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From "Asankha C. Perera" <>
Subject Re: Handling requests when under load - ACCEPT and RST vs non-ACCEPT
Date Tue, 06 Nov 2012 07:56:33 GMT
Hi Chris
> First, evidently, "acceptCount" almost does not appear in the Tomcat
> source. It's real name is "backlog" if you want to do some searching.
> It's been in there forever.
Yes, I found it too; but saw that it didn't perform what an 'end user' 
would expect from Tomcat.
> Second, all three connectors (APR, JIO, NIO) (through their
> appropriate Endpoint implementation classes) faithfully configure the
> backlog for their various sockets:
> ...
> So, barring some JVM bug, the backlog is being set as appropriately as
> possible.
Although the backlog is set, you cannot depend on it alone to make 
Tomcat behave more gracefully when under too much load. As explained in 
my previous blog post, this is not because of a defect of Tomcat - but 
the way things work in reality, causing TCP and HTTP connections to be 
established, requests to be [partially]sent and subsequently face hard 
TCP resets.
> Third is the notion of playing with OP_ACCEPT on a selector. I'm no
> NIO expert, here, but I don't understand why adding OP_ACCEPT to the
> SelectionKey would change anything, here: the socket handles the
> backlog, and the behavior of the selector shouldn't affect the OS's
> TCP backlog. Doing so would be incredibly foolish: forcing the
> application to react to all incoming connections before they went into
> the backlog queue would essentially obviate the need for the backlog
> queue in the first place.
> If you can suggest something specific, here, I'd certainly be
> interested in what your suggestion is. So far, what I'm hearing is
> that "it works with HttpComponents" but I have yet to hear what "it"
> is. Are you saying that, basically, NIO sockets simply do not have a
> backlog, and we have to fake it using some other mechanism?
Sure, I've written a pure Java example [1] that illustrates what I am 
proposing. It illustrates how you could turn off accepting new 
connections, and resume normal operations once load levels returns to 



Asankha C. Perera

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