HttpClient，ConnectionManager和怪异的池限制

Question

My WebApp is using an AWS S3 service as a storage for a bunch of files. When a request comes in, apropriate file is being fetched from S3 with Jets3t library, which uses ASF HttpClient under the hood. The problem is that the HttpClient connection manager uses some weird pool concept that enforces setting a limit of maximum connections per route and maximum connections in general. I'm used to pool adjusting its size to incoming demand, but it doesn't work that way in HttpClient. So when pool limit is reached, requests are on hold until connection is free. This somehow silently brings down performance of my WebApp (S3 service is faaar away from saturation).

I can't control in any way amount of requests coming to my WebApp, so any effort at coming up with a sane max connection limit is futile. Even when certain value might work ok for the current load, it will fail when some rapid change will come (eg website beeing crawled by search engine).

So here are my questions:

1. Is there any (may be third party) Connection Manager for HttpClient that doesn't enforce such limits?

2. If it doesn't exist, can I somehow make Connection Manager report the starvation of connection pool? If there is no hope at all I'd like to tune up max connection limit every time I'll see some message in logs.

In case anybody would like to suggest it, I've tried having separate instance of library (and thus HttpClient) per request thread. It works quite nicely, albeit I guess it consumes more resources. I might use that approach if all efforts at overcoming max connection limit will fail.

Answer 1

org.apache.http.impl.conn.PoolingHttpClientConnectionManager implements the org.apache.http.pool.ConnPoolControl interface, which provides these methods for getting the current connection pool statistics:

• PoolStats getTotalStats()
• PoolStats getStats(final T route)

You can construct the PoolingHttpClientConnectionManager instance passed to the org.apache.http.impl.client.HttpClientBuilder used to build the HttpClient , and therefore you can have a reference to that instance for querying the statistics any time you want.

Optionally, you could create a sublcass of PoolingHttpClientConnectionManager that logs the stats; eg, at requestConnection() time (but maybe only after every nth call).