Hi, I'm facing some performance issues with Tomcat. I've deployed a very simple Web service on Tomcat, and when I call an operation of this Web service, the HTTP response is fragmented into many TCP segments. This sounds normal, since the HTTP response is transmitted with the "chunked" transfer coding (the response is fragmented even though it would fit in just one TCP segment).
When the HTTP response is split, Tomcat sends just the HTTP header and the beginning of the response content to the client. It only sends the remaining parts of the content when the client sends an ACK acknowledging that the first segments where received correctly. Due the delayed ACK implementation on Linux, the client will delay the ACK for a quite long period of time. This causes a long pause in the communication, increasing significantly (up to 400%) the round trip time for Web service calls. Here are the TCP segments involved in a HTTP request to a Web service (Time was 0.0 at the beginning of the segment capture): Time (absolute) Direction Content 0.155986000 client > Tomcat HTTP request header 0.156014000 client > Tomcat HTTP request body (SOAP envelope) 0.160224000 Tomcat > client HTTP response header 0.160255000 Tomcat > client HTTP response body (part 1) 0.160265000 Tomcat > client HTTP response body (part 2) 0.160276000 Tomcat > client HTTP response body (part 3) 0.199794000 client > Tomcat TCP ACK 0.199817000 Tomcat > client HTTP response body (part 4, the last one) 0.202165000 client > Tomcat TCP ACK As the data above show, Tomcat doesn't send the last part of the response until it receives an ACK from the client. And the client delays a lot (almost 40ms) before sending the (first) ACK. One option to solve this problem would be to turn off the delayed ACK on the client. Although, as far as I'm concerned, this is not possible in Linux. I've tried setting tcpNoDelay="true" on Tomcat, but the problem still persists. Even with tcpNoDelay enabled, Tomcat still doesn't send the last part of the message before receiving the ACK. Is there any way to force Tomcat not to wait the ACK from the client to send the last part of a HTTP response? Thanks in advance, -- Ivan Neto
