etcd3 vs zookeeper

一致性

etcd v3独有的特性

  • get and watch by prefix, by interval
  • lease based TTL for key sets
  • runtime reconfiguration
  • point in time backup
  • extensive metrics
  • 获取历史版本数据(这个非常有用)
    multi-version

  • mini transation DSL

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    Tx.If(
        Compare(Value("foo"), ">", "bar"),
        Compare(Value(Version("foo"), "=", 2),
        ...
    ).Then(
        Put("ok", "true")...
    ).Else(
        Put("ok", "false")...
    ).Commit()

  • leases

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    l = CreateLeases(15*second)
    Put(foo, bar, l)
    l.KeepAlive()
    l.Revoke()

  • watcher功能丰富

    • streaming watch
    • 支持index参数，不会lose event
    • recursive
  • off-heap
    内存中只保留index，大部分数据通过mmap映射到boltdb file
  • incremental snapshot

zk独有的特性

  • ephemeral znode
  • non-blocking full fuzzy snapshot
    Too busy to snap, skipping
  • key支持在N Millions
  • on-heap

etcd2

  • etcd2的key支持在10K量级，etcd3支持1M量级
    • 原因在于snapshot成本，可能导致0 qps，甚至reelection

comparison

memory footprint

2M 256B keys

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etcd2 10GB
zk    2.4GB
etcd3 0.8GB

References

https://coreos.com/blog/performance-of-etcd.html

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