NIO.2 and GC activity

[John Franey]

Folks,

I only just became interested in nio 2, found this entry (Re: NIO.2 and GC
activity <http://markmail.org/message/kjzxpqxhtplis7hv>).

+1 for design decisions that can keep memory througput low.

I've been load testing an RTP based media server.   I have found that thread
pauses are directly correlated to media quality.  Thread pauses cause jitter
(variance in delay between packets).

When threads are active, packets can be sent at a constant rate with low
jitter.  But when threads are paused, there is a delay in one or more of the
packets.  For example, in a stream of packets at rate of once every 20ms, a
gc pause of 50ms would delay the immediate packet by 30-50ms, and the
following packet by up to 10ms.  These are tolerable, AFAICT, but could be
only a component of a larger jitter detected at the receiving end.  I've
verified the above by correlating the thread pauses (from the gc log) with
actual traffic using tcpdump/wireshark.

I think memory allocated per send/receive can eat up the heap pretty
quickly.  At 250 udp 'connections', exchanging 50 packets each way per
second, will add up to 25000 read and write requests per second.

But, perhaps jvm will allocate Futures (retun type from read and write) on
the thread stack?

Thanks,
John
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