apache bookeeper

PubSub

Features

  • 没有topic/partition概念，一个stream是由多个ledger组成的，每个ledger是有边界的
    createLedger(int ensSize, int writeQuorumSize, int ackQuorumSize)
  • ledger只有int id，没有名字
  • 每个entry(log)是有unique int64 id的
  • striped write: 交错存储
  • 各个存储节点bookie之间没有明确的主从关系
  • shared WAL
  • single writer
  • Quorum投票复制，通过存储在zk里的LastAddConfirmedId确保read consistency
  • bookie does not communicate with other bookies，由client进行并发broadcast/quorum

VS Kafka

vs kafka

createLedger时，客户端决定如何placement(org.apache.bookkeeper.client.EnsemblePlacementPolicy)，然后存放在zookeeper
例如，5个bookie，createLedger(3, 3, 2)

IO Model

io

  • 读写分离
  • Disk 1: Journal(WAL) Device
    • {timestamp}.txn
  • Disk 2: Ledger Device
    • 数据存放在多个ledger目录
    • LastLogMark表示index+data在此之前的都已经持久化到了Ledger Device，之前的WAL可以删除
    • 异步写
    • 而且是顺序写
      • 所有的active ledger共用一个entry logger
      • 读的时候利用ledger index/cache
  • [Disk 3]: Index Device
    • 默认Disk2和Disk3是在一起的
  • 在写入Memtable后，就可以向client ack了

IO被分成4种类型，分别优化

  • sync sequential write: shared WAL
  • async random write: group commit from Memtable
  • tail read: from Memtable
  • random read: from (index + os pagecache)

References

https://github.com/ivankelly/bookkeeper-tutorial
https://github.com/twitter/DistributedLog

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