1. Check max_connections Value
mysql> SHOW VARIABLES LIKE "max_connections";

+-----------------+-------+
| Variable_name   | Value |
+-----------------+-------+
| max_connections | 150   |
+-----------------+-------+
1 row in set (0.00 sec)
2. Increase max connection number
SET GLOBAL max_connections = 2000;
3. disable query_cache
set global query_cache_type=0;
set global query_cache_size=0;
flush query cache;
reset query cache;
show variables like 'query_cache_size';