From: matty91@bellsouth.net
Date: Sun May 09 2004 - 17:54:36 EDT
Hello,
I have been reviewing the network tuning documentation at
http://docs.sun.com/db/doc/806-4015/6jd4gh8fj?a=view
and am trying to determine the optimal retransmission intervals
for one of our servers. This server supports direct access (ssh)
from clients dispersed throughout the world. I have noticed a high
number of retransmissions:
$ netstat -s | egrep '(tcpOutDataBytes|tcpRetransBytes)'
tcpOutDataBytes =2626324938
tcpRetransBytes =325216604
bash-2.03$ while :; do netstat -s | grep tcpRetransBytes; sleep 10; done
tcpRetransSegs =988433 tcpRetransBytes =327511820
tcpRetransSegs =988532 tcpRetransBytes =327548095
tcpRetransSegs =988588 tcpRetransBytes =327557997
tcpRetransSegs =988621 tcpRetransBytes =327566088
tcpRetransSegs =988659 tcpRetransBytes =327575023
tcpRetransSegs =988694 tcpRetransBytes =327583236
tcpRetransSegs =988748 tcpRetransBytes =327598225
tcpRetransSegs =988852 tcpRetransBytes =327621479
Based on this information, it seems that we are retransmitting roughly 2k
per second. Are there any tuning recommendations to deal with larger
propogation delays? It would seem that increasing the following may
fix the retransmission issue:
tcp_rexmit_interval_initial (read and write)
tcp_rexmit_interval_max (read and write)
tcp_rexmit_interval_min (read and write)
but I am hesitant to change anything w/o conducting a little research
first. Does anyone have any suggestions or recommendations from past
experiences? Has anyone found an optimal formula to scale the rexmit
timers to deal with remote users? On a separate note, is
there a server side equivalant to tcpAttemptFails? From reviewing some
documentation on the ORCA website, it looks like tcpAttemptFails is
incremented when outgoing connection failures occur. Is there an
easy way to coorelate these with snoop data or a "netstat -s" attribute?
I will SUMMARIZE my findings.
Thanks,
- Ryan
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