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Write performance actually decreases as you add ZK servers, while read performance increases modestly: http://bit.ly/9JEUju^{Image Removed}zookeeper.apache.org/doc/current/zookeeperOver.html#Performance

See this page for a survey Patrick Hunt (http://twitter.com/phunt^{Image Removed}) did looking at operational latency with both standalone server and an ensemble of size 3. You'll notice that a single core machine running a standalone ZK ensemble (1 server) is still able to process 15k requests per second. This is orders of magnitude greater than what most applications require (if they are using ZooKeeper correctly - ie as a coordination service, and not as a replacement for a database, filestore, cache, etc...)

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The same behavior is exhibited when the leader crashes and a new one is elected. In the limit, if the leader is flip-flopping back and forth quickly, sessions will never expire since their timers are getting constantly reset.

Why is the myid file required?

The myid file contains an integer in human-readable ASCII text that represents a unique server id. When a ZooKeeper server starts, it reads its id from the myid file and then uses the id to find the port numbers, which it should listen to, from the configuration file. We do not recommend using the IP addresses of ZooKeeper servers to become the unique server ids as IP addresses can be moved from one server to another.