4 ms·

But at least it would successfully reply to at least some of requests, right? And would still keep trying to serve the requests, right? So if sufficient numbe

But at least it would successfully reply to at least some of requests, right? And would still keep trying to serve the requests, right? So if sufficient number of supernodes is brought back online then the problems should disappear.

terryjsmith 16y ago
When this happens to our websites (when all servers go down), we need to rate limit and/or shut down traffic at the load balancer level as we bring things back online, otherwise everything just continues to get swamped and goes right back down. This would be nearly impossible in a P2P network and coordinating it between locations would be an even bigger nightmare. I imagine this is why turning on an entirely new network is a more viable option for them.
- dennisgorelik 16y ago
  Why would overloaded server go down? Shouldn't it simply stop serving incoming requests if it's overloaded?
  - barrkel 16y ago
    Is there a meaningful distinction between a server that doesn't serve requests, and a server that is down?
    - dennisgorelik 16y ago
      There is a meaningful distinction between a server that serves 1% of requests and server that is down. I assume that overloaded server still serves some requests. But my assumption could be wrong, so if you have experience with that -- please share your knowledge. Another thing that baffles me: if I introduce new supernode that is sitting on new IP address -- why would all the traffic suddenly hit that node? Shouldn't it be just gradual increase in requests while more and more Skype clients discover that new supernode?
      - terryjsmith 16y ago
        It handling 1% of connections would assume that the network was the bottleneck. You are much more likely to use up the CPU, RAM, or other resources before hitting the maximum number of available sockets. In which case things are swapping or waiting for available CPU time and each individual requests becomes seconds or tens of seconds to get handled. For all intents and purposes, that machine is dead. As to your second point, I think you are right. I assume that is what the mega-supernode is: a network of machines who's resources are as high as can be to handle all of the connections and try to beat the bottlenecks.
      - moe 16y ago
        I assume that overloaded server still serves some requests. See http://en.wikipedia.org/wiki/Thundering_herd_problem http://en.wikipedia.org/wiki/Thundering_herd_problem Many types of systems need a warm up period before they can realize their full performance. In web applications a controlled warm up is often needed to prime the caches. In P2P applications - which you can't easily "reboot" as a whole - the restoration of a steady state can be much more complex. Shouldn't it be just gradual increase in requests while more and more Skype clients discover that new supernode? In theory, yes. In practice this seems to be a case of http://en.wikipedia.org/wiki/Cascading_failure http://en.wikipedia.org/wiki/Cascading_failure The remaining supernodes either can't handle the aggregate load alone. Or they are being overwhelmed because the re-connection attempts from clients are not evenly distributed. Shouldn't it be just gradual increase in requests while more and more Skype clients discover that new supernode? In theory, yes. In practice there's probably a lot of http://en.wikipedia.org/wiki/Positive_feedback http://en.wikipedia.org/wiki/Positive_feedback and perhaps even http://en.wikipedia.org/wiki/Monster_wave http://en.wikipedia.org/wiki/Monster_wave going on in the skype network right now.
        jemfinch 16y ago
        This has absolutely nothing to do with the thundering herd problem. Why are you linking to seemingly random Wikipedia articles? The GP's question is valid: there's no reason why server software should crash when overloaded instead of simply degrading service.
  - dalore 16y ago
    Usually too many requests mean the machine runs out of memory. How it handles that is different, but it usually means the service goes down and might need a restart.

terryjsmith 16y ago

When this happens to our websites (when all servers go down), we need to rate limit and/or shut down traffic at the load balancer level as we bring things back online, otherwise everything just continues to get swamped and goes right back down. This would be nearly impossible in a P2P network and coordinating it between locations would be an even bigger nightmare. I imagine this is why turning on an entirely new network is a more viable option for them.

dennisgorelik 16y ago
Why would overloaded server go down? Shouldn't it simply stop serving incoming requests if it's overloaded?
- barrkel 16y ago
  Is there a meaningful distinction between a server that doesn't serve requests, and a server that is down?
  - dennisgorelik 16y ago
    There is a meaningful distinction between a server that serves 1% of requests and server that is down. I assume that overloaded server still serves some requests. But my assumption could be wrong, so if you have experience with that -- please share your knowledge. Another thing that baffles me: if I introduce new supernode that is sitting on new IP address -- why would all the traffic suddenly hit that node? Shouldn't it be just gradual increase in requests while more and more Skype clients discover that new supernode?
    - terryjsmith 16y ago
      It handling 1% of connections would assume that the network was the bottleneck. You are much more likely to use up the CPU, RAM, or other resources before hitting the maximum number of available sockets. In which case things are swapping or waiting for available CPU time and each individual requests becomes seconds or tens of seconds to get handled. For all intents and purposes, that machine is dead. As to your second point, I think you are right. I assume that is what the mega-supernode is: a network of machines who's resources are as high as can be to handle all of the connections and try to beat the bottlenecks.
    - moe 16y ago
      I assume that overloaded server still serves some requests. See http://en.wikipedia.org/wiki/Thundering_herd_problem http://en.wikipedia.org/wiki/Thundering_herd_problem Many types of systems need a warm up period before they can realize their full performance. In web applications a controlled warm up is often needed to prime the caches. In P2P applications - which you can't easily "reboot" as a whole - the restoration of a steady state can be much more complex. Shouldn't it be just gradual increase in requests while more and more Skype clients discover that new supernode? In theory, yes. In practice this seems to be a case of http://en.wikipedia.org/wiki/Cascading_failure http://en.wikipedia.org/wiki/Cascading_failure The remaining supernodes either can't handle the aggregate load alone. Or they are being overwhelmed because the re-connection attempts from clients are not evenly distributed. Shouldn't it be just gradual increase in requests while more and more Skype clients discover that new supernode? In theory, yes. In practice there's probably a lot of http://en.wikipedia.org/wiki/Positive_feedback http://en.wikipedia.org/wiki/Positive_feedback and perhaps even http://en.wikipedia.org/wiki/Monster_wave http://en.wikipedia.org/wiki/Monster_wave going on in the skype network right now.
      - jemfinch 16y ago
        This has absolutely nothing to do with the thundering herd problem. Why are you linking to seemingly random Wikipedia articles? The GP's question is valid: there's no reason why server software should crash when overloaded instead of simply degrading service.
- dalore 16y ago
  Usually too many requests mean the machine runs out of memory. How it handles that is different, but it usually means the service goes down and might need a restart.