MySQL using 100% of CPU with 1500 active connections I'm having a problem with MySQL. I have a system that runs some cron jobs and these create lots of database connections. When it reaches about 1500 active connections the cpu usage goes to 100% but memory stays fine. My server config is:

CentOS release 6.6 (Final)
Model   Intel(R) Xeon(R) CPU E5-1660 v3 @ 3.00GHz
Cores   16
Speed   1278.984 MHz
Cache   20480 KB
Memory 130GB


file my.cnf:

[mysqld]
datadir=/var/lib/mysql
socket=/var/lib/mysql/mysql.sock
user=mysql
# Disabling symbolic-links is recommended to prevent assorted security risks
symbolic-links=0


max_connect_errors=100
open-files=64

interactive_timeout=60
wait_timeout=10

max_connections=2000

max_allowed_packet=5M
tmp_table_size=100M
max_heap_table_size=100M

#query cache desativado
query_cache_type = 0
query_cache_limit = 50M

sort_buffer_size=       1M
read_buffer_size= 128K
read_rnd_buffer_size=1M
#join_buffer_size=208M
join_buffer_size=8M
key_buffer_size=20M
myisam_sort_buffer_size=10M

thread_cache_size = 30

key_buffer=100M
open_files_limit=64
default-storage-engine=MyISAM

innodb_file_per_table=1
innodb_buffer_pool_size=35G
innodb_additional_mem_pool_size=80M

query_cache_size=50M

back_log=75
expire_logs_days        = 1
max_binlog_size         = 30M

tmpdir = /var/mysqltmpdir

long_query_time=1
log_slow_queries=/var/log/mysql_slow_queries.log

[mysqld_safe]
log-error=/var/log/mysqld.log
pid-file=/var/run/mysqld/mysqld.pid
bind-address   =  *
port = 3306
You may have encountered a Von Neumann Bottleneck. 

CPU usage is expected to increase as the number of connections increases.  As the connections increase the number of active queries should also increase.  Each query will use some CPU.  Eventually, you will have enough queries to use all available CPU. 

There are some additional factors that while use more CPU as the number of concurrently running queries increase:


Time spent waiting for resource locks.  This may involve a lock spin which will consume additional CPU. 
Context switching when the O/S switches the currently running query.  This is a side effect of the multi-processing that allows you to run more than one query at a time.


Running a program like sar may provide more details on where the CPU is being used.