Marcin Zajączkowski wrote:
(...)
Tracking down one problem I tried to get 503 error by reduction number of parallel connections to Tomcat (Apache - mod_jk - (JBoss) - Tomcat) to 10 (MaxThreads) and backlog to 1 (also tried with 10).

Regarding to documentation for backlog: "Any requests received when the queue is full will be refused". Unfortunately I wasn't able to get that effect (connection waits until served) using prepared action which waits for several seconds.

After review of source code I know that backlog isn't made internally by Tomcat, but is forwarded to listen() method in OS.

When maxThreads value is reached one more request hangs in a ThreadPool, but strange for me is that next requests pass through mod_jk which connect to and send it to Tomcat:

[debug] jk_open_socket::jk_connect.c (433): trying to connect socket 20 to 127.0.0.1:8009 [debug] jk_open_socket::jk_connect.c (459): socket 20 connected to 127.0.0.1:8009 [debug] ajp_connect_to_endpoint::jk_ajp_common.c (847): Connected socket 20 to (127.0.0.1:8009) [debug] ajp_connection_tcp_send_message::jk_ajp_common.c (893): sending to ajp13 pos=4 len=570 max=8192


I don't see any signs of those request in Tomcat log until some threads are freed (even after several minutes) and this request first waits in a ThreadPool and later is served by Tomcat.

I have DEBUG logs enabled for:
org.apache.tomcat
org.apache.coyote
org.apache.jk
org.apache.ajp
(something else could be useful?)

servel.xml:
<Connector port="8009" address="${jboss.bind.address}"
  emptySessionPath="true" enableLookups="false" redirectPort="8443"
  maxThreads="10" acceptCount="1" connectionTimeout="5000" backlog="1"
  protocol="AJP/1.3"/>


Could somebody tell me why connections are accepted at a Tomcat/Jboss side?



Is is possible to get 503 in described circumstances?

And why clients are received timeout (in spite of up 20 minutes delay)?


I use JBoss 4.0.3SP1 with Tomcat 5.5 and Apache 2.2.3 with mod_jk 1.2.20. Fedora Core 6.


Thanks for help
Marcin


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