Leon Rosenberg wrote:
...
We have 105 threads in this state over multiple hours.
Question: Could it be that we have connection leakage through keep-alive
connections? Is there are possibility to reduce them?
I understand that jboss have the same apache 11 connector, however all
extended configuration options are removed from the doc:
http://docs.jboss.org/jbossweb/7.0.x/config/http.html
I don't know Jboss at all, but assuming that it is Tomcat behind, and assuming that they
have not replaced the HTTP Connector by their own, then their documentation is wrong, and
you could try the following attributes :
keepAliveTimeout
The number of milliseconds this Connector will wait for another HTTP request before
closing the connection. The default value is to use the value that has been set for the
connectionTimeout attribute. Use a value of -1 to indicate no (i.e. infinite) timeout.
connectionTimeout
The number of milliseconds this Connector will wait, after accepting a connection, for the
request URI line to be presented. Use a value of -1 to indicate no (i.e. infinite)
timeout. The default value is 60000 (i.e. 60 seconds) but note that the standard
server.xml that ships with Tomcat sets this to 20000 (i.e. 20 seconds).
connectionTimeout can play a role if there are (nefarious) clients which establish a
connection to your server, but then just hang there and never send any request on that
connection. That's one known form of DOS attack.
A keepAliveTimeout of 60 seconds seems quite high to me. It means that
- the browser created a connection and asked for it to be "persistent"
- the browser sent a request on this connection
- the server allocated one thread to process that request
- the thread sent the response to that request
- now the thread, instead of being immediately released to the pool of idle threads (to
process some other request) hangs on to the connection, waiting to see if the browser has
another request to send on it. And it hangs so for keepAliveTimeout time (60 seconds here
in the default case).
- if another request comes within a short period of time, the benefit is that the
connection has not been closed, so the browser and server do not have the overhead of
establishing a new one (a few packets exchanged, a few thousand lines of code ran).
But if the browser has no more requests to send right now, you are wasting an open TCP
connection and a thread sitting there just waiting.
I can see this as useful nowadays if your application serves a lot of pages containing
many embedded <img> tags or the like, since the browser will not have to open a new
connection for each image that it wants to retrieve.
But even then, a few seconds of keepAlive would suffice.
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