096
For Centos 6 and above:
Create a file
'/etc/security/limits.d/91-mysql.conf' and include the same configuration as described above. The additional files is needed to override the global limit specified in the