HttpComponents PoolingHttpClientConnectionManager maxPerRoute and maxTotal?

Question

Can someone please explain to me what setMaxPerRoute(max) and setMaxTotal(max) do in reference to HttpComponents PoolingHttpClientConnectionManager?

Answer 1

These settings control connection pool size.

• setMaxTotal(max) defines the overal connection limit for a conneciton pool.
• setMaxPerRoute(max) defines a connection limit per one HTTP route. In simple cases you can understand this as a per target host limit. Under the hood things are a bit more interesting: HttpClient maintains a couple of HttpRoute objects, which represent a chain of hosts each, like proxy1 -> proxy2 -> targetHost. Connections are pooled on per-route basis. In simple cases, when you're using default route-building mechanism and provide no proxy suport, your routes are likely to include target host only, so per-route connection pool limit effectively becomes per-host limit.

Example:

Suppose you have setMaxPerRoute(5) and setMaxTotal(20). That means you can simultameously use up to 5 connections for every target host: 5 connections with google.com, another 5 connections with oracle.com and so on. The total amount of open connections can't however exceed 20 regardless of the number of hosts you're communicating with.