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Tech talk   network - friend or foe
Tech talk   network - friend or foe
Tech talk   network - friend or foe
Tech talk   network - friend or foe
Tech talk   network - friend or foe
Tech talk   network - friend or foe
Tech talk   network - friend or foe
Tech talk   network - friend or foe
Tech talk   network - friend or foe
Tech talk   network - friend or foe
Tech talk   network - friend or foe
Tech talk   network - friend or foe
Tech talk   network - friend or foe
Tech talk   network - friend or foe
Tech talk   network - friend or foe
Tech talk   network - friend or foe
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Tech talk network - friend or foe

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Transcript

  • 1. Network- friend or foe
  • 2. Session outline• Good old TCP  design goals, tuning, caveats• Network congestion• LAN vs. WAN• Alternatives to TCP  TCMP – cluster transport in Coherence  SCTP• Death detection• Multicast
  • 3. TCP/IP originsMain design goal – communication infrastructure resistive to effects of thermonuclear war.• Loose network of interconnected nodes• Ad-hoc routing decisions• Very weak service guaranties
  • 4. TCP’s little dirty secretsHigh latency networks• SO_RCVBUF – caps connection bandwidthNagel’s algorithm – 200ms delay• Use TCP_ NODELAY• Does not affect localhost connectionsFirewalls• Silent connection drops
  • 5. Congestion control
  • 6. TCP summary• Thermonuclear resistance approach Cowardly in bandwidth utilization Vulnerable to random packet drops• No messages• Head of line syndrome• No multi homing
  • 7. Reality of HPC clusters• In order frame delivery• Infiniband / 10GiE – link level flow control• Low latency• No slow start needed• Congestion control cloud be drastically simplified
  • 8. UDP based transport• No flow control – much large receive buffer required to avoid losses on receiver side (e.g. sysctl -w net.core.rmem_max) – congestion prevention should be implemented
  • 9. TCMP (Oracle Coherence)• UDP based protocol• Exploit ordered delivery for fast NACK• Fast NACK -> very fast congestion detection• Extra logic to account for JVM specific behavior
  • 10. Peer death detection– essential part of any distributed algorithms
  • 11. Peer death detectionResponse timeouts are bad detector Temporary network outages  change of route, congestion, etc Temporary application outages  GC, swapping, server CPU starvation  Positive loopback effect “Corrupted witness” syndrome
  • 12. Peer death detectionIngredients of good death detection:• Process death detection using TCP• Monitor remote OS liveliness not just peer• Multiple witness suspect protocol
  • 13. SCTPSCTP – L4 protocol, TCP replacement• Works over IP or SS7• Message oriented• Multi stream delivery• Multi homing• Fast networks and jumbo frames in mind
  • 14. MulticastGroup multicast• Suitable for group communication• Not support in network hardware AFAIKHub and spoke multicast• Replicating large amounts of data• Video broadcasting• PIM/IGMP (IGMP spoofing HW support)
  • 15. IGMP multicast
  • 16. THANK YOU alexey.ragozin@gmail.com

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