Проблема с MYSQL на сервере

На сервере раз в 5 минут (бывает и чаще) постоянно пропадает соединение с базой данных MYSQL, что делать уже не знаю. Сервер мощный (i7+32 GB DDR3). Сайты не сказать, чтобы прям очень мощные. Все сайты открываются очень быстро, ничего не тормозит.

Вот, что показывает mysqltuner:

 >>  MySQLTuner 1.3.0 - Major Hayden <major@mhtx.net>
 >>  Bug reports, feature requests, and downloads at http://mysqltuner.com/
 >>  Run with '--help' for additional options and output filtering
[OK] Logged in using credentials from debian maintenance account.
[OK] Currently running supported MySQL version 5.5.46-0+deb8u1-log
[OK] Operating on 64-bit architecture

-------- Storage Engine Statistics -------------------------------------------
[--] Status: +ARCHIVE +BLACKHOLE +CSV -FEDERATED +InnoDB +MRG_MYISAM
[--] Data in PERFORMANCE_SCHEMA tables: 0B (Tables: 17)
[--] Data in MyISAM tables: 4G (Tables: 83)
[--] Data in InnoDB tables: 667M (Tables: 194)
[!!] Total fragmented tables: 202

-------- Security Recommendations  -------------------------------------------
[OK] All database users have passwords assigned

-------- Performance Metrics -------------------------------------------------
[--] Up for: 22s (5K q [233.727 qps], 296 conn, TX: 17M, RX: 1M)
[--] Reads / Writes: 71% / 29%
[--] Total buffers: 1.3G global + 12.2M per thread (151 max threads)
[OK] Maximum possible memory usage: 3.1G (9% of installed RAM)
[OK] Slow queries: 0% (0/5K)
[OK] Highest usage of available connections: 3% (5/151)
[OK] Key buffer size / total MyISAM indexes: 256.0M/12.7G
[OK] Key buffer hit rate: 98.7% (386K cached / 5K reads)
[OK] Query cache efficiency: 76.7% (2K cached / 3K selects)
[OK] Query cache prunes per day: 0
[OK] Sorts requiring temporary tables: 8% (14 temp sorts / 172 sorts)
[!!] Joins performed without indexes: 9
[OK] Temporary tables created on disk: 16% (108 on disk / 646 total)
[OK] Thread cache hit rate: 98% (5 created / 296 connections)
[OK] Table cache hit rate: 64% (256 open / 395 opened)
[OK] Open file limit used: 21% (224/1K)
[OK] Table locks acquired immediately: 99% (2K immediate / 2K locks)
[OK] InnoDB buffer pool / data size: 1.0G/667.1M
[OK] InnoDB log waits: 0
-------- Recommendations -----------------------------------------------------
General recommendations:
    Run OPTIMIZE TABLE to defragment tables for better performance
    MySQL started within last 24 hours - recommendations may be inaccurate
    Enable the slow query log to troubleshoot bad queries
    Adjust your join queries to always utilize indexes
Variables to adjust:
    join_buffer_size (> 1.0M, or always use indexes with joins)

Менял значение join_buffer_size до 40 мб, все равно пишет увеличить.

А вот мой my.cnf

# Example MySQL config file for large systems.
#
# This is for a large system with memory = 512M where the system runs mainly
# MySQL.
#
# MySQL programs look for option files in a set of
# locations which depend on the deployment platform.
# You can copy this option file to one of those
# locations. For information about these locations, see:
# http://dev.mysql.com/doc/mysql/en/option-files.html
#
# In this file, you can use all long options that a program supports.
# If you want to know which options a program supports, run the program
# with the "--help" option.

# The following options will be passed to all MySQL clients
[client]
#password	= your_password
port		= 3306
socket		= /var/run/mysqld/mysqld.sock

# Here follows entries for some specific programs

# The MySQL server
[mysqld]
port		= 3306
socket		= /var/run/mysqld/mysqld.sock
skip-external-locking
key_buffer_size = 256M
max_allowed_packet = 1M
table_open_cache = 256
sort_buffer_size = 2M
read_buffer_size = 1M
read_rnd_buffer_size = 8M
myisam_sort_buffer_size = 64M
join_buffer_size = 1M
thread_cache_size = 8
query_cache_size= 32M
# Try number of CPU's*2 for thread_concurrency
thread_concurrency = 8

# Don't listen on a TCP/IP port at all. This can be a security enhancement,
# if all processes that need to connect to mysqld run on the same host.
# All interaction with mysqld must be made via Unix sockets or named pipes.
# Note that using this option without enabling named pipes on Windows
# (via the "enable-named-pipe" option) will render mysqld useless!
# 
#skip-networking

# Replication Master Server (default)
# binary logging is required for replication
log-bin=mysql-bin

# binary logging format - mixed recommended
binlog_format=mixed

# required unique id between 1 and 2^32 - 1
# defaults to 1 if master-host is not set
# but will not function as a master if omitted
server-id	= 1

# Replication Slave (comment out master section to use this)
#
# To configure this host as a replication slave, you can choose between
# two methods :
#
# 1) Use the CHANGE MASTER TO command (fully described in our manual) -
#    the syntax is:
#
#    CHANGE MASTER TO MASTER_HOST=<host>, MASTER_PORT=<port>,
#    MASTER_USER=<user>, MASTER_PASSWORD=<password> ;
#
#    where you replace <host>, <user>, <password> by quoted strings and
#    <port> by the master's port number (3306 by default).
#
#    Example:
#
#    CHANGE MASTER TO MASTER_HOST='125.564.12.1', MASTER_PORT=3306,
#    MASTER_USER='joe', MASTER_PASSWORD='secret';
#
# OR
#
# 2) Set the variables below. However, in case you choose this method, then
#    start replication for the first time (even unsuccessfully, for example
#    if you mistyped the password in master-password and the slave fails to
#    connect), the slave will create a master.info file, and any later
#    change in this file to the variables' values below will be ignored and
#    overridden by the content of the master.info file, unless you shutdown
#    the slave server, delete master.info and restart the slaver server.
#    For that reason, you may want to leave the lines below untouched
#    (commented) and instead use CHANGE MASTER TO (see above)
#
# required unique id between 2 and 2^32 - 1
# (and different from the master)
# defaults to 2 if master-host is set
# but will not function as a slave if omitted
#server-id       = 2
#
# The replication master for this slave - required
#master-host     =   <hostname>
#
# The username the slave will use for authentication when connecting
# to the master - required
#master-user     =   <username>
#
# The password the slave will authenticate with when connecting to
# the master - required
#master-password =   <password>
#
# The port the master is listening on.
# optional - defaults to 3306
#master-port     =  <port>
#
# binary logging - not required for slaves, but recommended
#log-bin=mysql-bin

# Uncomment the following if you are using InnoDB tables
#innodb_data_home_dir = /var/lib/mysql
#innodb_data_file_path = ibdata1:10M:autoextend
#innodb_log_group_home_dir = /var/lib/mysql
# You can set .._buffer_pool_size up to 50 - 80 %
# of RAM but beware of setting memory usage too high
innodb_buffer_pool_size = 1024M
#innodb_additional_mem_pool_size = 20M
# Set .._log_file_size to 25 % of buffer pool size
#innodb_log_file_size = 64M
#innodb_log_buffer_size = 8M
#innodb_flush_log_at_trx_commit = 1
#innodb_lock_wait_timeout = 50

[mysqldump]
quick
max_allowed_packet = 16M

[mysql]
no-auto-rehash
# Remove the next comment character if you are not familiar with SQL
#safe-updates

[myisamchk]
key_buffer_size = 128M
sort_buffer_size = 128M
read_buffer = 2M
write_buffer = 2M

[mysqlhotcopy]
interactive-timeout

Будьте добры, помогите советом, что делать?