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But I think Pulsar only stores server names and basic config info on ZK ( https://pulsar.apache.org/docs/en/administration-zk-bk/ ), which is much more managable.

Unfortunately, this is not correct. BookKeeper stores a lot of information in ZookKeeper. By extension, Pulsar (which is based on BookKeeper) also stores a lot of metadata there as well.

For example, from the BK documentation ( https://zookeeper.apache.org/doc/r3.3.6/bookkeeperOverview.h... ):

An application first creates a ledger before writing to bookies through a local BookKeeper client instance. Upon creating a ledger, a BookKeeper client writes metadata about the ledger to ZooKeeper. Each ledger currently has a single writer. This writer has to execute a close ledger operation before any other client can read from it. If the writer of a ledger does not close a ledger properly because, for example, it has crashed before having the opportunity of closing the ledger, then the next client that tries to open a ledger executes a procedure to recover it. As closing a ledger consists essentially of writing the last entry written to a ledger to ZooKeeper, the recovery procedure simply finds the last entry written correctly and writes it to ZooKeeper.



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