Mysql 錯誤提示too many connections，最近遇到這個錯誤，經過上網查資料解決了，這裡記錄下，幫助有需要的朋友，
解決方法是修改/etc/mysql/my.cnf,添加以下一行:
set-variable = max_connections=500
或在啟動命令中加上參數 max_connections=500
就是修改最大連接數,然後重啟mysql.默認的連接數是100,太少了,所以容易出現如題錯誤.
以下是mysql.com網站的相關說明:
If you get a Too many connections error when you try to connect to the mysqld server, this means that all available connections are in use by other clients.
The number of connections allowed is controlled by the max_connections system variable. Its default value is 100. If you need to support more connections, you should restart mysqld with a larger value for this variable.
mysqld actually allows max_connections+1 clients to connect. The extra connection is reserved for use by accounts that have the SUPER privilege. By granting the SUPER privilege to administrators and not to normal users (who should not need it), an administrator can connect to the server and use SHOW PROCESSLIST to diagnose problems even if the maximum number of unprivileged clients are connected. See Section 13.5.4.19, “SHOW PROCESSLIST Syntax”.
The maximum number of connections MySQL can support depends on the quality of the thread library on a given platform. Linux or Solaris should be able to support 500-1000 simultaneous connections, depending on how much RAM you have and what your clients are doing. Static Linux binaries provided by MySQL AB can support up to 4000 connections.
1.可能是mysql的max connections設置的問題
2.可能是多次insert,update操作沒有關閉session,需要在spring裡配置transaction支持。
解決:
1.修改tomcat裡的session 的time-out時間減少為20,(不是必改項)
2.對處理量大的對數據庫insert或update的操作提供transaction支持.
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下面的是解決辦法：
com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: Data source rejected establishment of connection, message from server: "Too many connections"
原因：
因為你的mysql安裝目錄下的my.ini中設定的並發連接數太少或者系統繁忙導致連接數被占滿
解決方式：
打開MYSQL安裝目錄打開MY.INI找到max_connections（在大約第93行）默認是100 一般設置到500～1000比較合適，重啟mysql,這樣1040錯誤就解決啦。
max_connections=1000
一定要重新啟動MYSQL才能生效
CMD->
net stop mysql
net start mysql
關於改變innodb_log_file_size後無法啟動mysql的問題
innodb_buffer_pool_size=768M innodb_log_file_size=256M innodb_log_buffer_size=8M innodb_additional_mem_pool_size=4M innodb_flush_log_at_trx_commit=0 innodb_thread_concurrency=20
以上是對innodb引擎的初步優化, 發現是更新innodb_log_file_size=256M時候出現了問題，只要加上這個就無法啟動,
後來才知道原來要STOP服務先，然後再刪除原來的文件………
打開/MySQL Server 5.5/data
刪除ib_logfile0, ib_logfile1........ib_logfilen
再開啟選項，成功啟動。
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