I'm a bit confused on how you can measure backlog in Java. Backlog is a
TCP stack implementation setting.
Also, between TCP implementations, there is no firm definition of what
backlog actually means. does it mean SYN_RCVD or ESTABLISHED but not yet
accepted?
If I read the implementation correct, this has nothing to do with
backlog, since you are accepting the connections into the process, ie,
the handshake is done, and the accept call has returned. this connection
is no longer subject to the TCP backlog (IIRC).
This implementation, would prematurely accept connections, causing the
system to take up memory for send and receive buffers for the Java process.
Filip
Andrew Skiba wrote:
Hello,
I want to contribute a custom SocketFactory allowing to analyze the
utilization of acceptConnection attribute of a Connector. In a
properly configured production system, there should be rare situations
where connections wait for a worker thread to be handled. Our client
complained on high latency of web requests, but the measurement on
servlet did not show high latency. So we wanted to know the number of
connections which wait in socket backlog and were not accepted yet.
I solved this problem by writing a custom SocketFactory, which accepts
connections immediately and puts it in my queue until a call to
accept() will take them. So the number of waiting connections can be
monitored via JMX.
To activate this factory, the declaration of the corresponding
Connector in server.xml should be changed like in the following example.
<Connector port="8080" maxHttpHeaderSize="8192"
maxThreads="10" minSpareThreads="5" maxSpareThreads="7"
enableLookups="false" redirectPort="8443" acceptCount="10"
connectionTimeout="2000" disableUploadTimeout="true"
socketFactory="org.apache.tomcat.util.net.BacklogMeasuringServerSocketFactory"/>
No changes in existing classes are required.
Please review the code in the attachment.
Andrew Skiba.
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