MariaDB Tuning

my.conf

[mysqld]
connect_timeout         = 15
wait_timeout            = 120
max_allowed_packet      = 16M
sort_buffer_size        = 16M
bulk_insert_buffer_size = 16M
tmp_table_size          = 32M
max_heap_table_size     = 32M
thread_handling         = pool-of-threads
#thread_pool_size        = 128
join_buffer_size = 16M
join_cache_level = 2
aria_pagecache_buffer_size = 512M
aria_sort_buffer_size           = 16M
concurrent_insert       = 2
read_buffer_size        = 2M
read_rnd_buffer_size    = 1M
low_priority_updates    = 1
key_buffer_size         = 64M
open-files-limit        = 4000
table_open_cache        = 4000
thread_cache_size       = 16K
thread_stack            = 192K

myisam_recover          = BACKUP
myisam_sort_buffer_size = 512M

query_cache_limit               = 256K
query_cache_min_res_unit        = 2k
query_cache_size                = 32M
query_cache_type                = 0

#general_log_file        = /var/log/mysql/mysql.log
#general_log             = 1
log_warnings            = 2
slow_query_log=1
slow_query_log_file     = /var/log/mysql/mariadb-slow.log
long_query_time = 10
log_slow_rate_limit     = 1000
log_slow_verbosity      = query_plan

log-queries-not-using-indexes
#log_slow_admin_statements
#log_bin                        = /var/log/mysql/mariadb-bin
#log_bin_index          = /var/log/mysql/mariadb-bin.index
expire_logs_days        = 10
max_binlog_size         = 100M

innodb_log_file_size    = 128M
innodb_buffer_pool_instances    = 12
innodb_buffer_pool_size = 12G 
innodb_log_buffer_size  = 200M
innodb_file_per_table   = 1
#innodb_open_files       = 1000
innodb_io_capacity      = 4000
innodb_read_io_threads = 64
innodb_thread_concurrency = 0
innodb_write_io_threads = 64
innodb_flush_method     = O_DIRECT
#innodb_use_atomic_writes = 1
innodb_file_format      = barracuda