golang-MaxIdleConns与MaxIdleConnsPerHost

在业务上使用http访问，需要初始化httpClient，其中在高并发场景下，MaxIdleConns与MaxIdleConnsPerHost的配置会影响业务的请求效率。

Client.Transports属性中包含：

• MaxIdleConns 所有host的连接池最大连接数量，默认无穷大
• MaxIdleConnsPerHost 每个host的连接池最大空闲连接数,默认2
• MaxConnsPerHost 对每个host的最大连接数量，0表示不限制

相对应的代码解释(/src/net/http/transport.go:193:198:210)

// MaxIdleConns controls the maximum number of idle (keep-alive)

// connections across all hosts. Zero means no limit.

MaxIdleConns int

// MaxIdleConnsPerHost, if non-zero, controls the maximum idle

// (keep-alive) connections to keep per-host. If zero,

// DefaultMaxIdleConnsPerHost is used.

MaxIdleConnsPerHost int

// MaxConnsPerHost optionally limits the total number of

// connections per host, including connections in the dialing,

// active, and idle states. On limit violation, dials will block.

//

// Zero means no limit.

//

// For HTTP/2, this currently only controls the number of new

// connections being created at a time, instead of the total

// number. In practice, hosts using HTTP/2 only have about one

// idle connection, though.

MaxConnsPerHost int

测试：

如果MaxConnsPerHost=1，则只有一个http client被创建.

如果MaxIdleConnsPerHost=1，则会缓存一个http client.

golang 中默认http.client

newClient := &http.Client{

Timeout: time.Minute * 1, //设置超时时间

Transport: &http.Transport{

Dial: (&net.Dialer{

Timeout: 30 * time.Second, //限制建立TCP连接的时间

KeepAlive: 30 * time.Second,

}).Dial,

TLSHandshakeTimeout: 10 * time.Second, //限制 TLS握手的时间

ResponseHeaderTimeout: 10 * time.Second, //限制读取response header的时间,默认 timeout + 5*time.Second

ExpectContinueTimeout: 1 * time.Second, //限制client在发送包含 Expect: 100-continue的header到收到继续发送body的response之间的时间等待。

MaxIdleConns: 2, //所有host的连接池最大连接数量，默认无穷大

MaxIdleConnsPerHost: 1, //每个host的连接池最大空闲连接数,默认2

MaxConnsPerHost: 1, //每个host的最大连接数量

IdleConnTimeout: 3 * time.Minute, //how long an idle connection is kept in the connection pool.

},

}