I get this error so frequently that the php_error log file increases 1MB every 2 seconds. and the site is very slow.
I have tried to add this line to wp-db.php
$this->query("set session wait_timeout=600" );
but it did not help.
The web server is IIS 7, latest version of mysql and wordpress
This trick will work for all WordPress versions. Open your Wordpress directory. The directory will contain the folders :
wp-admin
wp-content
wp-includes
Open wp-includes. Search for the wp-db.php file. If you found the file, open it using a text editor. Using the text editor's search tool, search for :
$this->ready = true;
Once you found the line, add the following lines just after the found line :
//WP Query Gone Away Error Fix
$this->query("set session wait_timeout=600");
You can also follow https://subinsb.com/fix-wordpress-error-mysql-server-has-gone-away link to view in more detials.
Run SHOW STATUS WHERE Variable_name LIKE '%onn%' to see how many open connections you have. Mine looks like this:
Variable_name Value
Aborted_connects 1
Connections 629
Max_used_connections 3
Ssl_client_connects 0
Ssl_connect_renegotiates 0
Ssl_finished_connects 0
Threads_connected 2
Run SHOW PROCESSLIST to see what processes are active.
The problem may be that you are opening too many connections and not closing them. Running these commands will at least give insight into what may be the issue.
<?=date("Y");?> for the year.
In my case I had a huge database (4.5 GB) imported from 5.7 to 8.0 and when running wp search-replace the error MySQL server has gone away occurred on wp-cli's queries on huge tables. So I've changed the /etc/mysql/conf.d/custom.cnf to the following:
[mysqld]
datadir = /var/lib/mysql/
socket = /var/run/mysqld/mysqld.sock
pid_file = /var/run/mysqld/mysqld.pid
tmp_table_size = 256M
max_heap_table_size = 256M
max_connections = 2000
open_files_limit = 100000
innodb_buffer_pool_instances = 8
# since 8.0 takes care of:
# innodb_buffer_pool_size
# innodb_log_file_size
# innodb_log_files_in_group
# innodb_flush_method
#https://dev.mysql.com/doc/refman/8.0/en/innodb-dedicated-server.html:
#Only consider enabling innodb_dedicated_server if the MySQL instance resides on a dedicated server where it can use all available system resources. For example, consider enabling if you run MySQL Server in a Docker container or dedicated VM that only runs MySQL. Enabling innodb_dedicated_server is not recommended if the MySQL instance shares system resources with other applications.
innodb_dedicated_server = On
innodb_buffer_pool_dump_at_shutdown = 1
innodb_buffer_pool_load_at_startup = 1
max_connections = 500
Since then not only the import of the sql file went 10 times faster (only 10 minutes by making advantage of the full machine's 50-60 GB memory), but also the wp-cli's queries now run without any issues.
Though, the key setting that helped me to get rid of the error (innodb_dedicated_server = On) is only applicable on docker containers and VPSs / dedicated servers running only MySQL. If the mysql server is running along other servers (PHP, Nginx etc) on one machine / in one container then you need to adjust the four values that innodb_dedicated_server is taking care of by yourself.
