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From Michi Mutsuzaki <mi...@cs.stanford.edu>
Subject Re: [Zookeeper] Zookeeper Cluster broken due to snapshot corrupted error
Date Wed, 26 Mar 2014 23:39:48 GMT
> Does snapshotting means dumping snap data on memory into disk?

Yes.

> Small snapCount would take little time for snapshotting, it means shorter
> stopping world. Do I understand properly?

The amount of time it takes to take a snapshot is proportional to the
amount of data stored in ZooKeeper. Taking snapshots more frequently
doesn't reduce the snapshot time.

ZooKeeper takes what's called 'fuzzy snapshots' and it doesn't block
writes (i.e. stop the world) during the snapshot. ZooKeeper recovers
to a consistent state by loading the fuzzy snapshot and replaying all
the transactions since the snapshot process started. This works
because all the ZooKeeper operations are idempotent.

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