wordpress php and mysql connection frequently disconnected

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I have a ubuntu 15.04 server with 160GB of RAM and 40 cpu cores. I am running a high traffic wordpress site with nearly 200k visitors per day. The webserver is nginx and cache server is varnish. My www.conf php configuration is 

pm = ondemand
pm.max_children = 300
pm.start_servers = 80
pm.min_spare_servers = 50
pm.max_spare_servers = 300 
pm.process_idle_timeout = 10s
pm.max_requests = 1000

The Mysql Connection configuration is

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sam-recover         = BACKUP
max_connections        = 2000
query_cache_limit   = 0
query_cache_size    = 0
log_error = /var/log/mysql/error.log
expire_logs_days    = 10
max_binlog_size   = 100M
innodb_log_file_size=268435456
innodb_log_buffer_size = 4G
innodb_buffer_pool_size = 8G
innodb_fast_shutdown = 0
innodb_flush_method = O_DIRECT
innodb_flush_log_at_trx_commit=0

[mysqldump]
quick
quote-names

[mysql]
[isamchk]
key_buffer              = 16M
sort_buffer_size = 32M

Main problem is, The php and mysql database connection disconnects frequently and it shows “Error establishing Database connection”. Mysql service is running properly. When I restart php5-fpm service, then the site starts working, but sometimes later, same thing happens.

I have tried different values for pm configurations but no any tweak actually worked.

There is nothing in the logs too. How can I debug connection problem between these two services?

Post Views: 4

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2 comments

  1. So, this is how I solved this problem. Actually the mysql connection was only 214 even though I set it 2000. I checked it using the command in mysql:

    mysql> show variables like 'max_connections';

    And the result was:

    +-----------------+-------+
| Variable_name   | Value |
+-----------------+-------+
| max_connections | 214   |
+-----------------+-------+
1 row in set (0.00 sec)

    The problem is that the maximum number of open files allowed is too small, by default 1024. So I used open files limit to increase the file open limit:

    [mysqld]
.........
open_files_limit = 8192
max_connections = 2000
.........

    … and mysqld_safe will increase the ulimit on its own before invoking the actual mysqld daemon.

    And the running MySQL server will reveal the desired max_connections setting stuck this time:

    mysql> show variables like 'max_connections';

+-----------------+-------+
| Variable_name   | Value |
+-----------------+-------+
| max_connections | 2000  |
+-----------------+-------+
1 row in set (0.00 sec)

    Hence the problem solved.

  2. Use mysqltuner to tune your mysql configuration. You are most likely running out of allocated resources and that is causing the database connection to timeout/fail.

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