mysql 访问量过大，造成链接不上的情况
硬件：16核心CPU ，32G内存，100M带宽
软件，php5.6,+mysql 5.7
用途，接口调用
mysql 基本配置：
[client]
#password = your_password
port = 3306
socket = /tmp/mysql.sock
[mysqld]
binlog_cache_size = 192K
thread_stack = 384K
join_buffer_size = 4096K
query_cache_type = 0
max_heap_table_size = 1024M
port = 3306
socket = /tmp/mysql.sock
datadir = /www/server/data
skip-external-locking
performance_schema_max_table_instances=400
table_definition_cache=400
key_buffer_size = 512M
max_allowed_packet = 100G
table_open_cache = 1024
sort_buffer_size = 2048K
net_buffer_length = 8K
read_buffer_size = 2048K
read_rnd_buffer_size = 1024K
myisam_sort_buffer_size = 64M
thread_cache_size = 192
query_cache_size = 0M
tmp_table_size = 1024M
explicit_defaults_for_timestamp = true
#skip-networking
skip-name-resolve
skip-grant-tables
max_connections = 2800
max_connect_errors = 100
open_files_limit = 65535
sql-mode=NO_ENGINE_SUBSTITUTION,STRICT_TRANS_TABLES
#log-bin=mysql-bin
#binlog_format=mixed
server-id = 1
expire_logs_days = 10
slow_query_log=1
slow-query-log-file=/www/server/data/mysql-slow.log
long_query_time=3
back_log = 900
#log_queries_not_using_indexes=on
#loose-innodb-trx=0
#loose-innodb-locks=0
#loose-innodb-lock-waits=0
#loose-innodb-cmp=0
#loose-innodb-cmp-per-index=0
#loose-innodb-cmp-per-index-reset=0
#loose-innodb-cmp-reset=0
#loose-innodb-cmpmem=0
#loose-innodb-cmpmem-reset=0
#loose-innodb-buffer-page=0
#loose-innodb-buffer-page-lru=0
#loose-innodb-buffer-pool-stats=0
#loose-innodb-metrics=0
#loose-innodb-ft-default-stopword=0
#loose-innodb-ft-inserted=0
#loose-innodb-ft-deleted=0
#loose-innodb-ft-being-deleted=0
#loose-innodb-ft-config=0
#loose-innodb-ft-index-cache=0
#loose-innodb-ft-index-table=0
#loose-innodb-sys-tables=0
#loose-innodb-sys-tablestats=0
#loose-innodb-sys-indexes=0
#loose-innodb-sys-columns=0
#loose-innodb-sys-fields=0
#loose-innodb-sys-foreign=0
#loose-innodb-sys-foreign-cols=0
default_storage_engine = InnoDB
innodb_data_home_dir = /www/server/data
innodb_data_file_path = ibdata1:10M:autoextend
innodb_log_group_home_dir = /www/server/data
innodb_buffer_pool_size = 1024M
innodb_log_file_size = 512M
innodb_log_buffer_size = 128M
innodb_flush_log_at_trx_commit = 1
innodb_lock_wait_timeout = 100
innodb_max_dirty_pages_pct = 90
innodb_read_io_threads = 16
innodb_write_io_threads = 16
[mysqldump]
quick
max_allowed_packet = 16M
[mysql]
no-auto-rehash
[myisamchk]
key_buffer_size = 256M
sort_buffer_size = 4M
read_buffer = 2M
write_buffer = 2M
[mysqlhotcopy]
interactive-timeout
一旦并发量有点大，可能会有一个查询阻塞，就会造成链接不上数据库或者php报错：
connect() to unix:/tmp/php-cgi-56.sock failed (11: Resource temporarily unavailable) while connecting to upstream, client:
，问题应该在于数据库这边，数据库是独立的服务器，web有web的服务器，访问走的内网，不占用带宽。
https://blog.csdn.net/jiedushi/article/details/6015262
MySQL高效处理大量并发的数据库连接方法
检查当时的数据库联接数量，是否已经达到你参数里设置的2800，如果已经达到，那么说明连接已经满了，想办法增加最大连接数量。
观察当时cpu 内存的使用量，看看是否因为cpu繁忙导致处理延时而连接不上。
日志里应该有一些信息可供参考。
数据库的硬件配置挺好的，应该是企业生产环境下数据库配置。我谈一下我的思路首先上层应用应该是做了负载均衡会消耗很多连接还有其他的离线计算、定时任务等，所以我建议：
1、首先检查一下连接该数据库应用实例有哪些？每一个实例连接数有多少？这个很关键，一般来说公司规模变大，应用负载均衡添加，再加上离线计算统计分析，这些都会消耗数据库连接数，所以建议先排查一下应用。
2、如果应用连接数配置都正常，建议查找数据库的慢SQL，如果sql质量都很好，哪怕连接数很多也没什么大问题。
3、针对innodb的配置我感觉有些问题，建议去https://tools.percona.com/dashboard生成mysql配置，这样会好很多
我贴一个8C16G机器的配置：
# Generated by Percona Configuration Wizard (http://tools.percona.com/) version REL5-20120208
# Configuration name server-28 generated for 1479338858@qq.com at 2017-08-25 12:21:13
[mysql]
# CLIENT #
port = 3306
socket = /abc/mysql.sock
[mysqld]
# GENERAL #
user = mysql
default-storage-engine = InnoDB
socket = /abc/mysql.sock
pid-file = /abc/mysql.pid
# MyISAM #
key-buffer-size = 32M
myisam-recover = FORCE,BACKUP
# SAFETY #
max-allowed-packet = 16M
max-connect-errors = 1000000
# DATA STORAGE #
datadir = /abc/
# BINARY LOGGING #
log-bin = /abc/mysql-bin
expire-logs-days = 14
sync-binlog = 1
# REPLICATION #
relay-log = /abc/relay-bin
slave-net-timeout = 60
# CACHES AND LIMITS #
tmp-table-size = 32M
max-heap-table-size = 32M
query-cache-type = 0
query-cache-size = 0
max-connections = 500
thread-cache-size = 50
open-files-limit = 65535
table-definition-cache = 4096
table-open-cache = 4096
# INNODB #
innodb-flush-method = O_DIRECT
innodb-log-files-in-group = 2
innodb-log-file-size = 256M
innodb-flush-log-at-trx-commit = 1
innodb-file-per-table = 1
innodb-buffer-pool-size = 12G
# LOGGING #
log-error = /abc/mysql-error.log
log-queries-not-using-indexes = 1
slow-query-log = 1
slow-query-log-file = /abc/mysql-slow.log
设置下最大连接用户 希望帮你解决
经过一轮测试：高并发的情况下，会造成数据库连接不上，