Database importing hangs in Plesk: Got an error reading communication packets

Symptoms

1. Database importing hangs at 100%. The database is not big.
2. MySQL server significantly loads CPU:

   PID USER      PR  NI    VIRT    RES    SHR S  %CPU %MEM    TIME+ COMMAND
   16164 mysql    20  0 2654656 748200  8044 S 201.0 18.3  2698:08 mysqld

3. Errors in
/var/log/mysql/error.log:


   275998 [Note] Aborted connection 275998 to db: 'psa' user: 'admin' host: 'localhost' (Got an error reading communication packets)

4. MySQL process list shows the following:

   show full processlist;
   | 255327 | word_user1      | localhost | word_name1              | Query  | 42625 | Waiting for table metadata lock | SELECT COUNT(*) FROM `word_name1`.`wp_wfConfig`  |
   | 255334 | word_user1      | localhost | word_name1              | Query  | 42621 | Waiting for table metadata lock | SELECT COUNT(*) FROM `word_name1`.`wp_wfConfig`  |
   | 255512 | word_user1      | localhost | word_name1              | Query  | 42288 | Waiting for table metadata lock | SELECT COUNT(*) FROM `word_name1`.`wp_wfConfig`  |

Cause

Metadata locks due to non-optimized client databases.

Resolution

Optimize the client databases and adjust MySQL instance following the instructions from article MySQL performance is slow. How to improve it? .