MySQL和連接相關(guān)的timeout 

 前言：

今天同事問為什么查詢mysql庫時(shí)， 在數(shù)據(jù)量比較大時(shí)，會(huì)話總斷。剛開始以為是mysql的和連接有關(guān)timeout的問題，結(jié)果是網(wǎng)絡(luò)的不穩(wěn)定的原因。 

下面總結(jié)下和連接有關(guān)的timeout 

slave-net-timeout

The number of seconds to wait for more data from the master before the slave considers the connection broken, aborts the read, and tries to reconnect. The first retry occurs immediately after the timeout. The interval between retries is controlled by the MASTER_CONNECT_RETRY option for the CHANGE MASTER TO statement, and the number of reconnection attempts is limited by the --master-retry-count option. The default is 3600 seconds (one hour).
當(dāng)slave認(rèn)為連接master的連接有問題時(shí)，就等待N秒，然后斷開連接，重新連接master

net_read_timeout ：

The number of seconds to wait for more data from a connection before aborting the read. When the server is reading from the client, net_read_timeout is the timeout value controlling when to abort
在終止讀之前，從一個(gè)連接獲得數(shù)據(jù)而等待的時(shí)間秒數(shù)；當(dāng)服務(wù)正在從客戶端讀取數(shù)據(jù)時(shí)，net_read_timeout控制何時(shí)超時(shí)。 

net_write_timeout:

The number of seconds to wait for a block to be written to a connection before aborting the write.When the server is writing to the client, net_write_timeout is the timeout value controlling when to abort。
在終止寫之前，等待多少秒把block寫到連接；當(dāng)服務(wù)正在寫數(shù)據(jù)到客戶端時(shí)，net_write_timeout控制何時(shí)超時(shí)

wait_timeout

The number of seconds the server waits for activity on a noninteractive connection before closing it.
與服務(wù)器端無交互狀態(tài)的連接，直到被服務(wù)器端強(qiáng)制關(guān)閉而等待的時(shí)間

interactive_timeout ：

The number of seconds the server waits for activity on an interactive connection before closing it.
與服務(wù)器端無交互狀態(tài)的連接，直到被服務(wù)器端強(qiáng)制關(guān)閉而等待的時(shí)間

connect_timeout

The number of seconds that the mysqld server waits for a connect packet before responding with Bad handshake. The default value is 10 seconds.

等待一個(gè)連接響應(yīng)的時(shí)間 

connect_timeout：在獲取連接階段（authenticate）起作用

interactive_timeout和wait_timeout：在連接空閑階段（sleep）起作用
net_read_timeout和net_write_timeout：則是在連接繁忙階段（query）起作用。 

獲取MySQL連接是多次握手的結(jié)果，除了用戶名和密碼的匹配校驗(yàn)外，還有IP->HOST->DNS->IP驗(yàn)證，任何一步都可能因?yàn)榫W(wǎng)絡(luò)問題導(dǎo)致線程阻塞。為了防止線程浪費(fèi)在不必要的校驗(yàn)等待上，超過connect_timeout的連接請(qǐng)求將會(huì)被拒絕。 

即使沒有網(wǎng)絡(luò)問題，也不能允許客戶端一直占用連接。對(duì)于保持sleep狀態(tài)超過了wait_timeout（或interactive_timeout，取決于client_interactive標(biāo)志）的客戶端，MySQL會(huì)主動(dòng)斷開連接。

即使連接沒有處于sleep狀態(tài)，即客戶端忙于計(jì)算或者存儲(chǔ)數(shù)據(jù)，MySQL也選擇了有條件的等待。在數(shù)據(jù)包的分發(fā)過程中，客戶端可能來不及響應(yīng)（發(fā)送、接收、或者處理數(shù)據(jù)包太慢）。為了保證連接不被浪費(fèi)在無盡的等待中，MySQL也會(huì)選擇有條件（net_read_timeout和net_write_timeout）地主動(dòng)斷開連接。 

參考：

http://dev.mysql.com/doc/refman/5.5/en/server-system-variables.html

 以上就是MySQL和連接相關(guān)的timeout 的詳細(xì)整理，如有疑問請(qǐng)留言或者到本站社區(qū)交流討論，感謝閱讀，希望能幫助到大家，謝謝大家對(duì)本站的支持！

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