Hello,
I've been trying to understand the behaviour of tomcat when handling
internal redirects. I'm testing using tomcat 9.0.38. I'm testing using
jdk8 1.8.0_265. My main test cases have been 2 forwards to the same
servlet, and then a response. Or 2 redirects to the same servlet and
then a response. Servlet as follows:
@WebServlet(loadOnStartup = 1, value = "/")
public class ConnectorLimitServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse
resp) throws IOException, ServletException {
int number = Integer.parseInt(req.getParameter("number"));
// Fake some work done at each stage of processing
try { Thread.sleep(500); } catch (InterruptedException e) {}
resp.setContentType("text/plain");
if (number <= 1) {
resp.getWriter().write("Finished " + req.getServletPath());
return;
}
switch (req.getServletPath()) {
case "/redirect":
resp.sendRedirect(new URL(req.getScheme() + "://" +
req.getServerName() + ":" + req.getServerPort() +
req.getRequestURI() + "?number=" + (number - 1)).toString());
return;
case "/forward":
final String forwardAddress = "/forward?number=" + (number - 1);
getServletContext().getRequestDispatcher(forwardAddress).forward(req,
resp);
}
}
}
It seems that under high load, 1000 threads in jmeter, Tomcat will
refuse some of the connections for nio2 connections but not for nio,
further it seems that these failures happen considerably earlier than
the configuration page would suggest would be the case. The
configuration suggests that if acceptCount is high enough for the
number of connections then they will be queued prior to reaching the
processing threads, so a small number of processing threads can exist
with a queue of connection feeding them, it seems like until
connectionTimeout is reached connections shouldn't be refused, but
that is not what occurs. In fact acceptCount seems to have very little
effect.
In short, my questions are:
Why is the nio2 connector type worse at this than nio type?
Why are connections refused before acceptCount is reached, or
connectionTimeout is reached?
I'm guessing that each forward or redirect effectively counts as an
extra connection, as removing the redirects and multipling the number
of jmeter threads suggests that is the case, am I correct here?
Also, I feel like it would help if there were better documentation
around the differences between nio2 and nio, as, for example, the
connector comparison part makes them sound almost the same.
Apologies if this has been covered elsewhere before, I have been
searching but haven't found anything particularly clear covering this.
Best regards, Peter
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