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From daniel.goul...@and.co.uk
Subject [users@httpd] Apache half-open socket behaviour
Date Tue, 21 Jul 2009 10:33:18 GMT
Hi apache-users

Platform: Solaris 10, Apache 2.2.11 compiled with Sun Studio 12, mod_jk 
1.2.28

I have been having issues while using Apache with mod_jk (although I am 
not certain that mod_jk has anything to do with this)

I have noticed that I am getting a significant number of connections in 
server-status that are getting stuck in the W (sending reply) state.

Packet captures reveal that the client side is using keep-alives, and is 
sending several requests, the last of which is followed shortly afterwards 
(~250ms) by a FIN.  This would result in a half-closed connection which as 
I understand it will stay in this state until the application closes it, 
which will result in a FIN going back to the client.

It appears that httpd has already started to send data on the socket and 
then the TCP stack takes over to repeatedly try to deliver the reply.  No 
further responses come from the client and I have a packet capture to show 
that these connections are staying in this state for longer than the 
configured TimeOut value.

On occasion we are finding that all the children will get into this state 
and the only remedy is to forcibly shut down and restart the server.

It appears that from the TCP spec the client is not obliged to send a 
reply to the repeated retransmissions, so surely Apache should obey its 
TimeOut directive here and let go of the connection?  Or should I be 
waiting for the OS to time out the half-closed connection and kill it?

Thanks

Danny

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