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From "Asankha C. Perera" <>
Subject Expected behavior of Tomcat under load
Date Thu, 26 May 2011 09:01:23 GMT
Hi All

First of all, this is a repost from the user@ list from yesterday, as I 
think this requires a reply from a developer instead of a user.

During some performance tests, we've seen that Tomcat resets TCP 
connections under high load. To reproduce this rather consistently, a 
thread pool with a maximum of 300 threads could be configured on default 
Tomcat 6.0.32, and then 1280 ~ 2560 concurrent user requests simulated 
from a different machine over a real NW interface. I assume this could 
be reproduced with proportionately smaller numbers for both as well. The 
implementation uses a Xfire soap service.

Tomcat refusing connections, or taking longer to accept new connections, 
or taking longer to reply (causing a socket timeout) can be expected 
under such load - but what we see are TCP resets of connections to which 
a client has already sent a full HTTP request.

Is this the default behavior of Tomcat? The problem this presents is 
that the client cannot safely fail over to another instance, unlike with 
a refused connection or a connect timeout (i.e. delay in accepting)


No.     Time        Source                Destination           Protocol 
Src Port Dst Port Info
  389961 37.056567            
TCP      9062     8080     9062 > 8080 [SYN] Seq=0 Win=5792 [TCP
CHECKSUM INCORRECT] Len=0 MSS=1460 TSV=363753 TSER=363574 WS=7

  391297 37.108766            
TCP      8080     9062     8080 > 9062 [SYN, ACK] Seq=0 Ack=1 Win=5792
Len=0 MSS=1460 TSV=363383 TSER=363753 WS=7

  391298 37.108773            
TCP      9062     8080     9062 > 8080 [ACK] Seq=1 Ack=1 Win=5888 [TCP

  391893 37.115809            
HTTP     9062     8080     POST /xfire/xfire-service HTTP/1.1

  391894 37.115837            
HTTP     9062     8080     Continuation or non-HTTP traffic[Packet size
limited during capture]

  392677 37.125492            
TCP      8080     9062     8080 > 9062 [RST] Seq=1 Win=0 Len=0

Asankha C. Perera

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