XMemcached pooled client Recv Q size is very high

Hi,

We've been using XMemcachedClient connected to twemproxy which sits behind set of memcached servers. We've kept a OpTimeout of 30 ms.

Over the time, the Recv Q(from netstat) size of the tcp socket grows really high and prompting timeouts from XMemcached. Twemproxy as a result is also getting killed by going OOM gradually

Is XMemcached client slow in receiving data? Should `TCP_RECV_BUFF_SIZE` be increased?

Few more details:
1. XMemcached version: 2.4.0
2. Protocol: Text Protocol
3. Session Idle Timeout: 60 secs
4. timeoutExceptionThreshold: 250000
5. healSessionInterval: 1 sec
6. Pool Size: 20
7. Throughput: ~ 2.2K QPS

Start at the XMemcachedClient pooled-client behavior described for version 2.4.0, using the twemproxy, text-protocol, 30 ms timeout, and 2.2K QPS conditions as the reproduction context. Inspect the TCP receive queue, timeout behavior, and TCP_RECV_BUFF_SIZE handling; done means identifying the cause of queue growth and documenting or implementing a validated fix.

Written by the indexing model from the issue text.