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<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>To your first question, you are
correct. Spread uses TCP/IP or Unix Domain Sockets for communications between
client libraries and the daemons, and for daemon to daemon communication it
uses UDP. Within the daemon to daemon communication for data traffic
within a shared network Segments, spread uses either multicast or broadcast.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Spread can detect process and network
faults out of the box. It is tuned currently to work on WAN and LANs and
commodity hardware. As such, it has to have its timeouts set in such a
way as not to decide that normal network latency is perceived as a fault.
Furthermore since Spread is software itself, it competes for CPU time with
other processes and the OS and can get swapped out, therefore leading to
latency delays in processing packets. Finally Spread uses a ring protocol
for control traffic and heartbeat. As such, as the number of servers
grows, the latency necessary for the token to circulate between the daemons
grows. All these reasons add more latency that Spread is tuned to be able
to handle as normal and NOT process or network faults. Therefore if you want
to be able to detect process and network faults faster, you can set the
timeouts lower, but you must also remove the cases of normal latency, so as they
not to be perceived as faults. <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Since you are running on a LAN and not a
WAN, this helps already reduce a lot of the inbuilt network latency. I
would further recommend running a real-time kernel and setting the Spread
daemon process priorities higher so as to minimize the amount of time the
Spread process is swapped out. Finally I would keep the number of Spread
daemons low enough so as the latency for each daemon to circulate a token, and
do the processing necessary when it gets the token, is minimized. Doing
all this and setting the token_timeout lower can increase your notification of
network and process faults. Some clients have gotten this down to around
the order of ~1s. However, getting is down to 10ms may not be
possible. The granularity of scheduling on commodity hardware and <st1:City
w:st="on"><st1:place w:st="on">OSs</st1:place></st1:City> is usually not fine
grain enough. So I’m not sure ANY software solution will work.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Feel free to contact me directly at Spread
Concepts.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Jacob<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
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<p class=MsoNormal><b><font size=2 face=Tahoma><span style='font-size:10.0pt;
font-family:Tahoma;font-weight:bold'>From:</span></font></b><font size=2
face=Tahoma><span style='font-size:10.0pt;font-family:Tahoma'>
spread-users-bounces@lists.spread.org
[mailto:spread-users-bounces@lists.spread.org] <b><span style='font-weight:
bold'>On Behalf Of </span></b>Shumate, James G<br>
<b><span style='font-weight:bold'>Sent:</span></b> Tuesday, October 31, 2006
8:58 AM<br>
<b><span style='font-weight:bold'>To:</span></b> spread-users@lists.spread.org<br>
<b><span style='font-weight:bold'>Subject:</span></b> [Spread-users] Spread
Architecture</span></font><o:p></o:p></p>
</div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>Spread-users,<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>I am looking for any information about how spread works
under the hood.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>Specificity does Spread use UDP between daemons and TCP
between application and daemon?<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>If it uses UDP between daemons can the timeout and number of
retries be set.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>I am currently investigation software fault tolerance for
real-time embedded systems and was wondering if SPREAD could be used in our
domain.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>Our system is on a LAN, we must process data within 10ms of
any type of fault (network cable unplugged, software crash, etc).<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>So I was wandering if SPREAD can be tuned to retry 3
times. Each retry is 2ms apart from each other. Probably have about
20 nodes on the LAN.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>Each node will be running a spread daemon and only one
application per node communicating with the daemon on that node.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>Also I noticed that older versions of SPREAD had a
multi-path capability. I assume this was for a node that had multiple
network interface cards.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>I assume it was used if one network interface card went down
SPREAD would reroute the data over the other network interface card?<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>Is there any plans to put multi-path capability into Spread
4?<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>Any information would be greatly appreciated.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>Jim<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'> <o:p></o:p></span></font></p>
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