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Numbers everyone should know

"Numbers everyone should know", courtesy of Jeff Dean:
* L1 cache reference                              0.5 ns
* Branch mispredict                               5 ns
* L2 cache reference                              7 ns
* Mutex lock/unlock                             100 ns
* Main memory reference                         100 ns
* Compress 1K bytes with Zippy               10,000 ns
* Send 2K bytes over 1 Gbps network          20,000 ns
* Read 1 MB sequentially from memory        250,000 ns
* Round trip within same datacenter         500,000 ns
* Disk seek                              10,000,000 ns
* Read 1 MB sequentially from network    10,000,000 ns
* Read 1 MB sequentially from disk       30,000,000 ns
* Send packet CA->Netherlands->CA       150,000,000 ns
Similarly (and courtesy of Jeff Dean and Sean Quinlan), "The Joys of Real Hardware" lists the typical problems a new cluster will experience in its first year:
  • ~0.5 overheating (power down most machines in <5 mins, ~1-2 days to recover)
  • ~1 PDU failure (~500-1000 machines suddenly disappear, ~6 hours to come back)
  • ~1 rack-move (plenty of warning, ~500-1000 machines powered down, ~6 hours)
  • ~1 network rewiring (rolling ~5% of machines down over 2-day span)
  • ~20 rack failures (40-80 machines instantly disappear, 1-6 hours to get back)
  • ~5 racks go wonky (40-80 machines see 50% packet loss)
  • ~8 network maintenances (4 might cause ~30-minute random connectivity losses)
  • ~12 router reloads (takes out DNS and external vips for a couple minutes)
  • ~3 router failures (have to immediately pull traffic for an hour)
  • ~dozens of minor 30-second blips for dns
  • ~1000 individual machine failures
  • ~thousands of hard drive failures
in addition to "slow disks, bad memory, misconfigured machines, flaky machines, etc.".

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